Mr. Walker’s Experiments on the 
uniting with the fpirit to produce heat. Vitriolated mngnefia 
(a fait very fimilar to vitriolated natron) during folution in the 
diluted nitrous acid, produced nearly as much cold as that 
lalt : the {mall difference there is between them, as to this 
effect, may be owing to the former containing rather lefs 
water in its crvftals. 
j 
Vitriolated natron, liquified by heat, was fet to cool ; when 
its temperature was reduced to 70°, it became folid, and the 
thermometer immediately rofe to 88° (eighteen degrees) its 
freezing point. Does not the quantity of feniible heat evolved 
by this fait, in becoming folid, indicate its great capacity for 
heat, in returning to a liquid date, and confequently account 
in a great meafure for its producing fuch intenfe cold during 
folution in the diluted mineral acids ? Two falts, vitriolated 
argillaceous earth (alum) and tartarized natron (Rochelle fait), 
each contain nearly as much water of cryftallization as vitrio- 
lated natron ; but produced neither of them any confiderable 
effeft during folution in the diluted nitrous acid ; the latter 
made the thermometer rife : neither did their temperatures in- 
creafe, like that fait, in changing from a liquid to a folid 
Rate. 
From the obvious application of artificial frigorific mixtures 
to ufeful purpofes, in hot climates efpecially, where the inha- 
bitants fcarcely know by the fenfe of feeling winter from fum- 
mer, it may not be amifs to hint at the eaiieft and moft 
(economical method of ufing them. For moft intentions, 
perhaps, the following cheap one may be fufficient : of 
lfrong vitriolic acid, diluted with an equal weight of water, 
and cooled to the temperature of the air, any quantity ; add to 
this an equal weight of vitriolated natron in powder : this is 
the proportion when the temperature fet out with is + 50% 
2 and 
