Production of artificial Cold. 397 
reduced, and then adding the falts, a much greater degree of 
cold might be produced ; but, by various diverged trials, I 
found but little advantage gained; I fhall therefore forbear 
mentioning the particulars. In the courfe of this winter, 
1'ome diluted nitrous acid, in a wide-mouthed phial, was im- 
merfed in a freezing mixture; when cooled to about -32 0 , it 
froze intirely to the confidence of an ointment, when the ther- 
mometer fuddenly rofeto — 2 ; on adding home fnow that lay 
by me, it became again liquid, and the mercury funk into the 
bulb of a thermometer graduated to - 76° : I know not its 
exact ftrength ; but by the effect imagine it might correfpond 
nearly with that which is capable of the eafied point of fpi- 
rituous congelation. Cold, I have found, may be produced 
by the union of fuch falts as on mixing are decompofed, and 
become liquid or partially fo. The mineral alkali produces 
this effect with all the ammoniacal falts ; but with nitrated 
ammonia to a confiderable degree. The mineral alkali added 
in powder to nitrous acid, diluted as above, funk the thermo- 
meter twenty-two degrees only, from 53 0 (temperature of air 
and materials) to 31 0 . This fait contains nearly as much 
water of cryflallization as vitriolated natron, and produces 
more cold during folution in water than that fait. The reafon 
why it produces lefs when added to acid than the neutral fait 
does, is perhaps fufficiently evident. I have obferved the ther- 
mometer to be ftationary, or even to rife, during the violent 
efFervefcence produced 011 mixing thofe materials, and to link 
as foon as that ceafed. 
Vitriolated natron diflblved indifferently in rectified fpirit of 
wine, and produced neither heat or cold ; the difpofition to 
produce cold, during its folution, being perhaps exactly coun- 
teracted by the tendency which the difi'olved fait hath in 
G g g 2 uniting 
