THE SLOW COMRITSTION OF ETHANE. 693

LXXIL-The Slow Combustion of Ethane.

Ey WILLIAM ARTHUR BONE and WILLIAM ERNEST STOCKINGS.

TIrE present paper contains some further results of the investigation of t h e slow combustion of hydrocarbons, at temperatures below their ignition points, initiated by one of us in conjunction with Mr. Wheeler (Trans., 1902, 81, 536 ; 1903, 83, 1074). The experimental part comprises three sections dealing respectively with : (1) the interaction of ethane and oxygen at 250-400°, under pressures of 1.75 to 2.33 atmospheres, in borosilicate glass bulbs ; (2) the oxidation of ethane at 400-500°, under reduced pressure, in our ‘‘ circulation apparatus ” ; and (3) the slow combustion of ethyl alcohol and acetaidehyde.

As will be readily understood, the case of ethane has proved more complex than that of methane; this is partly due to the greater

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694 BONE AND STOCKTKGS:

number of stages involved in the combustion of ethane, and partly also to the disturbing influences of secondary processes which were entirely absent in the methane experiments. The precise signilicance of the various phenomena under discussion, in relation to the general question of the combustion of hydrocarbons, can perhaps only ho correctly gauged after a careful perusal of the evidence contained in our account of the actual experiments, but i t may assist the reader if we now summarise our main conclusions.

( 1) Under similar conditions, ethane bums much more raylidly t hnn methane, and in barosilicate glass bulbs both hydrocarbons are oxidised at temperatures much below the limiting temperature (about 400') a t which, under similar conditions, steam is appreciably formed from electrolytic gas.

(2) When ethane reacts with a quantity of oxygen insufficient to burn the whole of i t to carbon monoxide and steam, there is no prefer- ential combustion either of hydrogen or of carbon. I n the absence of the disturbing effects of secondary processes, the interaction is always marked by a diminution in the pressure of the cold products, without any deposition of carbon or liberation of hydrogen.

(3) On the other hand, the combustion proceeds in several well- defined stages, during which the oxygen enters into, and is incorporated with the hydrocarbon molecule forming oxygenated intermedia+ o products. (4) The first stage we have been able to distinguish in the process

involves the rapid formation of acetaldehyde and steam. It may perhaps be best represented as a process of hydroxylation, followed by the immediate decomposition of the unstable hydroxylnted product, thus :

H f O H i

H i There is no direct evidence of the primary formation of any ethyl

alcohol in our experiments such as would be required by the genoral theory of combustion recently advanced by Professor Armstrong (Trans., 1903, 83, 1088). But as we find that ethyl alcohol is, under similar conditions, oxidised far more rapidly than ethane itself, me cannot attach any significance to its non-occurrence among the oxidation products of ethane.* I n this connection we would romnrk

* Since the above was written, however, one of us, in oonjmiction with Dr. Julien Drtign~a~i, has detected ethyl alcoliol among the products of t hc iiitcrnc t ion of ethane an(l ozoiic a t 100" (Proc., 1904, 20, 127). It is thcrcrore highly p o b n h l e th:rt e thyl alcohol is really the prinisry oxidation product.

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THE SLOW COMBUSTION OF ETHANE. 695

that, whilst the proportions of ethane and oxygen most favourable to chemical change appear to be 1 : 1, that is, eqnirnolecular, interaction t,akes place nearly as rapidly in mixtures of 2 volumes of ethnnc t(’ 1 volume of oxygen.

(5) The second stage, which is also a very rapid one, involves

the breaking down of the original hydrocarbon structure, *6*6*, 2nd

the formation of formaldehyde, carbon monoxide, and steam. This stage may also conceivably be regarded as R process of

hydroxylstion, if we assume the intermediate formation of glycollic acid which immediately decomposes, thus :

. .

That this is a very prominent stage in the sequence of the oxidation phenomena is proved by our circulation experiments. In one of these experiments (No. 5, page 720) as much as 80 per cent., and in another (No. 2, page 717) over 90 per cent., of the ethane burnt appeared in the final products as formaldehyde, carbon monoxide (or i ts oxidation product, carbon dioxide), and steam.

(6) The formaldehyde finally undergoes further oxidation to carbon monoxide, carbon dioxide, and steam, probably as the result of two simultaneous reactions, namely :

c 4H 1 H O (a) 0:b.H +S = O:C*OH = O:C:O+ H*O*H;

[ H 1 H (6) O:b*R+O:O+H*(?:O = 2 O:C*OH = 2CO+2H20.

There was certainly some evidence of the intermediate formation of formic acid in our experiments.

This third stage appears to be somewhat slower than the two preceding stages, a circumstance which, under suitable conditions, leads to a considerable accumulation of aldehyde vapours during an experiment.

(7) Hydrogen, or methane, or both, may appear in the products, without any carbon being liberated, a s the result of the purely thermal decomposition of formaldehyde and acetaldehyde vapours respectively, more particularly when there is a large accumulation of these during a n experiment,. Under the conditions of ou r bulb exyerimentp, we have proved that acetaldehyde does decompose in accordance with the equation CH,*CHO = CH, + CO. Formaldehyde also yields hydrogen and carbon monoxide, although its deccmposition is n more complex process than that of acetaldehyde.

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696 BONE AND STOCKINGS:

(S) A little ethylene and hydrogen may appear in the products RS

t ho result of the purely thermal decomposition of ethane itself :

(9) Carbon is not liberated below the ignition points of the reacting mixtures. If, however, the experimental conditions are such tha t the heat liberated during the initial stages of oxidation is sufficient to raise the temperature of the reacting gases to the ignition point, an explosion occurs, during which the excess of hydrocarbon, and probably aIso aldehyde vapours, 'are decomposed with liberation of carbon and hydrogen, together with some acetylene and ethylene.

(10) The view taken of the mechanism of the combustion of ethane is supported by the experiments on the combustion of ethyl alcohol and acetaldehyde.

C,H, = C,H, + q.

E X P E R I M E N T A L .

PART r. T h e 1 v ) t e r a c t i o n of E t h a n e a n d O x y g e n i n B o r o s i l i c t c t e

G l ~ c s s B u l b s a t T e m p e r a t u r e s b e t w e e n 250Q a n d 400".

Prepai-ation and Conzposition of Original iMixtzcres.

The ethane was prepared by the action of water on zinc ethide mixed mit,h sand; the average yield was about 3 Iitres of gas from every 10 grams of ettiide decomposed, and the purity of the gas is shown by the following explosion analysis :

mm.

27.8)Total 5 45.2. Gas taken ... ... ... ... Oxygen and air added ... 5174

= 3.4." Diluents Explosive mixture

Ratio.. . Contraction (C) Absorption (A) ... ... 55.2

... ..* 69*")C/A = 1.250.

Therefore ethane = 27.6 = 99.3 per cent.

The oxygen was obtained by heating rocrystallised potassium per- manganate. The mixtures of etbane and oxygen were made and stored in graduated glass holders over glycerin diluted with i ts own volume of water; both gasos are practically insoluble in this liquid, and the composition of a particular gaseous mixtiire was not appreciably

* We find it necessary in analysing ethane, or mixtures of ethane and oxygen, to (1ilntc the explosivc mixtiire, 2C,H,+ 70,, with a t least threc timcs its own volume of excess of air or oxygcr~. Otherwise some of the hydrocarbon is decomposed by the shosk of the explosion, carbon is dcpositctl, anti t h e ratio CIA may work out t o 1-30, or cvrn higher, instead of the theoretical 1.250.

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THE SLOW COMBUSTION OF ETHANE. ti97

altered even after prolonged contact with it. Usually, however, the mixtures were used for the experiments within 48 hours of their pre- paration. Most of our experiments were made with mixtures of equal volumes of the two gases, these proportions being, as me found, very favourable to rapid chemical change.

W e also employed mixtures of ethane andoxygen in the ratios 2 : 1 1 : 2, 1 : 3.5, and 1 : 3.75, and in one or two experiments we used mix- tures of ethane and air. The amounts of adventitious nitrogen in our mixtures of ethane and oxygen were always very small, usually less than 0-5, and never more than 1.5 per cent. Following the rule adopted in previous papers, me propose to leave this nitrogen out of the reckoning altogether, and to express the compositions of the various gaseous mixtures, as well as pressure records, in terms of the nitrogen-free gas.” The following table gives the exact com- position of the various nitrogen-free mixtures employed, as well a s the ratio CiA obtained in the analysis of each by the explosiorl method. W e should perhaps add that the oxygen was in each case determined by absorption with a freshly prepared and strongly alkaline solution of pyrogallol, in which we found ethane to be insoluble.

TABLE I.

11 ix ture.

E thane . . , . . . . . . . . . Oxygen ,...........

CIA .................

A. Iu.&c.‘ D. 1 E. __ I

I

_I ___ __ - -

I I

AnaZysis of the Gaseous P?*oducts of Reaction.

