380 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 20, No. 4

TIME not quite so apparent in Figure 4 as they are in Figure 2.

Effect of Temperature on Germicidal Action of Alkali Minutes

1 perature-48.8" C. An experiment was now run in which 2

3 the concentration of the sodium hydroxide was kept a t 0.5 4 5

Thus far the experiments have dealt with but one tem-

per cent and four temperatures were used-37.7, 43.3, 48.8,

wash water from forty bottles was used, which was plated in the manner already described. The concentrations of the alkali were higher in the second experiment than in the first. (Table 11)

Figure 3 is a graphical presentation of this data in which it will be seen there is a close parallel to the experiments with sodium hydroxide, although the germicidal action was less. The 0.5 per cent solution of pH 11 was only slightly germicidal; that of 0.7 per cent was but very little better. The concentrations of 1.0 and 2.0 per cent were quite efficient, although to get sterility the 2.0 per cent solution was needed

TEMPERATURE

37 7 ° C . 43.3'C. 48.8OC. 54.4'C.

4000 1500 500 200 2000 750 400 150 1500 500 300 50 1000 300 100 40 750 200 60 10

for periods of 3 to 5 minu tes . The pH va lue of t hese two solutions was 11.4 and 11.6, respec t ive ly . T h e germicidal effi- ciency was about 85 per cent for the 0.5 per cent solution, 95 per cent for the 0.7 per cent, and better than

of 0.5 Per Cent of NaOH and T i m e as and 2.0 per Cent SOlU- Measured by Bacteria Surviving tions. It is thus seen that the less alkaline solutions are not so efficient as the so-

0

Tme in minutes Figure 5-Relation between Temperature 99 per cent for the

a n d 54.4' C. The p rocedure was the s a m e a s ou t l ined above in every other respect. The results are given in Table I11 and in Figures 5 and 6. The relation be-

$ 8 tween t e m p e r a t u r e / / F \ and time is brought

lethal" lines are again 1 / I / ,

/T- 7- 7- s ? out here. The "iso-

in ev idence in Fig- mJj!-~/id,&4<4 I

/ I / 1 / I ' I /

1 ~/ ure 6.

Although these ex- periments have been , / I ,

I a 5 544

/ 50

reported as averages ~& I /

of a number of deter- 37? Temperature 43 3 ,n degd$*cent minations. this is fre- ~ Temperature mcrev3es -

ure 6-"Isolethal" Effect of Action of

practice. On inspect- ing the individual determinations it was seen, however, that there was a close agreement in the action of alkalies. By averaging them the minor differences that were found were eliminated.

Fumigation of Stored-Product Insects with Certain Alkyl and Alkylene Formates'

R. T. Cotton and R. C. Roark BUREAU O F ENTOMOLOGY AND BUREAU OF CHEMISTRY AND SOILS, WASHINGTON, D. c.

N A previous paper2 the authors announced their in- tention of publishing preliminary accounts of promising fumigants whenever they should be discovered during

the course of a systematic examination of aliphatic compounds without waiting for the completion of the entire investigation. In the present paper attention is called to certain alkyl and alkylene esters of formic acid.

Historical

I

The insecticidal action of methyl, ethyl, and isopropyl formates against rice weevils, flour weevils, and granary weevils in bell jars was first tested in 1923 by the writers and their ass~c ia tes ,~ but the exact minimum dose was not determined accurately. Certain mixtures of formates with other compounds were also tested-for example, methyl formate with ethyl bromide, ethyl formate with ethyl bro- mide, ethyl formate with ethylene bromide, and ethyl for-

1 Presented before the Division of Agricultural and Food Chemistry at the 74th Meeting of the American Chemical Society, Detroit, Mich., September 6 to 10, 1927.

3 J . Econ. EnfomoZ., 20, 636 (1927). 8 U. S. Dept. Agr., Depl. Bull. 1313 (1925).

mate with carbon tetrachloride. A mixture of equal parts by weight of ethyl formate and carbon tetrachloride killed 100 per cent of the weevils in a box car of wheat when applied a t the rate of 10 pounds per 1000 cubic feet of enclosed space. The mean temperature was 74" F. and 24 hours' exposure was allowed.

