352 BIOT ON THE EMPLOYMENT OF POLARIZED LIGHT ~ 
pletely with this same liquid, the weight of which I measured. 
The latter, compared with the weight of the same volume of 
water, gave the density of the essence 0°87908; and the pre- 
ceding operations made known the density of the solid sugar in 
relation to it: this latter was found to be 1:807937. The pro- 
duct therefore of these two numbers gives the density of the 
candied sugar compared to distilled water, which is thus equal 
to 158933. This value differs very little from those of 8, 
given in the last column of our first table, as being determined 
from the four aqueous solutions there considered. From this 
therefore it is evident that the sugar-candy, on the point of 
separating from water in order to solidify with the portion of 
that liquid which enters into its crystallization, forms a system 
differmg very little in density from that which it becomes 
in the solid state. However, the comparison of this latter 
density with the value of 3, determined by calculation, is only 
admissible here on neglecting the slight inequalities by which 
the aqueous solutions of sugar-candy deviate from the law of 
simple mixture ; as also on leaving out of question the difference 
which existed between the temperatures of these solutions and 
that at which the density of the sugar in the crystallized state 
was determined experimentally. 
44. I have related in my memoirs several experiments on 
mixed systems, the proportions of which were determined by 
volumes, and which appear to me likewise to be formed with- 
out apparent contraction or dilatation. They were of such 
a nature that the liquids composing them might be supposed 
not to enter into a chemical combination with one another, at 
least in the ordinary sense. There were, for example, various 
essential oils mixed together, or with fatty oils rendered 
colourless by long exposure to light. The constancy of the cha- 
a(P+K) 
P/é 
state of simple mixture. I regret however that I did not then 
verify this presumption by the direct observation of the densities. 
But fortunately I am able to draw from my observations already 
published a much more decisive example than those could have 
been. 
We shall see presently that the solutions of tartaric acid in 
water deviate constantly, and in all proportions, from the law of 
a simple mixture. Having formed such a solution, in accu- 
racteristic function always accompanied this presumed 