The products of reaction usually contained carbon dioxide, carbon monoxide, unchanged ethane, and oxygen. Occasionally also small quantities of aldehyde vapours were present, as well as some methane and free hydrogen. W e found that aldehyde vapours could be removed, without appreciably affecting the relative proportions of the other products, simply by exposing the gases to a thin layer of slrong sulphuric acid for about five minutes.

The carbon dioxide, carbon monoxide, and oxygen were then re-

* Since, in amlysing t h e various mixtures, nitrogen was always estimated ‘ 4 i,y difference,” after all other coiistitueiits had beori determined, t he Iwcentage ~01x1-

position of our nitrogeu-free gases will always add up to 100.

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698 BONE AND STOCKTNGS:

moved and estimabed in the following order, namely : (1) carbon diox ide, by means of strong caustic potash solution; (2) oxygen, by means of freshlyprepared and strongly alkaline pyrogallol solution; (3) carbon monoxide, by agitating for 5 minutes with a freshly prepared ammo- niacal solution of cuprous chloride previously saturated with ethane ; before the final remeasurement, the gas was exposed to a layer of dilute sulphuric acid.* The residual gas mas afterwards exploded with a large excess of oxygen and air, and the ratio C/A determined. A ratio higher than 1.255 was always taken as an indication of the prc- sence of eilher methane or free hydrogen in the products. I n such a. case, a second explosion analysis of the residual gas was usually uiadu after i t had been exposed to the action of ( I oxidised " palladium sponge at loo", in order to determine the relative proportions of methane arid hydrogen present.

The BuEb Experiments at 200° to 400°.

The mixtures of ethane and oxygen were sealed up, a t atmospheric temperatures and pressures, in cylindrical borosilicate glass bulbs which were afterwards kept a t constant temperatures between 200' and 400O. A t the commencement of the reaction the hot gases would, therefore, be under pressuresvarying between 1.75 and 2.33 atmospheres, according to the temperature of the bath. The only departure from the experimental procedure described in a previous paper (Trans,, 1902, 81, 535) was the adoption of a more accurate method of estimating the contraction observed when the cooled bulbs were opened under mercury. After the gaseous products had been removed for analysis through a Topler pump, the bulbs were rinsed out with 2 or 3 C.C. of distilled watcr, and the rinsings tested for aldehydes and acids with Schiff's reagent and litmus respectively.

I n tabulating the results of the various experiments, we shall iu each case give (1) the index letter of the mixture employed; (2) the temperature aad pressure a t which the bulbs were filled ; (3) the duration of heating ; (4) the corrected change in volume (in most cases a con- traction) expressed as percentage of the original volume ; (5) the

* W e adopted this niethod for estimating carbon riionoxide after a sories of trial experiments on the analysis of mixtures of the monoxidc arid ethane in lcnown pro- portions. The solubility of ethane in an animoiiiacal solution of cuprous chloride, although very small, is quite appreciable.

No acstyleiie was ever detected in the products, except in oiie or two of the bulb ox~icIiiiients where the original mixtures of ethaiie slid oxygen exploded. On the other liaiid, t he 1)roducts occavioiially contained ;I. siuall mionnt of ethylene, which would, of course, be reirioved d o n g with thc carbon iiiorioxide by the ninriioiiiacal cuyrous chloride solution. The separate estiiiiatioii of the two gases was always made in a special independent analysis.

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THE SLOW COMBUSTION OF ETHANE 691)

composition of the nitrogen-free gaseous products ; (6) the ratio C/A. found in the explosion analysis of the residual gas after removal of carbon monoxide, carbon dioxide, and oxygen; (7) the ratio CO/CO, in the gaseous products.

Experiments cct 200' and 225".

Four out of six bulbs filled with mixture D (Cj,H,= 49.5 ; O,= 50.5) were kept a t 200--203° for 9 days; there was no appreciable change in any one of them. The other two bulbs were then kept at 225' for a week; the formation of water was observed in one of them after four clays, and in the other a t the end of the experiment. The nitrogen-free gaseous products from the first bulb contained CO, = 1.5, CO = 2.8, C,H, = 4747, and 0, = 48 per cent,, but no hydrogen.*

Experiments at 2 5 0'.

At this temperature, no change WRS observed in the case of three bulbs containing a mixture of 2 volumes of ethane with 1 volume of oxygen after 48 hours. When, however, the gases were mixed in equimolecular proportions, they reacted with fair velocity, which varied considerably with the ' surface factor ' of each bulb. I n one out of five bulbs (No, 1, Table 111) i t will be seen that the whole of the oxygen disappeared within 17 hours, and in another (No. 5) after 48 hours. The reaction was characterised by the continuous formation of steam, and also of aldehydes, as mas evident when we applied Sahiff's test to the rinsings from the bulbs a t the conclusion of each experiment. I n no case was there any deposition of carbon, or liberation of hydrogen, but in all cases the cooled products showed a lLtrge contraction in volume when the bulbs mere open under mercury. Iu bulbs Nos. 1 and 5, about 56 per cent. of the original ethane remained intact at the end of the reaction.

7r 'l'he l o w s t temperature at u h i d i any change could be detcctcd in alixturea of ii~cthaiie a i d oxygeii, siiiiilarly heated in borosilicate glass Lulbs, was 300", aucl ovoll then tl ie hcnting had to be coiitiniiecl for t w o or tliiet: weeks (Tiaus., 1902, 81, 516). P'urther, t he liiilitii~g teinperature at which steal11 is nppreciably formed fiorll electrolytic gas under similar coiiditioiis is about 400".

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700 BONE AKD STOCKINGS:

TABLE 11.

gulbs 1 and 2 mere originally filled with mixture 1; a t 10" and 765 1 1 1 ~ .

,, 3, 4, and 5 9 9

Bulb No. * ..............................

D iiration of heating iu hours . . , . . __

l'erceiitage contraction (corr.) .....

............

............

C/A for ' residual gas ...............

co/co, ....................................

1

17

34.8

15.9 41 :2 nil

42'9

1.250 __--

2-60

,, U ,, 13" and 755 ,,

2 1 3

25

25.7

10-35 23-15 19.10 47'40

__ _ _ -

20 '3

9.25 18.25 25'30 47.20

I 1.250 1 1.250

I

2-23 1 1.97

.

I

4

48

30 '3 _ _

13 .4 29 '3 10.7 46'6

* The formation of condensable intermediate products is proved by the niagnitucle of the contractions observed i n bulbs 1 and 5. For conibiistion to CO, CO,: and H20 only, these contractions would have been 31.7 and 31.9 per cent. respectively.

There was no acetylene in the gaseous products, but, in the case of oiie or two of the bulbs, possibly a small amount of ethylene (under 1 per cent.) was present ; this would be included in the figures for CO.

Since it has been shown tha t no change occurs when the following pairs of gases are kept at 250°, or even a t much higher temperatures, in borosilicate glass bulbs for very long periods of time (Trans., 1902, 81, 53S-593), namely, (u) hydrogen and oxygen (electrolytic gas), (6) methane and oxygen, ( c ) moist carbon monoxide and oxygen, i t may be concluded from the foregoing experiments :

(I) That in the primary oxidation of ethane there is no selective combustion either of carbon or of hydrogen.

(11) That no methane is liberated during the breaking down of the ethane molecule as the result of oxidation pure and simple. This, in view of some later results, is an important point.

(111) That the large quantity of carbon dioxide in the gaseous products did not arise from the secondary oxidation of carbon monoxide,

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THE SLOW COMBUSTION OF' EL'HANE. 701

Experiments at 30 0".

A large number of experiments were made at this temperature with mixtures in which the proportions of ethane and oxygen were varied between 2 : 1 and 1 : 3-75, and the results are extremely interesting from-the point of view adopted in this paper a s to the course of the oxidation. h significant feature was the surprisingly rapid oxidatiou always observed with the mixtures containing ethane and oxygen in the ratio 2 : 1 or 1 : I , as compared with the much slower ratio exhibited by other mixtures containing higher proportions of oxygen,

(I) With Mixtura of 2 Polumes of Ethane and 1 Volume of' Oxygen.

(a) Two bulbp, filled with mixture G at 18" and 760 mm., were maintained at 300' for 30 minutes. On cooling, water condensed on the inner surfaces, and soon afterwards minute oily particles appeared, due, as we afterwards found, to a rapid polymerisation of aldehyde vapoura. No carbm separated. The contractions observed when the bulbs were opened under mercury were 23.6 and 29.3 per cent. respectively. The products contained hydrogen, and probably also some methane. The analytical results are shown in Table 111 (bulbs Nos. 6 and 7).

