6l2 PHILOSOPHICAL TRANSACTIONS. [aNNO I7OI. 



Class II. 0/ Cold Fermejitations. — Saltpetre, cast into its acid spirit, raised 

 some smoke, or vapours, and caused the liquor of the thermometer to descend 

 4 Hues. From saltpetre, mixed with spirit of vitriol, smoke exhaled in great 

 quantity, and caused the liquor to descend from 6 to 7 lines. In these two 

 experiments I put half an ounce of salt upon 3 ounces of liquor. I put half an 

 ounce of sal ammoniac into 3 ounces of spirit of nitre, and the thermometer 

 descended 2 inches 5 lines. This mixture emitted some vapours, which seemed 

 more considerable than those which usually exhale from spirit of nitre alone. I 

 poured half an ounce of sal ammoniac into 3 ounces of spirit of vitriol, which 

 made a violent fermentation. The matter was considerably raised, and much 

 vapour emitted ; the liquor was very thick, and the thermometer descended 3 

 inches 6 lines. I observed, that the vapours which were raised by this mixture 

 were hot, and that they considerably raised the thermometer, which I held hang- 

 ing over the matter, though that which was dipped in it descended, and shewed 

 a very great cold.* Sea-salt mixed with acid spirits, heats the liquors, instead 

 of cooling them. Being mixed with spirit of salt, it raised the thermometer 

 some lines, without showing any sensible fermentation. With oil of vitriol it 

 ferments with a noise, and raises a great smoke : the liquor thickens, and be- 

 comes a sort of a clear jelly. The thermometer rises very much in this mixture, 

 and the heat is sensible to the touch. All the volatile alkaline salts, mixed with 

 different acid liquors, excited a fermentation, more or less strong, according to 

 the acidity of the liquors, and the purification of these salts from their fetid oils. 

 They all made the thermometer descend : but that which did so the most con- 

 siderably, is the salt of urine. One ounce of volatile salt of urine, very well 

 rectified, in 4 ounces of distilled vinegar, made a strong fermentation. The 

 substance is elevated very much, and with noise ; and the thermometer descends 

 in the fermentation one inch Q lines. One ounce of volatile salt of urine, in 3 

 ounces of spirit of vitriol, raised a violent fermentation, during which the ther 

 mometer descended 1 inches 4 lines. The mixture of salt of tartar, or other 

 fixed alkaline pure salts, with acid liquors, excited fermentations with heat. I 

 made all these experiments with the same thermometer, when the weather was 

 sufficiently cold, and the temperature of the air equal enough. 



As to the reason of these experiments, I first of all examined the simple cold 

 solutions; and having, with all philosophers, fixed this principle, that cold is no- 



* Much greater degrees of cold than those here mentioned may be prodciced by employing other 

 saline substances ; such as sulphate of soda and diluted sulphuric acid; sulphate of soda and muriatic 

 acid ; phosphate of soda and diluted nitric acid, &c. When snow can be procured, a mixture of that 

 ■with muriate of lime produces a most intense cold. See the experiments of Mr. Walker of Oxford, 

 insertedin the Phil. Trans, for 1795 and ISO 1. . ,...,.,;.. 



