266 Mr. Cavendishes Account of fame 
by placing the jar in which it was contained in a freezing mix- 
ture of oil of vitriol and fnow ; the fnow intended to be ufed 
was alfo cooled by placing it under the veffel in which the 
freezing mixture was made. As foon as the acid in the jar 
was cooled to the temperature of — 57°!, a little of the fnow 
was added, on which it immediately began to freeze* and rofe 
to — 36° ; but in about 40 minutes, as the jar was ftill kept in the 
freezing mixture, it funk to -48°; by which time it was 
grown very thick and gritty, efpecially at bottom. More of 
the cooled fnow was then added, which in a fhort time made 
it fink to — 78°!, and at the fame time the thicknefs and tena*- 
city of the mixture diminifhed ; fo that by the time it arrived 
at the greatefl: degree of cold, very little thicknefs remained; 
It is worth inquiring, what was the reafon of the greater 
degree of cold produced in this than in the preceding experi- 
ment ? It could not.be owing to the materials being colder £ 
for at the time of the fecond addition of fnow, at which time the 
experiment may be confidered to have begun, the acid was not 
colder than at the beginning of the preceding experiment, and 
the fnow in all probability not much colder. It could not bo 
owing neither to the jar having been kept in the freezing mix- 
ture : for though that mixture was three or four degrees colder 
than the air in the preceding experiment, yet the acid in the jar* 
before it acquired much addition of cold, would be robbed of its 
cold fafter by the mixture than it would by air cf the fame 
temperature as that in the preceding experiment. Neither could 
it proceed from any difference in the ftrength of the acid ^ for 
what difference there was muft have done more hurt than good* 
The true reafon is, that the acid was in a date of congelation 
for as the congealed acid united to the fnow and became fluid by 
the union, it is plain* that cold muft have been produced both 
by 
