2^6 Mr. Keir’s Experiments on 
1 thought of afcertaining their fpecific gravity by adding gra- 
dually to this fluid part fome concentrated vitriolic acid, till 
the crystals Should float in the liquor, the examination of 
whole fpecific gravity would determine that of the floating cry- 
stals. But 1 was furprifed to And, that the cryltals funk even 
in the concentrated acid, and confequently were denfer. I 
then poured fome of the congelable acid, previoufly brought 
to the freezing temperature, into a graduated narrow cylin- 
drical glafs, up to a certain mark, which indicated a lpace 
equal to that occupied by 200 grains of water. The glafs was 
placed in a mixture of fnow, fait, and water, and when the 
acid was frozen, a mark was made 011 the part of the glafs to* 
which the acid had funk. Having thawed the acid, and 
emptied the glafs, 1 filled it with water to the mark to which 
the acid had funk by freezing, and I found, that fifteen grains 
more of water were required to raife it to the mark exprefling 
200 grains ; which fhews, that the diminution of bulk, luf- 
tained by the acid in freezing, had been equal to ~ of the 
• y 1 3 * 3 
whole. 
Computing from this datum , we Ihould eflimate the fpecific 
gravity of the congealed acid to have been 1924; but as it 
contained evidently a great number of bubbles, its real fpecific 
gravity mtlft be considerably greater than the above determina- 
tion, and cannot eafily be afcertained on account of thefe bub- 
bles. By way of companion, I obferved the alteration of 
bulk which water contained in the fame cylindrical glafs would 
fuffer by freezing ; and I found that its expansion was equal to 
about T J -th part of its bulk. The water had been previoufly 
boiled ; but it neverthelefs contained numberlefs bubbles. In 
this refpe6f then there is a remarkable difference between the 
congelations of water and of vitriolic .acid ; but, perhaps, the 
difference 