( b ) I n a second experiment, two bulbs, originally filled a t 1 5 O and 746 mm. with mixture G, were kept at 300' for 45 minutes. The appearance of the cooled bulbs was much the same as in the pravious experiment, except tha t no separation of oily particles was observed. On opening the bulbs under mercury, we were surprised to find no contraction in volume ; if anything, the gaseous products were under slight pressure. There was, however, an overpowering odour of alde- hyde vapours, some of these polymerised in the conneclions of the Topler pump when the gases were withdrawn from the bulbs for analysis. The rinsings from the bulbs gave a strong aldehydic reaction, but we mere unable to detect any ethyl alcohol in them.

Analyses of the gaseous products, after the removal of aldehyde vapours, showed the entire absence of oxygen, and a very high ratio CO/CO,. The ratios C/A obtained for the ' residual gas' in each case (1.616 and 1.650 resp.) indicated the presence of hydrogen, or methane, or both. On again analysing the gas after removal of hydrogen by means of oxidised palladium sponge at loo", the ratio C/A fell to 1,343. Details of this experiment (bulbs 8 and 9) are given in Table 111.

VOL. LXXBV. :' A

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'702 BONE AND STOCKINGS:

TABLE ITT. I

Enlb No. ............................................ ' 6 7 8 ' 9 I I ~ -~

j __-__~

Duration of heating ............................... ' 30 miiis. 30 mins. 45 mins. 45 mins. I I ____ ___ ~- _ -

Percentage contraction (csrr. ) .................. 23 -6 ' 29 -3

Carbon dioxide ......... ...I 3.6 ......... 15.7

' ...................... I Hydrogen

........................

........................ I - - ..................... -

C/A for ' residual gas '... ........................... ~ 1.341

CO/CO, ............................................... / 4.36

1.298

I

I

1.90 36.20 ~

nil 36.50 1 10.20 15.20 ! 1,616 ~

I.

! 19.0 I

I

2-50 35-15

0.20 35.45 10.10 16-60

1.650 - _. -

14.0

The salient features of these experiments aro (1) the very large formation of aldehydes (which in the case of bulbs 6 and 7 polymerised when the hot products were cooled),land (2) in the case of bulbs 8 and 9, the marked production of methane and hydrogen, accompanied ah it was by an extraordinarily high ratio CO/CO,. This formation of methane and hydrogen cannot, as the experiments a t 250° prove, be regarded as the result of the primary oxidation of the ethane; i t is undoubtedly a secondary efFect, connected, it would seem, with an excessive accumulation of aldehyde vapours during the experiment. It may, we think, be entirely ascribed to the purely thermal decompo- sition of acetaldehyde and formaldehyde vapours. W e have proved that under the conditions of our bulb experiments a t 300-400° acetaldehyde does undergo simple decomposition, at a moderate velocity, in accordance with the equation CH,*CHO = CH, + CO. The vapour of formaldehyde also, under similar conditions, decom- poses, yielding carbon monoxide and hydrogen, but the process is not SO simple as the case of acetaldehyde. As one of us is carrying out further experiments on the stabilities of these aldehydes at higher temperatures, we shall reserve details for a future communication.

( 2 ) With Mixtures of Equal YoZumes ef Ethane and Oxygen.

In these experiments, the whole of the oxygen always disappeared within 30 to 45 minutes, and frequently even within 15 or 20 minutes, the

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THE SLOW COMBUSTION OF ETHANE. 703

reaction being marked by the formation of aldehydes, steam, and carbon monoxide, together with smaller preparations of carbon dioxide. Tho ratio CO/CO,, which for similar mixtures at 250' was 1-97 to 2.6 (see Table II), now rose to between 4 and 5. No carbon separated, neither was there any liberation of either hydrogen or methane; the rinsings from the bulbs always had a strong aldehydic reaction. More proIonged heating (see bulbs 12 and 13, Table IV) had little or no effect on the composition of the gaseous products ; the ratio C/A = 1.260 for the residual gas i n the case of bulb 13 suggests the presence of a very small quantity of either hydrogen or methane.

TABLE IV.

ISnlb No.* ...............................

Duiation of heating .................... -

Percentage contraction (cow.). ........

C/A for ' residual gas ' ..................

Ratio CO/CO, ..........................

I l2 10 I 11

_____

45 mins. --

37.6 - __

10-2 47.7 nil

42.1 _ -

1.250

_____- --

4.1

60 mins. lot hours.

38'6 36'8

10'65 9.SO 45'30 48-25 0'45 1 0'20

43-60 41'75

1 '254 1'247 1.249

4.1 4 9

13

23 hoars.

34'4

9 -5 45.0 0 *5

45.0

1.260

_ -

4 '73

* The gases coiitained neither ethylene nor acetylene. The percentagc contraction for these bulbs would have been only about 31 had

the hydrocarbon becn burnt to CO, CO,, and H,O without the forniation of inter- mediate condensable substances.

(3) Vith Mixtures of 1 Volunae of Bihane find 2 Volumes of Oxygen.

The rate of oxidation observed with these mixtures was on the whale distinctly less than in the experiments just recorded. I n one experiment with five bulbs, two (Nos. 14 and 15, Table V) were re moved from the air-oven after 90 minutes, the others were allowed to remain for 16$ hours longer.

Free oxygen still remained in the first two bulbs, but had practically all disappeared from the other three. In no case was carbon deposited or hydrogen liberated; there was an abundant formation of water,

3 A 2

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704 BONE AND STOCKINGS:

carbon monoxide, and carbon dioxide. The rinsings from all the bulbs showed distinct aldehydic reactions.

The ratio C/A for the 'residual gas' after removal of carbon dioxide, oxygen, and carbon monoxide, was always found to be some- what higher than 1.25, and was highest in the case of the bulb which had been heated longest. A second analysis of the ' residual gas,' after i t had been exposed to the action of oxidised palladium sponge at loo", gave ratio C/A not materially different from the corresponding values before treatment with palladium. We therefore concluded that the products contained small quantities of methane rather than hydrogen, and have interpreted the results accordingly. Probably this methane arose as the result of a purely thermal decomposition of acetaldehyde vapour.

The details for three of the above bulbs are given in Table V.

TABLE V.

Bulbs originally filled with mixture H a t 12.5" and 733 mm.

Bulb No ..................................................

Duration of heating ...................................

Percentage contraction (sorr.) ........................

. Carbon dioxide .................. ...............

........................... ...........................

Metlisno.. .........................

C/A for ' residual gaq ' .................................

co/co, ...............................................

_ _ _ _ _ _ _ - - - _ _ - - _ - -

- ~~ -__

14 _-

90 mins. - _

39 -5 ~ ._

18.5 60 '9 15.9 13 9 0.8

1.270 -~

2 -75

15 j 16 I

i 90 mins. I S hours.

I

--,--

35.7 ! 44.5

14-75 1 28-45 34.60 59.10 25'40 ~ 0'20 23.05 I 10.40 2-20 i 1-85

'lie conrlensed water contained aldehydes.

( 3 ) T i th Mixtures of 1 Volume of Ethane and 3; Volumes of Oxpgen.

Although the mixture contained an amount of oxygen just suffi- cient to burn the hydrocarbon completely to steam and carbon dioxide, it is remarkable how very slowly, comparatively, the oxida- tion proceeded. W e never, for example, detected any formation of

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THE SLOW COMBUSTION OF ETHANE. 705

water' within an hour, and even after two days a conaiderable quantity of oxygen, as well as some ethane, remained in the bulbs.

The results for two bulbs, originally filled with mixture K a t 13' and 751 mm., are tabulated below.

TABLE vr.

No. of' bulb ...................................................... ~ _ ~ _ ~ ~- - ________---

D Lira t ion of heat in g ..........................................

Pcrceiitage contraction (corr.) ...............................

Fi

gc.5 A 2 2 & c) G 2 Carbon inoiloxide .......................

Ethane ....................................... b "

5 2 [ Carbon dioxide .......................... g 0 0 0 8% .: 2 2 $ 4 ;i, Oxygeii ...................................

33-30 _ _ _ _

15.05 32'50 44.40

8.05

2-16

37 -0

20.80 36.20 37'50

5 -50

1 '74

The rinsings from these bulbs showed a faint aldehydic reaction with Schiff's reagent, and also i t may be shown by calculation that the original ethane and oxygen a r e not mhoIly accounted For in the gaseous products.

(4) With ci, Mixture oj' I Yolu73a~ 0s Ethane ,with 3.75 Voluwes of Orygat .

Two bulbs, filled a t 13.3' and 760 mm. with mixture L (ethane= Slg05 ; oxygen= 78*95), were kept in the air-bath a t 300' for eight consecutive days. The oxidation was very slow, but eventually all the ethane disappeared. Nearly a third of the original oxygen still remained at the end of the experiEent, the ratio CO/CO, in the gaseous products being 1-28 and 1.31 respectively. The rinsings from the bulb gave a very faint aldehydic reaction. Details of the experiment are given below.

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706 BOKE AKD STOCKINGS:

TABLE VI1.

.............................................. I3ulb No. 19 20 I -__ ~ _ _ _ _ _ -

Diirntion of heating S claj s. 8 d : t p .............................. _ _ .. .......... ..... - - ___.

