the Congelation of Vitriolic Acid . 269 
have lately been made by Mr. M c Nab, at Hudfon’s Bay, on 
the congelation of acids by intenfe cold; an account of which 
experiments is given in the Philofophical Tran factions for 
1786, by Mr. Cavendish, at whole defire they had been 
made. Thefe experiments are the more valuable, as the den- 
sity of the acids employed, and the temperature, and other 
concomitant circumftances, have been diflinclly noted; and 
they are rendered Bill more interefting, by the very judicious 
remarks made on them by Mr. Cavendish. It is there re- 
lated, that a vitriolic acid, whofe fpecific gravity was to that 
of water as 1843.7 to 1000, froze when expofed to a cold of 
- 1 5 0 of Fahrenheit’s fcale ; that another more dilute vitri- 
olic acid, confifting of 629 parts of the former concentrated acid, 
and 351 parts of water, congealed in a temperature of —36°; 
and that when the acid was further diluted, it was found 
capable of fufiaining a much greater cold without freezing. 
In thefe experiments, as alio in thole of M. de Morveau, it 
appeared, that the whole of the acid did not congeal, but that 
part of it retained its fluidity. Mr. Cavendish found, on 
examining the part which had congealed, and that which had 
remained fluid, that they were nearly of the fame ftrength ; 
and he is thence led to think, that the difference between them, 
by which the one is more difpofed to congeal than the other, 
does not depend on their different ffrengths, but on fome qua- 
lity lefs obvious, and the fame which eonftitutes the difference 
between glacial and common oil of vitriol. In all the experi- 
ments which had been made by the Duke d’Ayen, M. de 
Morveau, and Mr. M c Nab, the vitriolic acid, when ftrong, 
had frozen with lefs cold than when diluted ; but thefe experi- 
ments did not enable Mr. Cavendish to determine, whether 
this acid has any determinate ftrength or point oj eafieft freezing 
Vol. LXXVII. R r (fuch 