Following the publication of the results of these tests, the I. G. Farbenindustrie of Germany applied for patents in certain foreign countries covering the use of the esters (specifically the methyl and ethyl esters) of formic acid for the destruction of insects attacking cereals. In the specifications of these patents4 it is stated that the vapor of methyl formate a t a concentration of 1 to 10,000 kills grain weevils in 30 minutes. (A concentration of 0.01 per cent by volume of methyl formate vapor is equivalent to 0.27 mg. per liter.)

Recently Tattersfields has shown that methyl formate is quite toxic to aphids (A . rumicis) when sprayed upon

4 French Patent 617.784 (February 25, 1927; appl. June 18, 1926); Austrian Patent 106,725 (June 25, 1927; appl. June 17, 1926; appl. i n Germany, January 19,1926).

8 J . Agr. Sci , 17, 181 (1927).

April, 1928 INDUSTRIAL AND ENGINEERING CHEMISTRY 381

them in dilute aqueous solution. Since the publication in 1925 of the results of the writers' early tests with formates, ethyl formate has come into large-scale use in this country for the fumigation of certain food products.

Tests to determine the fire hazard of fumigants have recently been made in this laboratory, the results of which will be published shortly, but on account of their high vapor pressures a t 122" F. it is not possible to make methyl or ethyl formate free from fire hazard a t this temperature by admixture with carbon tetrachloride unless such an excess of the non-burnable diluent is used that the mixture contains less than 10 per cent by weight of the formate. The toxicities of such mixtures to insects are only slightly greater than that of carbon tetrachloride alone.

In view of the high toxicity shown by the formates pre- viously tested, it seemed worth while to test additional members of this group of compounds with the purpose of discovering some that could be utilized in admixture with carbon tetrachloride in such proportions as to be free from fire hazard and yet retain the toxic value of the formate.

Experimental

An initial series of tests with the formates as fumigants was made in half-liter glass flasks against the rice weevil (Sitophilus orym L.). The weevils were placed in cotton- plugged vials, ten to each vial, together with some cracked corn. One or two vials were placed in each 500-cc. Erlen- meyer flask, and covered with 250 cc. (approximately 200 grams) of wheat. The calculated quantity of fumigant was allowed to drop upon the grain from a pipet graduated to 0.01 cc. The flasks were then tightly stoppered and al- lowed to stand 24 hours a t the temperature of the laboratory (21" to 27" C.), a t the end of which time the weevils were removed and the percentage mortality determined.

According to this method of testing, the minimum lethal dose includes the quantity of material, in the form of vapor, just sufficient to kill all the weevils plus the quantity ab- sorbed by the wheat. In the absence of wheat and with complete vaporization and thorough mixing of the vapor of the fumigant with the air in the flask, the figures for the minimum lethal dose would be smaller. However, this method of testing in the presence of a relatively large mass of grain simulates conditions met in large-scale fumigation of box cars, bins, etc.

Table I shows the results. The minimum lethal dose for each compound is the approximate figure as determined by from five to thirty separate tests.

Table I-Minimum Lethal Dose of Alkyl a n d Alkylene Formates tb-Rice Weevils Covered with Wheat during 24 Hours' Exposure

a t Room Temperature FORMATE BOILIXG POINT MINIMUM LETHAL DOSE

c. Mg. p e r Mer Methyl 3 1 . 5 t o 3 2 . 5

n-Pronvl 7 8 . 5 t o 8 1 . 5 Ethyl 5 3 . 5 t o 55

Isopropyl 63 to 64 %-Butyl 105 to 106 sec-Butvl 94 to 97 Isobutil 96 to 97 Isoamyl 122 to 123 Allyl 82 to 84

39 72 72 53

109 2 5 _. 35 70 38

Cost of Formates

The usual method of making esters of formic acid is to combine formic acid with the appropriate alcohol in the presence of a dehydrating agent, such as calcium chloride. Formic acid of 90 per cent strength can be purchased for about 11 cents per pound, and the alcohols range in price from a few cents for the common ones to $1.00 per pound for n-propyl and isobutyl alcohols. Alkyl formates are not a t present commercially obtainable, but correspondence with manufacturers discloses that if a commercial demand

for the formates develops, methyl, ethyl, n-butyl, isopropyl, and isoamyl formates can probably be sold for not more than 35 to 50 cents per pound each; and n-propyl, sec-butyl, and isobutyl formates should not cost more than $1.00 per pound each. Allyl formate will doubtless continue high, owing to the high cost of allyl alcohol.

