344 
Book I. 
NATURE OE 
In order to produce these effects, the salts employed 
must be fresh crystallized, and newly reduced to a very 
fine powder. The vessels in which the freezing mix 
ture is made should be very thin, and just large enough 
to hold it, and the materials should be mixed together 
as quickly as possible. The materials to be employed 
in order to produce great cold ought to be first reduced 
to the temperature marked in the Table, by placing 
them in some of the other freezing mixtures ; and then 
they are to be mixed together in a similar freezing mix 
ture. If, for instance, we wish to produce a cold 
46°, the snow and diluted nitric acid ought to be 
cooled down to o°, by putting the vessel which contains 
each of them into the 12th freezing mixture in the 
above Table, before they are mixed together. If a still 
greater cold is required, the materials to produce it are 
to be brought to the proper temperature by being pre 
viously placed in the second freezing mixture. This 
process is to be continued till the required degree of 
éold has been procured". 
SECT. IX. 
OF COMBUSTION. 
HaviNe examined the properties of caloric, and the 
changes which it produces on other bodies, it now only 
remains for us to consider the different methods by 
* Walker, Phil. Trans. 1795.