244 : Ma*. Cavendish’s Account of form 
6i the fame acid, diluted with a quarter of its weight of water*. 
44 fuppofing the acid and fnow to be both at 2& Q of heat; and 
“ there is no reafon to think, that the event will be different iif 
44 they are colder; for the undiluted acid will not begin to 
44 generate cold, until fo much fnow is dilTolved as to increafe 
44 its heat from 28° to 51 0 , fo that no greater cold will be 
44 produced, than would be obtained by mixing the diluted acid 
44 heated to 51° with fnow of the heat of 28°. This method 
44 of adding fnow gradually to an acid, is much the belt way 
44 I know of finding what flrength it ought to be of, in order 
44 to produce the greatefl effect poffible.” 
As it feemed likely that, by following this method, a greater 
degree of cold might be produced than had been done hitherto* , 
1 Tent three other bottles of fpirit of nitre and oil of vitriol, all 
three diluted, but not fo much fo, but that I thought they 
would require a little further dilution, in order to reduce them 
to their propereft degree of flrength. I alfi> fent a bottle of 
highly reflified fpirit of wine, and a mixture of equal quanti- 
ties of the above-mentioned common fpirit of nitre and oil of 
vitriol; and defired Mr. M c Nab to find what degree of cold 
could be produced by mixing them with fnow, after having 
firfl reduced them, in the above-mentioned manner^ to their befk 
degree of flrength 
He was alfo defired to afcertain how much fnow he added ;- 
for as their flrength was determined before they were fent out*, 
it would thereby be known what was the befl flrength of thefe 
liquors for frigorific mixtures# 
* This might have been done at home; but I thought it not unlikely that the 
ftrength found this way might differ, in fome meafure, according to the heat in 
which the experiment was tried. 
All 
