778

LXXVII1.-The Cornpowads of Ethyl Alcohol with Water.

By D. MENDEL~EFF.

DALTON'S great doctrine respecting the atomic constitution of matter has not hitherto been applied to the explanation of the phenomena of dissolntion, and notwithstanding the many admirable investigations on this subject, the views of chemists respecting the relation between ordinary cases of combination and the phenomena of dissolution remain still undefined. However, the part played by solutions in nature, i n the laboratory, and in the arts, is so important that the fulness of our chemical conceptions seems to suffer from the want of clearness in the doctrine relating to them.

In communicating the result of some of my investigations and hypotheses, I will restrict myself to the particular case of solutions of ethylic alcohol in water, chiefly because, among solutions, the mix- tures of alcohol and water have been most fully studied, at any rate, with reference to the dependence of change of specific gravity on the proportion of alcohol. Practical necessity has led to many accurate investigations of this subject, and from the time of Gilpin to our own the mass of accurate information has been steadily increasing, and permits of a sound judgment being formed. Collating all the infor- mation a t our disposal, I have constructed the following Table [I) of the most trustworthy data :-

TABLE I.

Percentage by weight of

alcohol, 21.

5 10 15 20 25 30 35 40 45 50

Specific gravity in a vacuum a t 15" C., taking water a t 4' = 10,000, and a t 15' = 9991'6,

8 .

9904 '1 9831.2 9768 *4 9707.9 9644'3 9570.2 9484.5 9389.6 9287 ' 8 9179.0

Percentage by weight of

alcohol, P*

55 60 65 70 75 80

90 95

100

a5

Specific p a r i t y in a vacuum at 15' C., taking water a t 4" = 10,000, and at

15" = 9991.6, 8 .

9067.4 8953.8 8838.6 8719.5 8601.4 8479.8 8354.8 8225 '0 8086.9 7936.6

It is interesting to note that, after making some necessary correc-

THE COMPOUNDS OF ETHYL ALCOHOL WITH WATER. 779

tions, the data mentioned by different observers, taking only the most trustworthy observations, show very small differences. For example, in the case of a solution of 50 per cent. of alcohol we find the fol- lowing :-

TABLE 11.

Gilpin.. ................ Gay-Lnssac ............. Fownes ................. Drinkwater. ............. Baumhauer ............. Mendeleeff.. ............ Dupr6 and Page ......... Squibb., ................

1792 1824 1847 1848 1060 1865 1869 1884

9187.0 9182 .0 9180.0 9178.8 9180 .0 9179.7 9178.5 9178 .O

~

In the above table of specific gravities, the greatest error is within 0.0002, and only in some cases attains 0.0003. No other solution besides that of alcohol, and none of its other properties, are known with such a degree of accuracy, and in addition the solutions can be obtained in all proportions, and therefore the example which I have taken is a typical one.

Without describing the methods by which I have arrived a t my views on the nature of solutions (some of the preliminary investi- gations on this subject have been published by me in the Journal of the Russian Chemical Society, and in Professor Ostwald’s Zeitschrift j i j rphys ikaZishe Chemie) , I will now state the hypothesis which is in accordance with them.

Solutions may be regarded as strictly definite, atomic chemical combinations a t temperatures higher than their dissociation tem- perature. Definite chemical substances may be either formed or decomposed a t temperatures which are higher than those a t which dissociation commences ; the same phenomenon occurs in solutions j at ordinary temperatures they can be either formed o r decomposed. In addition, the equilibrium between the quantity of the definite compound and of its products of dissociation is defined by the laws of chemical equilibrium, which laws require a relation between equal volumes and their dependence on the mass of the active component parts. Therefore, i f the above hypothesis of solution be correct, com- parisons must be made of equal volumes ; the specific gravities are the weights of equal volumes, and moreover we must expect the specific gravities of solutions to depend on the extent to which the active substances are produced ; therefore, the expression for specific gravity s, as a function of the percentage composition p , must be a parabola of the second order :-

s = N ( p n)(100 - p I a), 3 H 3

780 MENDELEEFF : THE COMPOUNDS OF

or t,his may be represented by the general equation-

s = C + Ap + Bp2. Between two definite compounds which exist in solutions, we must

expect that the differential coefficient - will be a rectilinear function dS

4J o f p :

This consequence can, in the first place, be verified by experiment, and secondly gives the means of ascertaining what are the definite combinations existing in the solution.

Applying this method to the solution of H1O and C2H60, three definite combinations are found to exist, namely-

C,H,O + 12H20 = 17.56 per cent. alcohol. CzH60 -+ 3H30 = 46.00 ,, $ 9

3CZH60 + HZO = 88.46 ,, 9 ,

dS The rectilinear character of the differential coefficient - is demon- dP

strated by the annexed diagram :-

- 10

- 20

- 30

- 20

- 30

The parabolas expressing the specific gravities a t 15" C. are calcu- lated by the formula-

I. s = 9991.6 - 17.9913 + 0,19581, 2 (9,36,1 9991.6 11. s = 9868.4 - 4 .0975~ - 0'1958p22(9265,6

- 0 .0443~ .8267.4 ' 111. S = 10166.6 - 17 .545~ IV. s = 9074.9 + 8'192p - 0.1958p2{7936.1

TVith change of temperature, the constants of the parabola change,

ETHYL ALCOHOL WITH WATER. 781

but for temperatures between -30" and +40", a t which accurate observations exist, the applicability of the parabolic expression is as exact as it is at 15", and for that temperature an example is given in line 111, which is the longest traced. The difference between the calculated and the observed results in no case exceeds the allowable errors of experiment, as the following table shows :-

TABLE 111.

Percentage of

alcohol.

50 55 60 65 70 75

85 80

Value by experiment.

Specific gravity.

9179 '0 9067'4 8953 'a 8838.6 8719.5 8601 '4

836 1. .8 a479 ' 8

Value by calculation.

Specific gravity.

9178.4 9067.3 8954.1 8838.6 8721 .O 8601 *1 8479 .o 8354.7

The hypothesis respecting the rectilinear character of the differen-

tial coefficient - has been proved to be correct, not only for solutions

of a hundred different salts, but also for solutioiis of H,SO,, of NH,, of HCl, and otber similar substances, and up to this time I have not met with a single solution which is an exception.

As the principle of my hypothesis lies in the idea of dissociation of definite compounds which exist in solutions, I intend to investigate minutely solutions at low temperatures, and I expect to obtain definite compounds in the solid state, and to explain the relation of the solid compounds which were obtained by me in 1868, and after- wards by Guthrie, who called them cryohydrates; indeed I have already made some experiments in that direction with the assistance of Mr. Teeshenko. Thus we have obtained the definite compound C,H,O + 12H,O in the solid state at -17" C., and the definite com- pound C,H,O + 3H,O in the crystalline form, a t a temperature which is attained by the mixture of solid carbonic anhydride and ether.

The fundamental propositions of my investigations, that is to say, firstly, the rectilinear character of the differential coefficient d 2. and, secondly, the existence in solutions of definite comhina-

d l 3 ' tions, I am developing in a special paper, in which I attempt, as far as possible, to distinguish clearly that portion of the theory which

ds dP

782 L I N G : ISOMERIC CHANGE I N THE

does not admit of question from the hypothesis which still requires verification and amplification.

I do not consider that my investigations are finally completed, and I only venture to lay them before a scientific society as footsteps along the road leading to the elucidation of the theory of dissolution in the light of Dalton’s teaching, and with the help of modern views respecting dissociation and the dynamic equilibrium of molecules, which I may be allowed to term ‘‘ association.”