o n Mr, 
n ut Chios’s Experiments, 
3 : 2 5 
mateiials was + 26°, I have lunk the thermometer to - 29 0 ; fo 
that an 'addition ot 55 0 of cold was produced. 
It is remai table, that 111 none of Mr. Hutchins's experi- 
ments the cold ot the mixture was more than 6° of the lpirit 
thermometer below the point of freezing quickiilver, which is 
fo little that it might incline one to think, that the fpirit of 
nitre ufed by him was weak. This, however, was not the cafe, 
as its fpecific gravity at 58° of heat was 1,4923. It was able to 
diflolve — - its weight of marble, and contained very little mix- 
ture ot the vitriolic or marine acid : as well as I could judge 
from what experience I have of fpirit of nitre, it was as little 
phlogiflicated as- acid of that ftrength ufually is. 
But, however extraordinary it may at firft appear, there is 
the utmoffc reafon to think, that a rather greater degree of cold 
would have been obtained if the fpirit of nitre had been 
weaker; for I found, by adding fnow gradually to fome of 
this acid, that the addition of a fmall quantity produced heat 
inftead of cold ; and it was not until fo much was added as to 
mcieafe the heat from 28° to that the addition of more 
fnow began to produce cold ; the quantity of fnow required 
for this purpofe being pretty exactly one-quarter of the weight 
ot the fpirit of nitre, and the heat of the fnow and air of the 
room, as well as of the acid, being 28°. The reafon of this 
is, that a great deal of heat is produced by mixing water with 
fpirit of nitre, and the ftronger the fpirit is, the greater is the 
heat produced. Now it appears from this experiment, that 
before the acid was diluted, the heat produced by its union with 
the water formed from the melted fnow was greater than the 
cold produced by the melting of the fnow ; and it was not till 
it was diluted by the addition of one-quarter of it$ weight of 
that-: 
