Production of artificial Cold, 3^ 
and will fink the thermometer to 5 0 ; if higher, the quantity 
of the fait muft be proportionably increafed. The obvious 
and bell: method of finding the necefifary quantity of any fait 
to produce the greatefi: effect, by folution in any liquid, at any 
given temperature, is by adding it gradually until the thermo- 
meter ceafes to fink, ftirring the mixture all the while. 
If a more intenfe cold be required, double aqua fortis, as it is 
called, may be ufed ; vitriolated natron, in powder, added to this, 
produces very nearly as much cold as when added to the diluted 
nitrous acid : it requires a rather larger quantity of the fait, at 
the temperature of + 50°, about three parts of the fait to two 
parts of the acid : it will fink the thermometer from that tem- 
perature nearly to o, and the confequence of more fait being 
required is, its retaining the cold rather longer. This mixture 
has one great recommendation, a faving of time and trouble. 
A little water in a phial, immerfed in a fmall tea-cup of this 
mixture, will be foon frozen in fummer; and if the lalt be 
added in cryfials unpounded to double aqua fortis, even at a 
warm temperature, the cold produced will be fufficient to 
freeze water or creams j but if diluted with one-fifth its 
weight of water, and cooled, it is about equal to the diluted 
nitrous acid above mentioned, and requires the fame propor- 
tion of the fait. A mixture of vitriolated natron and diluted 
nitrous acid funk the thermometer from + ~o° (temperature of 
air and ingredients) to + io°. 
The cold in any of thele mixtures may be kept up a long 
time by occafional additions of the ingredients in the propor- 
tions mentioned. A chemifi: would make the fame materials 
ferve his purpofe repeatedly. 
Equal parts of muriated ammonia and nitrated kali in pow- 
der make a cheap and convenient compofition for producing 
cold 
