376 RELATIVE ATTRACTIONS OF 
change of weight: in this fluid state, it was again 
left as usual in the place of low temperature, and 
in a few hours it again became entirely crystal- 
lized. In this crystallized state it remained, when _ 
the experiment was discontinued, on the 10th of 
February. It, therefore, appears, that a temper- 
ature, ranging from 30° to 32°, or an evaporating 
force of from 0.24 to 0.26 of an inch of mercury, 
was sufficient to concentrate the acid so far as to 
give it a per centage of 67.8 real or anhydrous 
acid, and a sp. gr. about 1.7762; and that, while 
crystallized, it had no apparent further concen- 
tration given it by an evaporating force extending 
even to 0.32 of an inch of mercury. 
The acid under the unexhausted receiver con- 
tinued to lose weight till the 2nd of March; at 
which time the loss was found to be 6.3 grains: 
the residue in the dish contained 58.1 per cent. of 
anhydrous acid, and would have a sp. gr. about 
1.6405. The temperature just capable of effect- 
ing this degree of concentration was about 36°, 
equal an evaporating force of 0.30 inch of mer- 
cury. The atmospheric pressure under which 
the final concentration was effected, was from 
28.34 to 28.97 inches of mercury, as I find on 
reference to my general register. 
