C 270 3 
XIII. Observations on the best Methods of producing artificial 
Cold. By Mr. Richard Walker. Communicated by Martin 
Wall, M. D. F. R. S, 
Read May 14, 1795. 
Having already investigated the means of producing artifi- 
cial cold, and at the conclusion of my last paper (on the con- 
gelation of quicksilver) dismissed that part of the subject, the 
best method of making use of those means naturally becomes 
a desideratum ; to that therefore I have lately given my at- 
tention, and flatter myself that the following observations may 
be considered as an useful appendix to my former papers. The 
freezing point of quicksilver being now as determined a point 
on the scale of a thermometer, viz. — 39 0 , as the freezing point 
of water ; and as this metal, exhibited in its solid state, affords 
an interesting as well as curious phamomenon ; I shall apply 
what I have to say principally to that object. 
Frequent occasions having occurred to me of observing the 
superiority of snow, in experiments of this kind, to salts, even 
in their fittest state, that is, fresh crystallized, and reduced to 
very fine powder, I resolved upon adopting a kind of artificial 
snow. 
The first method which naturally presented itself, was by 
condensing steam into hoar-frost ; this answered the purpose, 
as might be expected, exceedingly well ; but the difficulty and 