I'ercentage contraction (corr.) . . . . . . . . . . . . . . . . . ' 3S.1 363.9 _____- ...... ~___.__ - ...................

Y I

..................... 25 #1 26-25 .................. 33.9 ' 33.55

40.20

Carbon dioxide ' 9 g g 2 Carbon monoxidc gz g,E I Oxygen ................................ 1 41.0 v k 1

I %O.A cu ~ 8 o 2

*-_- . ~- -~ ._ -

CO/CO? ..................... .............................I 1-31 1 -2s

Expwirnenls cct 350" to 400'.

These experiments are chiefly interesting in tha t they throw some light on the cause of the separation of carbon during the incomplete combustion of hydrocarbons.

(1) A series ol six bulbs, filled under atmospheric pressure with mixture B (C,H, = 49.S ; 0, = 50-2), were kept in the air-bath at 350' for 40 hours. On withdrawing them, we were somewhat surprised to find their inner surfaces covered with a thick deposit of finely-divided carbon. Some water condensed on cooling, and on opening the bulbs under mercury, we found their contents to be under coneider?ble pres- sure (1000-1 100 mm.). The gaseous products contained much carbon monoxide and hydrogen, as well as smaller quantities of unsaturated lijdrocarbons (including some 0.1 to 0.2 per cent. of acetylene), methane, ethane, and carbon dioxide. The composition of the gaseous products from two of the bulbs is given below.

TABLE V i I L

Bulb No. ..................... 21. ............ 22. Carbon dioxide ............ 4.80 ............ 4.35 Carbon monoxide ............ 33.55 ............. 33.60

Hydrogen.. ................... 4S.80 ............ 50.80 Metbane .................... 8,;s . . . . . . . . . . . . 7-90 Ethane ........................ 1-60 . . . . . . . . . . . . 1 .45

Unsaturated hydrocarbons 2.50 . . . . . . . . . . . . 1 9 0

Evidently, therefore, either the primary oxidation of the ethsue had Liken a different coune a t 350" from tha t indicated by experiments

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THE SLOW COMBUSTION OF EL'HANE. 707

at lower temperatures, or new secondary factors were being brought into play.

(2) The true explanation became clear when the apparatus was so arranged tha t we could watch the bulbs during the whole time of heating, Bulbs containing mixture F (C,H, = 50.3 ; 0, = 49.7) were employed. A bulb was introduced into the bath a t 400' ; the tempera- ture in the vicinity of the bulb immediately sank to 350°, then began to rise rather quickly to about 375", afterwards more slowly. Nothing in particular was observed for a time, but after about four or five minutes, a bright flash mas seen, accompanied by a sharp click and the appearance of a thick cloud of solid carbon particles. The bulb was at once removed. On allowing it to cool, some water condensed, and on nipping off the sealed end of the capillary tube inside a rubber joint connected with a capillary manometer, we found the gases to be under 1290 mm. pressure. The gaseous products, which had much the same composition as those obtained in the previous experiment, are indicated in the following table,

TABLE IX.

BuZ6 X o . 23. Mixture F. Per cent. Per wit .

Carbon dioxide ............... 3.S Methane ............... 5.0 Carbon monoxide ......... 34.3 Ethane ............... 0.9 1 Hydrogen ..................... 54.1 Oxygen ............... 0.4 Unsaturated hydrocarbons 1 *5 -

100.0

The experiment was repeated several times with similar results, which suggested the following view. At temperatures between 350' and 400°, the velocity of the primary oxidation (or of the initial stages of oxidation) is so great that the mixture of ethane, aldehyde vapours, and oxygen, is locally heated to above i ts ignition point (which is probably higher than 400"). The result is an explosion, during which ethane, and possibly also aldehydes, are thermally decomposed with liberation of carbon and hydrogen. If, therefore, the velocity of the initial stage, or stages, could be damped, either by admixture of inert gas, or by using a very slum bulb, the oxidation might proceed nor- mally to its cnd, in which case there should be no liberation of carbon or hydrogen.

(3) Three bulbs, one (No. 24) known to be a very slow one, the other two (Nos. 25 and 26) being quick ones, filled under atmospheric pressure with mixture F, were placed side by side in the same air-bath at 375". The temperature in the vicinity of the bulbs a t once fell to

This was proved in the following experiments,

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708 BONE AND STOCKINGS

350°, then steadily rose during the next 15 minutes to 375". The heating was cmtinued for an hour longer. I n the case of bulbs Nos. 25 and 26, the gases had ignited, and N0.:26 was smashed by the force of the explosion. The inner surface of No. 25 was covered with finely- divided carbon, and water condensed on cooling. The contained gases were under 1100 mm. pressure. I n the case, however, of bulb No. 24, there had been no explosion, and consequently no deposition of carbon ; on cooling it, water condensed on its inner surface, and on opening under mercury there was a contraction of 38.4 per cent.. of the original volume. There was no hydrogen in the gaseous products, but t h e rinsings from the bulb contained aldehydes. Table X shows the details of this very suggestive experiment.

TABLE X.

Bulbs filled with mixture F a t 15" and 750 mm.

Bulb No. ................................................... I I -

Percen tnge change in volume ....................... I I

Carbon dioxide ............ ...............

........................... !

...................... ...;

i

Unsaturated hydrocarhoiis.. . . . .

CIA for < residual gas ' ................................. ;

24

- 38 s o *

_ _ -

8.15 52.35 39-50 nil. nil. uil.

1.250 __-

Ratio CO/CO,.. ........................................ ...I 6'42

25 I 26

$46 I 4.75 1 Bulb

33.30 sinashed 1-35 j by tlie

50.90 i force I 9 0 of the 1-80 , exldosiou.

* For coinbustion t o CO, CO,, and H,O only, without the formation of condensable intermediate products, this would only have been - 30.8.

(4) We now damped the velocity of oxidation by diliition with nitro- gen. Two bulbs, Nos. 27 and 28, were filled with mixture B (ethane = 49-S ; oxygen = 50.2) diluted with about 8 per cent. of nitrogen. Two other bulbs, Nos. 29 and 30, were filled with tt special mixture of ethane aud air cont.aining C2116 = 16.95 ; 0, = 17.40 ; and N, = 65.65 per cent. Bulb 27 was kept a t 390-400" for an hour, :tnd No. 28 at the same temperature for 18 hours. Bulbs Nos. 29 and 30 we10 kept at 380-390" for 24 hours. The oxidation proceeded normally in all C:LSOS ; all the oxygeu disappeared, water and aldchgdes were formed, but there was

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THE SLOW COMBUS'I'ION OF ETHANE. '709

neither separation of carbon nor liberation of hydrogen. of the experiments with bulbs Nos. 27 and 20 are given below.

The details

TABLE XI.

Eulb No. ............................................................ 27 29

Durntioii of heating ........................................... 1 honr . 2 4 hours

Percentage contractioii (COIT. ) ................................ 35 I 15

Carbon dioxide ............................... 7 -20 5.90 ......................... 7.70

........................................ 0.10

......................................... 11*50 Nitrogeii .................................... I ~ L - ~ O 74.80

44.20 9.10

36.10

C/A for 'residual gas' ..................................... i 1.260 1 1.250 -

- 1 _ _ . ~ ~ ________---

CO/CO, ............................................................ 6'14 1 1-30

W e would draw attention to the ratios CO/CO, observed in these bulb experiments, the conditions of which precluded the possibility of the independent oxidation of carbon monoxide.

If we consider the experiments in which the combustion proceeded quite normally, tha t is to say without any secondary decompositions of aldehyde vayours or of the excess of hydrocarbon, we find tha t for one and the same original mixture of ethane and oxygen the ratio CO/CO, in the products is higher the higher the temperature, and there- fore nIso the higher the velocity of the oxidation. Thus, for the original mixtures of equal volumes of ethane and oxygen, a t 250' the ratio CO/CO, varied between 1 *97 and 2.60; a t 300°, between 4.1 and 4.9 j and in each of the two bulbs a t 350° i t exceeded 6.0. These observations are quite consistent with the view of the oxidation stages set forth in the introduction of this paper, namely, that carbon monoxide arises in the second stago as the result of the oxidation of acetaldehyde, CH,*CHO + O2 = CH,O + CO + H20,as well as during the final oxidation of formaldehyde in the third stage, in which the two simultaneous reaction,s : (CG) CH,0 + 0, = CO, + H20, aud ( b ) C H 2 0 + 0, + CH,O =

2CO + 21I,O, are concerned. Again, in the experiments a t W O O , in which the poportioils of

ethane and oxygen in the mixtures eruylujed varied between 2 : 1 and 1 : 3.75, the ratio CO/CO, in the productk naturally decreabed with

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710 BONE AND STOCKINGS:

the higher proportions of oxygen originally present. But it is a significant fact,and one quite explained by our theory of the oxidat ion stages, tha t even when the oxygen in the original mixture was more than suffi cient to burn all the ethane completely to carbon dioxide and steam, the ratio CO/CO, in the products did not full below 1.25.

