best Methods of producing artificial Cold. 283 
the utmost degree of cold this acid can produce with snow is 
— 46° ; which degree of cold may be produced by mixing the 
snow or ground ice and nitrous acid at o°. 
If it be required to make it perfectly solid and hard, a mix- 
ture of equal parts of the diluted vitriolic acid and nitrous 
acid should be used with the powdered ice, but then the ma- 
terials should not be less than — 1 o° before mixing. 
If a still greater could be required than a mixture of this 
kind can give, which is about — 56°, the diluted vitriolic acid 
alone should be used with snow or powdered ice, and the 
temperature at which the materials are to be mixed not less 
than — 20 0 . 
Select, according to the intention, either of the three fol- 
lowing mixtures : 
First, snow or pounded ice two parts, and common salt one 
part, which produces a cold of — f : 
Second, snow or pounded ice twelve parts, common salt five 
parts, and a pbwder, consisting of equal parts of common sal 
ammoniac and nitre mixed, five parts, which produces a cold 
of— 18 0 : 
Third, snow or pounded ice twelve parts, common salt five 
parts, and nitrous ammoniac in powder five parts, which pro- 
duces a cold of — 25 0 . 
The proportions which I have found to be the best for mix- 
ing the snow or powdered ice with the different acids, at dif- 
ferent temperatures, are these; viz. at -}- 30°, seven of the 
former to four of the nitrous acid ; at -j- 5 0 (with a trifling al- 
lowance, if any, for a few degrees above or below), three to 
two ; at — 12°, four to jhree, with the mixed acids ; and at 
— so° ? with the diluted vitriolic acid, equal parts. 
