yib Mr. cavendish’s Obfervatlons 
that fubflance, that the cold generated by the latter caufe be- 
gan to exceed the heat generated by the former. From what 
has been laid it is evident, that the cold of a freezing mixture, 
made with the undiluted acid, cannot be quite fo great as that 
of one made with the fame acid, diluted with a quarter of its 
weight of water, luppofmg the acid and fnow to be both at 
28° of heat, and there is no reafon to think, that the event 
will be different if thev are colder; for the Undiluted acid will 
isotherm to generate cold until fo much fnow is diflblved as to 
increafe its heat from 28° to 51 0 , fo that no greater cold will be 
produced than would be obtained by mixing the diluted acid 
heated to 51 0 with fnow of the heat of 28°. This method 
of adding fnow gradually to an acid is much the bed: way I 
know of finding what ftrength it ought to be of, in order to 
produce the greateft effect poffible. 
By means of this acid, diluted in the above-mentioned pro- 
portion, I froze the quickfilver in the thermometer called G by 
Mr. hutchins, on the 26th of laft February. I did not, in- 
deed, break the thermometer to examine the ftate of the quick- 
filver therein ; for as it funk to - 1 io° it muff certainly have 
been in part frozen ; but immediately took it out, and put the 
fpirit thermometer in its room, in order to find the cold of the 
mixture. It funk only to -30°; but, by making allowance 
for the fpirit in the tube being not fo cold as that in the ball, 
it appears, that if it had not been for this caufe i: would have 
funk to 35 0 *, which is 5 0 below the point of freezing, and 
is 
* As the furface of the freezing mixture anfwered to — 185'’ on the tube, there 
w ere 1 5 5 0 of fpirit in the tube which could hardly be cooled much below the 
temper of the air, and which mud, therefore, be warmer than that in the ball by 
about 55 0 of this thermometer, as the heat of the fpirit in the ball was before 
laid 