Inflammability

The vapor pres- sures of the methyl and ethyl esters of formic acid are so high a t ordinary temperatures that mixing carbon tetra- chloride with them does not entirely remove their fire hazard. The higher members of the series can be rendered free from fire hazard by the addition of carbon tetrachloride in the proportions shown in Table 11. (By "free from fire hazard" is understood a material the vapor of which heated to 122" F. in admixture with air in a box will not propagate a flame when sparked.)

All the alkyl formates are inflammable.

Table 11-Pro erties of Non-Inflammable Mixtures of Carbon fetrachloride with Alkyl Formates

SP. GR. OF WEIGHT OF MIXTURE 1 GALLON OP

FORMATE IN MIXTURE (20°/4' C.) MIXTURE ALKYL FORMATE By volume By weight (CALCD ) (CALCD 1

Per cent Per cent Pounds n-Propyl 30 19 5 1 387 11 6 Isopropyl 25 15 6 1.417 11 8 n - B u t y 1 40 27 6 1 321 11 0 sec-Butyl 40 26 9 1 310 10 9 Isobutyl 40 26 8 1 310 10 8 Isoamyl 40 26 7 1 305 10 9

Effect of Alkyl Formates on Various Commodities

The alkyl formates, both alone and in admixture with carbon tetrachloride, are good solvents for oils, grease, varnish, lacquers, and various organic materials. The liquid formates should not be poured on varnished or lac- quered furniture or the like. However, these fumigants have no bleaching or staining action.

In contact with water or water vapor alkyl formates may be hydrolyzed into formic acid and an alcohol. No bad effects may be feared from the alcohols resulting from a decomposition of this kind, but formic acid may exert a strong corroding effect on an unprotected metallic surface.

The effects upon man of consuming food products con- taining alkyl formates or formic acid have not been deter- mined. It is not believed that the corrosive effect or the residual toxic effect of the alkyl formates in fumigated food- stuffs will be serious, but users of this class of fumigants are warned that in these respects the alkyl formates are in the experimental stage only.

Effect of Vapors of Alkyl and Alkylene Formates on Germination of Wheat

Table I11 gives the results of germination tests upon wheat before and after fumigation with some of the esters of formic acid. These tests were made in duplicate upon one hundred kernels of wheat.

Table 111-Effect of Vapors of Alkyl a n d Alkylene Formates upon Germination of Wheat

MINIMUM DOSE Actual Comparative FORMATE LETHAL DOSE" APPLIED overcheck (check = 100)

GERMINATION

(Grams per kg wheat) Methyl Ethyl n-Propyl Isopropyl n-Butyl n-Butyl sec-Butyl sa-Butyl Isobutyl Isoamyl

0 . 1 0.18 0.1s 0 . 1 3 0 . 2 7 0 . 2 7 0 .09 0 .09 0 .09 0 . 1 8

0 . 2 0 . 2 0 . 2 0 . 2 0 . 2 0 . 7 0 . 2 1 . 1 0 . 2 0 . 2

91/86 .5 90 .5 /86 .5 9 l / S 6 . 5 92.5/86.5 91/86 .5 78.5/79 95/97 .5 88/97 ,5 87.5/86,5 9 1 . 5 / 8 6 . 5

105 105 105 107 105 100 97 90

101 106

Allyl 0 . 1 0 . 2 91 .5)97 .5 94 Allyl 0 . 1 1 . 2 85/97.5 87 a This is the minimum lethal dose under the conditions of the test-

namely, 200 grams of wheat in a 500-cc. Erlenmeyer Bask, expressed as grams fumigant per kilogram of wheat instead of milligrams per liter of space.

382 INDUSTRIAL AND ENGINEERI,VG CHEMISTRY T’ol. 20. No. 4

It is evident that none of the formates tested, in dosages greater than those necessary to kill all weevils, had an adverse effect upon the germination of wheat.

Table IV-Fumigation Tests i n a 500-Cubic Foot Vault wi th Mixtures of Alkyl Formate and Carbon Tetrachloridea

(Length of exposure, 24 hours) LARVAE KLLLED

An- Tineola Atta- FUMIGANT MIXTURE threnus biselli- genus

Formate CClr DOSAGE T E M P . vorax ella piceus Lbs. per M .