PART IT.-Experiments witlh M i x t u r e s of E t h a n e a n d O x y g e n i n the Circulcc t ion A p p a y a t u s .

These experiments were undertaken primarily for the identification of the aldehydes, and possibly other condensable or soluble intermediate oxidation products, the formation of which had been proved in the bulb experiments. The circulation apparatus has already been fully described in a previous paper on methane (Trans., 1903, 83, 1074), and is here represented in Fig. 1. Since the experimental method with ethane was, in all essential respects, the same as witb methane, we may a t once proceed to the discussion of our new results. It was first of all necessary to ascertain whether ethane itself would undergo any change under our experimental conditions. Accord- ingly we circulated the pure gas in the apparatus for three consecutive days, the temperature of the combustion tube being kept at 500' throughout. A slight expansion (about 4 mm. on 500) was noticed and a subsequent analysis of the gas showed tha t it contained about 1 per cent. of ethylene and some hydrogen. Thus the values C/A obtained in two explosion analyses of the residual gas after removal of ethylene by means of fuming sulphuric acid were 1.267 and 1.266 respectively. There was no deposition of carbon on the white, porous porcelain with which the combustion tube was packed.

Ident$cation of Intermediate Pwducts.-Among the possible soluble and condensable products which could be caught up by the water in the worm E (Fig. 1) were ethyl alcohol, glycol, glgoxal, acet- and form- aldehydes, acetic and formic acids. I n all our experiments, the liquid had a strong aldehydic smell, reminiscent more of formaldehyde than of acetaldehyde ; it reacted strongly with Schiff's reagent, and instantly reduced ammoniacal silver solutions, The liquid was usually quite neutral to litmus, although occasionally it had a distinct acid reaction, due to the presence of small quantities of formic acid, and possibly also of acetic acid. After dilution with an equal volume of water, it was submitted to the following tests.

( 1 ) Y'he Iodofomr?. Yest.-Ethyl alcohol or acetaldehyde would, of course, give thip, but whereas the iodoform precipitated from a dilute acetaldehyde solution is always amorphous, tha t which separates f rolu dilute solutions of ethyl alcoholis nearly always composed of the char- acteristic star-like, crystalline aggregates. Occasionally the liquid we

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THE 81BW COMBUSITON OF ETHANE. 711

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71 2 BONE AND STOCKINGS:

obtained gave amorphous iodoform, but we never got the least indica- tion of a crystalline precipitate. When iodoform was obtained, we repeated the test with another portion of the liquid after i t had remained in contact with dilute caustic soda, to polyineriee the alde- hydes, and subsequently distilled in steam. We never detected any ethyl alcohol in the distillate. I n some cases we removed the alde- hydes by careful oxidation, at the ordinary temperature, with a slight excess of an ammoniacal silver solution. The liquid was subsequently acidified with dilute sulphuric acid and distilled in steam, but alcohol was never detected in the distillates.

(2) Reaction with an Acetic Acid Solution of p-B1.omophenylhydra2ilze.- The aldehydes present could generally be recognised by an examination of the resulting canary-yellow p-bromophenylhy drazones. I n this way the presence of formaldehyde was always detected, and sometimes tha t of acetaldehyde also, but there was never the faintest sign of the separation of the deep-red p-bromohydrazone of glyoxal.

( 3 ) Reaction with Hydrogen 8uZphide.-The liquid, without any addi- tion of bydrochloric acid, was saturated with hydrogen sulphide and the test-tube set aside in a warm place for several hours. By this means form- and ncet-aldehydes may be distinguished with the greatest certainty (Proc., 1904,20, 115). We invariably obtained the character- istic white flocculent precipitate of the thio-derivative of formaldehyde.

(4) I n some cases, a portion of the liquid was slowly evaporated to dryness in a glass basin over a water-bath. There was never any indication of the separation of glyoxal during the process, or of any solid residue. Once or twice the faintest possible greasy film remained.

Briefly, khen, the most prominent and constant intermediate product formed in these experiments was formaldehyde, which was frequently accompanied by smaller proportions of acetaldehyde and, in one or two cases, by traces of formic acid also. There mas no direct evidence of the formation of any other intermediate substance such as ethyl alcohol, glycol, o r glyoxal.

Details of Experinzents.

Pollowing the plan of our earlier paper on methane (Zoc. c i t . , p. lOSl-lOS7), we propose to give: (I) the pressure of the dry nitrogen-free mixture, a t the temperature to of the room, introduced into the cold apparatus, (2) its pressure after tho furnace had beeu lighted and the combustion tube raised to the experimental tempera- ture, To, (3) the ' corrected ' pressures of the dry nitrogen-free gases in the apparatus at successive regular intervals of time, (4) the pressure of the dry nitrogen-free products a t the end of the experi- ment, after the furnace had been turned out and the apparatus

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THE SLOW COMBUSTION OF ETHANE. 713

allowed to cool down to the temperature of the room, and ( 5 ) the composition of the gaseous products, together with the ratio C/A, obtained in the explosion analysis of the residual gas after removal of the oxides of carbon, oxygen, a r d any small amount of ethylene which might be present,

The gases mere continuously circulated, day and night, over the hot surface of the porous porcelain in the combustion tube a t a constant rate throughout each experime2t. This rate was, of course, varied in different experiments, but it may be assumed that the time required for a complete circuit varied between 30. minutes and about 2 hours. This circumstance explains the different rates of oxidation observed with similar mixtures of ethane and oxygen.

The capacity of the whole apparatus was about 1500 c.c., that of the combustion tube was only 75 C.C. Since, however, the temperature of the combustion tube was 450-500°, whereas that of the rest of the apparatus was only 20-25', it follows that not more than 1/50th of the total gas in the apparatus was in the heated zone a t any one time. But, further, since i t has been proved during the research tha t chemical change is mainly, if not entirely, confined to the layer of gas immediately in contact with the porous surface, i t follows tha t very much less than 1150th of the total gas was, at any one instant, actually in the sphere of reaction; a t the very most not more than 1/100th of the whole gas would be reacting at any given instant. Hence the rates observed in these experi- ments must be multiplied by at least 100 to give us even an approximate idea of the actual rates of charge within the sphere of reaction. I t must also be borne in mind that the conditions of these circulation experiments, unlike those of the bulb experiments, admil; of the fairly rapid oxidation OF free hydrogen as well as of carbon monoxide.

( I ) Experiment with Equcd P%lumes of Ethane and Oxpgen at 450".

This experiment extended over 10 consecutive days, the speed of circulation was ~clow, the capillary tubes in GHK (Fig. 1) being in circuit throughout.

Pressure of cold d;y nitrogen-free

Pressure of cold dry nitrogen-free

Mixture E (C,H, = 49.7 ; 0, = 50.3) was used.

original mixture a t 18.3" ............ = 628.4 mm.

final products a t 18.3' ............... = 428.1 mm.

Total pressure fall = 200.3 mm. or 31 *9 per cent.

The daily records were as follows :

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71 4 BONE AND STOCKINGS

Temperatnre of Temperntiire of Corrected pressnre of DRYS. coml~nstion tube To. glohe 1". (1 ry 11 i t mgen- frec gas.

0 ............ 450" ............ 2 l 0 . . . . . . . . . . . . 651.3 mm. 1 ............ 452 ............ 22 ............ 632.6 ), 2 ............ 460 . . . . . . . . . . . . 20.5 ............ 590 0 ,) 3 ............ 450 ............ 209 . . . . . . . . . . . . 561.2 ),

5 . . . . . . . . . . . . 449 ............ 19.0 ............ 516.2 ,, 6 ............ 451 ............ 19.3 ............ 49S.7 ,, 7 ............ 440 ............ 19 6 ............ 480.8 ,, 8 . . . . . . . . . . . 446 ............ 20.0 ............ 460.8 :, I) ............ 455 ............ 18.7 ............ 455.1 ,,

10 ............ 450 ............ 18.0 ............ 449.3 ,,

4 . . . . . . . . . . . . 447 ............ 17.7 ............ 538.8 .,

The pressure curve for this experiment (Fig. 2, Curve J, ordinates= pressures, abscissa = time in days) shows tha t the pressure fall was

FIG. 2.

650

600

550

500 ; p 5 450

E w

400 - + - + 'E 3E0

z g e

300

250

200

150

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THE SLOW CONBUSTION O F ETHANE. 71 5

very regiilar during the first 8 days, but slackened towards the end of the experiment.

