264 Mr. Cavendish's Account of fome 
temperature of the acid rofe only one degree before it began to 
link, and the weight of the fnow added was only yJL of that 
of the acid, fo that its ftrength was reduced thereby to ,605 ; 
which is therefore the beft degree of ftrength for producing 
cold by the addition of fnow, when the degree of cold Jet out 
with is —3c 0 . This ftrength is one fifteenth part lefs than 
what I found myfelf, by a fimilar experiment, when .the tem- 
perature of the acid was +27 0 ; which fhews, that the beft 
degree of ftrength is rather lefs, when the degree of cold fet 
out with is great than when fmall, but that it does not differ 
much. 
23. The acid thus diluted was divided into two parts, and 
the next day Mr. M c Nab tried what degree of cold could be 
produced by adding fnow to one of them. The temperature 
of the air at the time was — 39% and the mixture funk by the 
procefs to — 55°|* The fnow diflolved readily, and the mix- 
ture did not lofe much of its fluidity until it had acquired 
nearly its greateft degree of cold, nor did any congealed mat- 
ter fink to the bottom in any part of the procefs. The quan- 
tity of fnow added was about of the weight of the acid, 
fo that the ftrength of the mixture was about ,325. 
24. On January i, thin cryftals of ice were found diffuled 
nil through this mixture, the temperature of the air being 
— 51°!, but that of the liquor was not tried. As this conge- 
lation muft have been of the aqueous kind, and feems to have 
taken place at the temperature of - 51°!, it Ihould follow, that 
this acid had no power of diflblving fnow in a cold of 5 1°| ; fo 
that it does not at firft appear why a cold four degrees greater 
than that Ihould have been produced in the foregoing experi- 
ment. The reafon is, that at the time the mixture arrived 
at - 55°i? it appeared by the diminution of its fluidity to have 
contained 
