IN STUDYING QUESTIONS OF CHEMICAL MECHANICS, 373 
weight between the water and acid. Now, the two terms of this 
relation include the coefficient (A), which varies with the tem- 
perature, whilst (B) does not vary sensibly, at least in the inter- 
val of temperatures which my experiments have comprised. It 
is therefore evident that the relation itself changes in value 
when the temperature changes, so that the maximum of rotatory 
power of the groups corresponds to proportions always varying 
of the two combined principles. Nevertheless, the form of the 
parabola remains invariable for the same luminous ray, at every 
temperature, since its parameter depends only on (B). The in- 
fluence of the intervention of water on the maximum of mole- 
cular power is readily perceived in the expression of the relation 
of the ponderable elements to which this maximum answers. It 
is only necessary for this purpose to give it the following form :— 
(B)—(A)_,___2(A) 
(B) + (A) (B) + (A)’ 
Let us admit the constancy of (B) at all temperatures, as well as 
the variability of (A) as found by our experiments. Towards 
23° C. (A) becomes null, and the maximum power of the mole- 
cular groups takes place for equal weights of water and acid. 
Above 23°, (A) being positive, the fraction annexed to the unit 
becomes negative: there is then less water than acid needed ; 
and if A increased indefinitely, the maximum would correspond 
to an amount of water Jess in proportion as the temperature 
increases. As the ponderable relation of the two elements 
must be positive from the nature of the physical question, it 
would reach its least value, which is null, if (A) could become 
equal to (B), in which case no water should be added to the 
acid ; and at still higher temperatures, every addition of water 
would weaken the action. Below 23°, (A) becoming negative, 
the circumstances would be reversed; the maximum of power 
would answer to a greater proportion of water than acid, and 
to an amount proportionately greater as (A) increases in this 
direction. Lastly, if its negative value could become equal to 
the constant and positive value of (B), the maximum power 
would only be obtained by the employment of an infinite por- 
tion of water. 
60. I have thought it useful to develope these details, because 
by pointing out all the variations of the general action which 
the tartaric solutions exercise on polarized light, and deriving 