There was no sign of any deposition of carbon on the white porous porcelain during the experiment; this remark applies also to all the other circulation experiments described. The gaseous products still contained some oxygen, considerable quantities of carbon mon- oxide and dioxide, as'well as about 1 per cent. of ethylene and some hydrogen. The ratio C/A for the 'residual gas ' was 1-30? which after treatment with palladium fell to 1.25. The mean of three concordant analyses gave the following as ths percentage composition of the nitrogen-free gaseous products :

Carbon dioxide ... 19.90 Ethylene ............ 1.00

Oxygen ............ 4.85 Ethane ............... 46.80 Carbon monoxide.. 24.45 Hydrogen ............ 3.00

The liquid in the worm had an aldehydic odour and reaction, but was quite neutral to litmus. It contained formaldehyde, some acetaldehyde, but no ethyl alcohol.

If we now compare the partial pressures of the ethane and oxygen in the original mixture with those of the various gaseous products at the end of the experiment, we obtain the following numbers :

Original Mixture.

Ethane ...... 312.4 mm. Oxygen ...... 316.0 mm.

Products.

mm. mm. Carbon dioxide ......... 85.2 Ethane ............ 200.4 Carbon monoxide ...... 104.7 Ethylene ......... 4.3 Oxygen .................. 20.7 Hydrogen ......... 12.8

The 4.3 mm. of ethylene probably arose from a thermal decomposition of a corresponding quanhity of ethane ; the 1 2 4 mm. of free hydrogen may be partly ascribed to the same cause, possibly also in part to the thermal decomposition of formaldehyde vapour. The above figures show that 107.7 mm. of ethane had reacted with 295.3 mm. of oxygen, yielding altogether 189.9 mm. of carbon monoxide and dioxide.

(2) Experiment with Equal VoZurnts at 500O.

For t,his, which, in respect to the amount of aldehydes removed from the sphere of action, is the most remarkable of all our experi- ments, mixture E (C,H, = 49.7 ; 0, = 50.3) was used.

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716 BONE AND STOCKINGS :

Pressure of cold dry nitrogen-free original mixture a t 17.5" ......... = 467.6 mm.

Pressure of cold dry nitrogen-free final products at 17.5 O......... ...... =363.4 mm.

-- Fall =204.2 mm., or 43.66 per cent.

The experiment extended over three consecutive days, the tempera- ture of the combustion tube remaining very constant throughout. A rapid rate of circulation was kept up by throwing the capillary tubes in GHK (Fig. 1) out of circuit and allowing the Sprengel pump to work at full speed.

The daily records were as follows :-

Temperature of Tempernture of Corrected pressure of Days. combustion tube. globe A. dry nitrogen-free gas.

0 ........... 500' ............ 21.3' ......... 490.7 mm. 1 ............ 503 ............ 20.8 ......... 416.0 2 ............ 500 ............ 21-7 ......... 344.3 3 ............ 503 ............ 21.5 ......... 276.3

Tho pressure curve for this experiment (Fig. 2, Curve 11) is an un- broken straight line.

The liquid in the worm had a distinctly acid reaction and a very strong aldehydic odour. It did not give the iodoform reaction, and therefore contained neither ethyl alcohol nor acetaldehyde. The p-bromophenyl- hydrazone prepared from i t was identical with tha t of formaldehyde.

Eesides carbon monoxide, carbon dioxide, and unchanged ethane, the gaseous products contained a considerable quantity of oxygen, some hydrogen, and ethylene. The ratio C/A for the residual gns was 1,269, and the percentage composition of the gaseous products mizs as follows :

Per cent. Per cent. Carbon dioxide,. ....... 20.96 Ethylene ............ 2.75

Oxygen ............... 8.00 Ethane ............... 51-00 Carbon monoxide ... 16-00 Hydrogen ......... 1.30

Comparing, again, the partial pressures of the original gases with those of the final products, we have :

Original Mixlure. Ethane ...... 232.5 mm. Oxygen ...... 235.1 mm.

P~oducts. mm.

Carbon monoxide ...... 42.1 Ethylene Carbon dioxide ......... 55.2 Hydrogen Oxygen .................. 21.1 Ethane ..

R i m .

............ 7.2

............ 3.5

............ 134.4

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THE SLOW COMBUSTION OF ETHANE. 717

These numbers show tha t whereas 90-7 mm. (that is, 232*5rninus134*4 and 7-2) of ethane had been oxidised during the experiment, the sum of the pressures of carbon monoxide and dioxide in the products only amounted to 97.3-mm., a circumstance which points to a very large formation of formaldehyde according to the empirical equation :

C,H, + 20, = CO + CH20 + 2H20.

Assuming this to have taken place, then, from the total ethane oxidised and the total oxides of carbon formed, we calculate tha t no less than 84.1 mm., or 92.7 per cent., of the ethane oxidised appeared in the products as formaldehyde, carbon monoxide (or dioxide), and steam, the remaining 6.6 mm. being completely oxidised to carbon dioxide and steam. Undoubtedly by far the greater part of thecarbon dioxide produced in the experiment arose from the independent oxidation of carbon monoxide.

We will now show tha t the foregoing conclusion agrees very well with the amount of oxygen which actually disappeared during the experiment, namely 214 mm.

84.1 mm. C,H, oxidised to CO + CH,O + 2H,O

6.6 mm. C2H6 oxidised t o 2CO+3H20 would require ................................. 168.2 mm. 0,.

would require ................................. 16.5 mm. ,, 27.6 mm. ,, 65.2 mm. GO oxidised to GO, would require ...

Total ......... 212.3 mm.

(3) Experiment witlh Equal Volumes at 500'.

within 8 hours. used.

Pressure of cold original mixture

Pressure of cold final products at

This is interesting chiefly on account of the extremely rapid rate of oxidation observed, nearly the whole of the oxygen disappearing

Mixture D (ethane = 49.5 ; oxygen = 50.5) was

dry nitrogen-f ree a t 17.8' ............ = 434.6 mm. dry nitrogen-f ree

17.8' ............... =292*0 mm, --

Pressure fall = 142.6 mm., or 32.8 per cent.

The pressure record8 were as follows :

VOL. LXXXVK.

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718 BONE AND STOCKINGS:

Time in Temperature of Temperature of Corrected pressure of dry hours. combustion tube T". the globe to. nitrogen-free gases.

0 ......... 5103 ......... 23.2" ............ 460.3 mm 1 ......... 509 ......... 25.0 ............ 415.0 2 ......... 499 ......... 25-0 ............ 384.0 3 ......... 500 ......... 26.0 ............ 353-8 ,,

8 ......... 510 ......... 2 6 5 ............ 300.0 ,,

24 ......... 604 ......... 24.S ............ 310.0 ,,

4 ......... 503 ......... 26-0 ............ 324.0 ,,

11 ......... 505 ......... 26.5 . . . . . . . . . . . 295-4 ,,

The pressure curve for this experiment is shown in Fig. 3, Curve 111. It will be observed that n slight expansion occurred after the eleventh

FIG. 3.

500

k 7 400 s s

.X, 350

250 0 2 4 6 8 1 0 1 2 1 4

Time in, hours .

16 18 20 22

hour, the pressure fall up to that time being 35.8 per cent. This expansion must be attributed to the decomposition of acetaldehyde papour, for there was a considerable accumulation of aldehydes during the experiment, and the gaseous products contained an unusually large quantity of methane.

The liquid in the worm contained acetaldehyde and formaldehyde, but no ethyl alcohol or glyoxal.

The nitrogen-free products contained nc, free oxygen, and had the following composition :

Pcr cent. l'er cent. Carbon dioxide ......... 35.1 Methane ......... 8.8 Carbon monoxide ...... 10.3 Hydrogen ...... 1.8 Ethylene ............... 2.2 Ethane ......... 41'8

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THE SLOW COMBUSTION OF ETHANE. 719

The ratio C/A for the residual gas, after removal of the oxides of carbon and ethylene, was 1.35, -which after further treatment with oxidised palladium at 100' was reduced to 1.32.

(4) Experiment with u Mixture of Ethane and Air at 500'.

This experiment was performed in the hope that by largely diluting the reacting gases with nitrogen we might possibly detect the forma- tion of ethyl alcohol, and also prevent any secondary decompositions of ethane and aldehyde vapours.

The mixture used contained ethane = 15.80 ; oxygen = 17.65 ; and nitrogen = 66.55 per cent. The experiment extended over three days, but the oxygen had practically all disappeared at the end of the second day.

Pressure of cold dry original mixture a t 12.5' = 46752 mm. $ 9 ,, ,, final products ,, ,, = 398.2 mm.

Fall = 69.0 mm.

This pressure fall is 14.75 per cent., or approximately 44.5 per cent., of the pressure of the original nitrogen-free mixture. The daily records were as follows :

Temperature of Temp-ature of Corrected pressure Days. combustion tube To. globe to. of dry gas at 25". 0 ............ 494' ............ 22.0' ............ 511.0 mm. 1 ............ 500 ............ 25.5 ............ 449.0 ,, 2 ............ 500 ............ 25.0 ............ 424.4 ,, 3 ............ 500 ............ 25.2 ............ 423.4 ? ?