Volumes Volumes cu. f t . F. Per cent Per cent Per cent 3 (n-propyl)

1 (isopropyl)

2 (sec-butyl)

2 (isobutyl)

2 (isoamyl)

10 I I b 13 14 7 8 8 9 7

76 100 60 100 92 100 96 100 100

8.5 100 100 100 90 100 100 100 100

70 100 86 100 86 100 90 100 100

a In all tests 20 specimens of clothes moths and 50 specimens of each of

b Italic figures indicate dosage for perfect kill. other species were used.

Large-Scale Tests

Tests with these alkyl formates which can be made free from fire hazard by admixture with carbon tetrachloride were conducted on a larger scale in a commercial-type fumi- gation vault of 500 cubic feet capacity. The fumigant was

poured through a trap door in the top of the vault into a shallow pan or trough suspended near the ceiling. The vault was then closed tightly for 24 hours. The insects used in the tests were the larvae of the clothes moth, Tineola biselliella, the black carpet beetle, Attagenus piceus, and the furniture beetle, Anthrenus voraz, species all highly resistant to fumigation. The larvae were placed in cotton-stoppered vials and buried in pieces of overstuffed furniture. Table IV shows the results of these tests.

Additional tests indicate that the effectiveness of this group of fumigants decreases with the decrease in tem- perature and that to obtain perfect results the temperature should be at least 75’ F.

Summary

The vapors of methyl, ethyl, n-propyl, isopropyl, n- butyl, sec-butyl, isobutyl, isoamyl, and allyl formates are toxic to insects infesting stored products, such as rice weevils, clothes moths, carpet beetles, and furniture beetles.

All these formates, except the methyl and ethyl formates, can be made free from fire hazard by the addition of carbon tetrachloride to the extent of 60 to 75 per cent by volume of the mixture, and some of these mixtures appear promising as economical fumigants for use in fumigating vaults.

A Simplified Manometer for Vacuum Distillations’ G. B. Heisig

SCHOOL OF CHEMISTRY, UNIVERSITY OF MINNESOTA, h1INNEAPOLIS. MI“.

NYOKE who has run vacuum distillations using the regulation “S” type of manometer knows what a A tedious job it is to clean and refill it if by chance his

distillate has contaminated the mercury in the manometer. To minimize this difficulty the writer uses a somewhat dif- ferent type of manometer whose construction is apparent from the accompanying sketch. It is made of Pyrex glass tubing.

To fill the manometer, a layer of mercury about 7 mm. deep is poured into the reservoir. The manometer is then con- nected to the suction line and the vacuum is broken when the pressure reaches a minimum. This can be determined by the noise of the water pump. As the pressure increases the mercury will rise nearly to the top of the column. The manometer is then inverted and again attached to the pump. When the pressure has been reduced, the column of mercury is heated until the mercury boils. At the same time the tube should be tapped with a stick to help the air bubbles to rise. When the air has been boiled out, the heating is stopped, the manometer is placed in its usual position, and the pump is disconnected. The cleaning of the apparatus with cleaning mixture, the drying with alcohol and then ether, and the filling and boiling of the mercury require about an hour. When filled, the manometer is mounted on a wooden stand.

Besides being easy to fill, the manometer has other ad- vantages. Owing to the capillary constriction there is no danger of the mercury striking the top of the tube with suffi- cient force to break it. Even when a system is a t a pressure of 2 or 3 mm. the mercury rises gently to the top of the tube when the vacuum is broken.

The reading of the column is facilitated by the fact that it is read directly, not by the difference of the height of mer- cury in two columns as in the “5” type of manometer. A millimeter scale made from a celluloid ruler or coordinate

1 Received February 6, 1928.

paper is attached beside the column of mercury, and is ad- justed by comparing the manometer a t different pressures with a standard manometer. If a standard manometer is not available, nearly as accurate results may be obtained by putting the zero of the scale on a level with the surface of

li I I I

A Simplified Manometer

the mercury in the reservoir. Since the mercury from the tube spreads over the large pool as the pressure decreases, the height of the mercury in the pool increases only about 0.5 mm. even when the entire tube is emptied into it. The maximum error in reading, which would take place a t very low pressures, would be 0.5 mm. For ordinary vacuum