IN STUDYING QUESTIONS OF CHEMICAL MECHANICS. 375 
exist, in proportions indefinitely varied, in the liquid state, form- 
ing chemical groups of variable constitution, according to the 
proportion of the elements of each system. We may even, in 
very general cases, discover by these means the numerical law 
according to which the constitution of the groups varies pro- 
gressively with these proportions. 
The existence and the character of these combinations are 
manifested immediately by the following experiment. If, to an 
aqueous solution of tartaric acid of a known quantity, a cold 
aqueous solution of boracic acid is added, in such proportions 
that the resulting system may exist in the liquid state, this sy- 
stem acts on polarized light quite otherwise than the primitive 
tartaric solution. Its specific action on one and the same simple 
ray is always more energetic; and it is exercised on luminous 
rays of various refrangibilities according to other laws of di- 
spersion. The difference is manifested as soon as boracic acid 
enters into the total system in a proportion less than 57255. 
With so feeble an amount, the law of dispersion peculiar to tar- 
taric acid has already disappeared; and, for proportions of 
boracic acid ever so little stronger, if not for that very amount, 
the mode of dispersion re-enters into the general law, in which 
the deviations experienced by the planes of polarization of the 
various simple rays are sensibly reciprocal to the squares of the 
lengths of their fits. 
62. To study these phenomena in their simplest phases, which 
hold out the expectation of discovering in them physical laws, 
I operated on systems such that the ponderable proportion of 
tartaric acid was always in a constant relation with the pro- 
portion of water, that of the boracic acid being the only variable 
element. It is therefore first necessary to state how such systems 
may be formed at pleasure. 
Let A’ and A” be two given aqueous solutions, the first of 
tartaric acid, the second of boracic acid, whose ponderable com- 
positions are known and expressed as follows :— 
Proportion of Proportion of | Numerical rela- 
3 : . acidin the unit | water in the tion of the two 
Designation of the solution. of weight of the junit of weight of} elements of 
solution. the solution. each solution. 
Tartaric solution A’ ......... / e +e =1 
Boracic solution A” ......... ry ef” “tev =)] 
It is required to compose with these two solutions a mixed 