The curve for this experiment is shown in Fig. 2, Curve IV. The liquid in tho worm contained acetaldehyde and formaldehyde,

but no ethyl alcohol. The gaseous products contained only carbon dioxide, carbon

monoxide, unchanged ethane, and nitrogen. The ratio C/A for the residual gas was 1.249, showing the entire absence of free hydrogen or methane. Evidently, therefore, dilution with nitrogen had entirely prevented secondary decompositions of ethane and aldehydes. The percentage composition of the gaseous products was :

Carbon dioxide ......... 7.00 Ethane ...... 10.50 Carbon monoxide . , . , . . 4.10 Nitrogen ... 78.4

We calculate that in this experiment about 10 per cent. of the ethane changed appeared in the products as acetaldehyde and steam, 40 per cent. as formaldehyde, carbon monoxide (or dioxide), and steam and that the remainder had been completely burnt t o carbon dioxide

3 s 2

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720 BONE AND STOCKINGS

and ateam. of formaldehyde had undergone independent oxidation.

Some of the carbon monoxide liberated in the formation

(5) Experiment with Mixtuw of 1 Volume of Ethane to 2 Volumes of Oxygen at 500O.

For this experiment, which extended over a week, mixture The speed of circulation was H (C,H, = 32.2 ; 0, = 67.8) was used.

fairly rapid throughout.

Pressure of the cold dry nitrogen-free original mixture at 17O ...................

Pressure of the cold dry nitrogen-free = 468.9 mm.

= 176.8 mm.

Fall = 292.1 mm.

final products at 17" ..................... --

This pressure fall is 62.3 per cent. of the original pressure. The curve for this experiment (Fig. 2, Curve V) indicates a fairly rapid oxidation during the first two days, followed by a much slower process. The portion of the curve for the latter part of the experiment resembles curves we have obtained for the oxidation of moist carbon monoxide, and it will be seen that carbon dioxide predominated in the gaseous products. The daily records were as follows :

Temperature of Temperature combustion tube of globe Corrected pressure

Days. T". to. of dry nitrogen-free gas. 0 ......... 500" ......... 18.5" ......... 502.0 mm. 1 ......... 499 ......... 25.6 ......... 387.4 ,, 2 ......... 496 ......... 26.8 ......... 295.4 ,, 3 ......... 496 ......... 26.8 ......... 269.9 ,, 4 ......... 484 ......... 27.5 ......... 235.3 ,, 5 ......... 494 ......... 27.8 ......... 207.4 ,,

'7 ......... 487 ......... 26.3 ......... 185.7 ,, 6 ......... 493 ......... 27.3 ......... 188.1 ,,

The liquid in the worm had a slightly acid reaction; it coutained a The gaseous mere trace of acetaldehyde, but much formaldehyde.

products contained : Per cent. Per cent.

Carbon dioxide.. ....... 6 1-40 Ethane.. .... 13-40

Oxygen .................. 0.55 Hydrogen.. . 0.45 The ratio C/A for the ' residual gas ' was 1.273.

Carbon monoxide., . , . . 23.20 Ethylene ... 1.00

Comparing now the partial pressures of the original mixture with those of the gaseous products as under :

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THE SLOW COMBUSTION OF ETHANE. 721

Original Mixture.

Ethane ......... 151.0 mm. Oxygen ......... 317.9 mm.

We

Pinat Products.

mm. mm. Carbon dioxide ......... 10S.6 Ethane.. .... 25.70 Carbon monoxide ...... 41.0 Ethylene . . , 1-75 Oxygen .................. 1.0 Hydrogen,. . 0.75

find that whereas 125.5 mm. of ethane underwent oxidation during the experiment, the sum of the pressures of carbon monoxide and dioxide in the products amounted to 149.6 mm. only. We estimate that approximately 80 per cent, of the ethane oxidised appeared in the products as formaldehyde, carbon monoxi,de (or dioxide), and steam, the remainder being completely burnt to carbon dioxide and steam.

(6) Expsrinzents with Mixtures of 2 Volumes of Ethccne to 1 Volume of Oxygen.

Having failed to detect any ethyl alcohol among the products of the foregoing experiments, we proceeded t o investigate the interaction of mixtures of ethane and oxygen in the ratio 2 : 1. Since rapid combination is the most favourable condition for the isolation of intermediate products, we circulated these mixtures at top speed, keeping the temperature of the combustion tube a t 500'. Under these circumstances, nearly the whole of the oxygen disappeared within 12 hours, a rate hardly inferior to that observed under similar conditions with mixtures of equal volume (Expt. 3, page 717). We also tried experiments at lower temperatures (350O and 40Q0), but the rate of combination was much slower. In none of these experiments, however, were we able to detect any production of ethyl alcohol. As we need only give the details of one of these experiments, we will select a case in which the products were found to contain a fair quantity of hydrogen. Mixture G was used (ethane = 66.65 ; 0, = 33-35}, and pressure readings mere made every two hours during the early part of the experiment.

Pressure of the cold dry nitrogen- free origir?al mixture at 17" ......

Pressure of the cold dry nitrogen- free final products at 17 "... .........

=470*4 mm.

= 370.0 mm.

Fa11 ...... = 100.4=21.35 per cent.

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722 BONE AND STOCKINGS:

The records were as follows :

Hours. 0 ..

Temperature of Temperature the combustion tube of the globe Corrected pressure

T" to. of dry nitrogen-free gas. .......... 480' ............ 22.2' ............ 514.0 mm.

2 ............ 490 ............ 25.2 ............ 494.0 ,, 4 ............ 493 ............ 23.7 ............ 476.0 ,, 6 ............ 492 ............ 24.2 ............ 455.8 ), 8 ............ 490 ............ 24.8 ............ 435.0 ,)

10 ........... 492 ............ 26.3 ........... 419.2 ,) 12 ............ 494 ............ 25.9 ........... 409.0 ,, 24 ............ 492 ............ 26.6 ............ 39S.S ,,

Thecurve for this experiment is shown in Fig. 3, Curve VI. The liquid in the worm was quite neutral to litmus and contained

acet- and form-aldehydes, but no alcohol. The gaseous products contained :

Per cent. Per cent. Carbon dioxide ... 12.46 Ethane ............... 57.10 Carbon monoxide.. . 15.00 Methane ............ 2.30 Oxygen ........... 0.30 Hydrogen ......... 12%

The ratio C/A for the residual gas was 1.430, which after removal of hydrogen by means of oxidised palladium sponge at 100°, was re- duced to 1.265.

With regard to the other experiments with these mixtures, we may perhaps briefly refer to one in which the combustion tube was packed with fragments of fused quartz instead of the usual porous porcelain, because it illustrates in a striking manner the dependence of the velocity of oxidation on the character of the heated surface employed. I n the experiment in question, although the temperature of the combustion tube was maintained at 480-500°, and the pump worked a t top speed throughout, the pressure of the gases in the apparatus (measured cold and dry) only fell from 41'7.5 mm. to 384 mm., or by about 8 per cent., in four days, a rate of reaction only about one-tenth that observed under similar conditions with a catalytic surface of porous porcelain.

PART 111.-Experiments on t lhe S l o w C o m b u s t i o n of E t h y l A l c o h o l a n d A c e t n Z d e h y d e .

A. Ethyl AZcohoZ.

Assuming, for the moment, that the initial stage in the oxidation of ethane involves the formation of ethyl alcohol, the non-occurrence of this compound among the soluble intermediate produots in our cir-

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THE SLOW COMBUSTION OF ETHANE, 723

culation experiments would be explained if it could be shown that, under similar conditions, alcohol reacts with oxygen much more rapidly than does ethane itself. It was also important to ascertain whether or not the intermediate stages of the oxidation of alcohol are of the same character and sequence as those of ethane, namely : (1)* formation of acetaldehyde and steam, and (2) formation of earbon monoxide, formaldehyde, and steam.

As i t was not feasible to use the circulation apparatus for these ex- periments, we set up a special apparatus in which air o r oxygen could be passed at a constant rate (about 1; litres per hour) through (1) a series of glass worms containing pure ethyl alcohol kept a t a definite temperature (to) in a large water-bath, (2) a combustion tube packed with porous porcelain, of the same dimensions as the tube used in the circulation apparatus, heated to a constant temperature (TO), and (3) two worms containing water, and externally cooled by water for the removal of soluble intermediate products. Arrangements mere also made for the collection of samples of the exit gases. The con- ditions of these experiments were therefore fairly comparable with those of the etbane circulation experiments, except that of course in the latter the reacting gases passed many time8 over the heated surface. Our object was to ascertain the limiting proportion of alcohol vapour which could enter the combustion tube without any of i t surviving 4 single passage over the heated surface.

The vapour pressures of alcohol at the various saturation tempera- tures employed are as follows :

t, 10". 20". 30". 40". 50". p , 84.2 44.5 78.5 134.0 220.0 mm.

(a) Expeiimenta with Air.

(i) Wi th the furnace at 300°, traces of alcohol appeared in the products with a saturation temperature of 20°. The liquid in the worm contained acetaldehyde but no formaldehyde. The exit gases contained a trace of carbon dioxide and 18.7 per cent. of oxygen,

(ii) Wi th the furnace a t 350°, no alcohol survived the passago through the combustion tubs with a saturation temperature of 30°, but it appeared in the exit gases with a saturation temperature of 30°. The products contained much acetaldehyde and also some form- aldehyde, and the gases from one experiment (saturation temperature 20°) contained : CO,= 1.9 ; CO = 2.8 ; and 0, = 13.8 per cent.

(iii) Wi th the furnace at 500°, no alcohol survived a single passage over the heated surface at all saturation temperatures under 35*, but it appeared in the exit gases when the saturation temperature was 40'. The liquid in the worms now had a faintly acid reaction,

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724 BONE AND STOCKINGS:

and contained both acetaldehyde and formaldehyde. The gaseous products from one experiment (saturation temperature = 40') contained C 0 2 = 5 * 5 ; c0=12*0; 0,=ni1; C,H4=1*5; CH4=4*0 per cent.

All the foregoing oxidation rates are far in excess of those observed with ethane at corresponding temperatures in the circulation apparatus.

( 6 ) With u Mixture of Oxygen = 48.6 per cent. and Nitroyen = 51 -4 per cent.

With the furnace a t 425O, the ingoing gas was sometimes saturated at 50' even without alcohol appearing in the exit gases. The liquid in the worms, which was neutral to litmus, contained acetaldehyde and much formaldehyde, but no glyoxal. The gaseous products from one experiment (saturation temperature = 40') contained : GO, = 3.1 ; CO = 8.5 ; 0, = 35.1 ; and CH, = 0.8 per cent.

( c ) With 95 per cent. Oxygen.

(i) With the furnace a t 450°, and the gas saturated a t 30°, no alcohol escaped from the combustion tube. The liquid in the worms had a faintly acid reaction; it contained acetaldehyde and much form- aldehyde, but no glyoxal. The gaseous products contained : CO, = 3.7 ; CO = 13.0 ; 0, = 77.0 per cent.

(ii) Wi th the furnace at, 450°, and the gas saturated a t 50°, a mere trace of the alcohol vapour survived the passage over the heated surface. The liquid in the worms, which had a distinctly acid reaction, contained acetaldehyde and formaldehyde, but no glyoxal. The gaseous products contained : CO, = 6.0 ; CO = 12.8 ; 0, = 76.4 ; 02H, = 0.3 ; CH, = 0.3 ; N, = 4.2 per cent.

The conclusions, therefore, t o be d rawn from these experiments are : (1) That ethyl alcohol reacts with oxygen far more rapidly than

does ethane itself under similar conditions. (2) That its oxidation stages, like those of ethane, involve the suc-

cessive formation of (a) acetaldehyde and ( b ) formaldehyde, together with considerable quantities of carbon monoxide.

B. Acetu Zdehyh.

It finally remained to show tha t acetaldehyde and oxygen react in our circulation apparatus forming formaldehyde in conformity with the views expressed in the earlier part of this paper. The experimental method was as follows.

Jus t sufficient water was introduced into the globe of the apparatus to keep its inner surface wet during the experiment ; about 20 C.C. of

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THE SLOW COMBUSTION OF ETHANE. 7 25

water were put into the worm. The apparatus was then completely exhausted of air, the furnace lighted, and the combustion tube raised to the desired experimental temperature. Moist oxygen was then admitted into the apparatus until the manometer recorded a pressure of about 250 mm. The oxygen supply having been cut o f f , connection was made with a small distillation flask containing acetaldehyde ; the air in the flask had been previously completely expelled by the vapour of the boiling liquid. The vapour of the acetaldehyde was then slowly admitted to the apparatus until the manometer indicated a further fall of about 300 mm.

The mixture of aldehyde vapour and oxygen was then rapidly circu- lated, pressure records being taken a t frequent intervals. Finally, a sample of the gaseous products was withdrawn and analysed after any aldebyde vapours present had been polymerised and removed by contact with a layer of pure sulphuric acid. The liquid in the worm was also carefully examined for formaldehyde.

1st Experim<ent,

Pressure of oxygen (dry) originally admitted = 250 mm. ,, ,, aldehyde vapour ,, = 291 ,, $ 9 --

Total = 541 ,, There was a fairly rapid pressure fall in the apparatus during the

first hour and a half, but during the next hour hardly any further fall was observed. This stationary period was succeeded by a very gradual rise in pressure, which was maintained on continuing the circulation overnight.

The records obtained were as follows :

Temperature of Corrected lwcssure Time in combustion tube for dry hours. P. mixture.

0 .................. 451' .................. 541 rum.

24 .................. 461 .................. 462 ,, 34 .................. 459 ................. 471 ,, 54 .................. 460 .................. 474 ,, 74 .................. 464 .................. 481 ,,

S l g .................. 474 .................. 504 ,,

14 .................. 460 .................. 462 :,

The liquid in the worm was nearly neutral to litmus and contained much formaldehyde ; during the experiment, also, .a small quantity of a white solid, apparently paraformaldehyde, appeared on the surface of the globe A.

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726 BONE AND STOCKINGS:

The gaseous products had the following percentage uomposition :

Carbon dioxide ......... 23.5 Methane ......... 23-35 Carbon monoxide.. .... 47.1 Hydrogen.. ..... 4.45 Oxygen .................. nil Nitrogen ........ 1.60

From the large proportion of methane present it is evident that a considerable amount of the acetaldehyde had undergone a purely thermal decomposition during the experiment.

2nd Experiment.

Pressure of aldehyde vapour introduced = 2'33 mm. 9 , 7 9 oxygen (dry) 9 , = 233 ,,

526 19

The mixture was ciroulated for 24 hours; at first, a rapid fall of pressure was observed, followed by a slow and continuous rise. The final pressure of the dry produets was 450 mm.

The liquid in the worm again contained much formaldehyde, and the gaseous products had nearly the same composition as those obtained in the first experiment, namely :

Pcr cent. Per cent. Carbon dioxide ......... 24.6 Methane ......... 19.0 Carbon monoxide.. .... 5 1 *4 Hydrogen ........ 4-1 Nitrogen ................ 0.9

39.5 ~Yxpriirzmt.

In this experiment, pressure records were taken every 15 minutes, and the furnace was turned out as soon as the pressure fall had ceased.

Pressure of aldehyde vapour introduced = 283 mm. 7 9 9 , oxygen (dry) Y, = 265 ), -

548 ,, The records were as follows :

Tcmpcrature of Corrected pressure Time in combustion tube of ary minutes. T O . mixture,

0 ................. 479O .................. 548 mm. 15 .................. 479 .................. 513 ,, 30 .................. 479 .................. 496 ,, 45 .................. 479 .................. 490 ), 60 .................. 479 .................. 490 ,,

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THE SLOW COMBUSTION OF ETHANE. 727

The liquid in the worm again contained formaldehyde, and the gaseous products, which contained no free oxygen, had the follo.cving composition :

Per cent. Per cent. Carbon dioxide.. ....... 34.35 Methane.. ....... 15.35

Nitrogen.. ............... 1 -05 Carbon monoxide.. . . . 48.25 Hydrogen ....... 1.00

The indications obtained in the above experiments of the thermal decomposition of acetaldehyde vapour in contact with the heated surface led us to try tthe effect of circulating acetaldehyde vapour itself in our apparatus, W e have already stated (p. 695) tha t acetaldehyde, when heated in borosilicate bulbs a t 300-350°, under- goes simple decomposition in accordance with the equation CH;CHO = CH, + CO. The changes which occur when the aldehyde vapour is passed over a surface of porous porcelain maintained a t 450" are, however, of a more complex character. Some polymerisation or condensation takes place, and the condensed molecules undergo thermal decomposition as well as those of the simpler acetaldehyde vapour. The gaseous pro- ducts from one experiment, for instance, contained : CO, = 55.5 ; CO = 6.7 ; C,H,- 0.7 ; CH, = 31.0 ; and H, = 3.1 per cent.

When, however, the aldehyde vapour mas largely diluted with inert nitrogen, relatively much larger proportions of methane were formed, The whole subject of the thermal decomposition of these aldehyde vapours, which requires careful working out in detail, is now being taken in hand.

Experiments are also beiDg carried out in these laboratories on (1) the slow combustion of acetylene and ethylene, (2) the action of ozone on the simpler hydrocarbons at the ordinary temperature, and (3) the union of hydrogen and oxygen, and of carbon monoxide and oxygen, in contact with heated surfaces of porous porcelain.

I n conclusion, we desire to tender our best thanks to the Govern- ment Grant Committee of the Royal Society for repeated grants towards the expenses of this and allied researches.

TITS OWENS COLLEGIG, MANCIIESTER.

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