on the Production of artificial Cold. 287 
cold was not produced as when this circum (lance did not occur, 
and when the acid was weaker. 'I he fame appearance of 
congelation took place with other proportions of acid and 
water, at other temperatures. 
Mineral alkali, when it retained its water of crydallization, 
added to fome of thefe mixtures heightened their effe&s. But 
when it had lod this water, it rather produced heat than cold ; 
and the fame thing is alfo true of Glauber’s fait. This cir- 
cumdance leads us, in fome meafure, to the theory of thefe 
phenomena. Water undoubtedly exids in a folid date in cry- 
dais ; it mud therefore, as in other cafes, abforb a determi- 
nate quantity of fire, before it can return to its liquid date. 
On this depends the difference between Glauber’s fait and 
fodil alkali in their different dates of crydallization and efflo- 
refcence. The fame circumdance too enables us to underdand 
the great effect of Glauber’s fait, which, as far as I recoi- 
led, has the greated quantity of water of crydallization. 
Thofe, therefore, who (hall choofeto purfue the path which 
Air. Walker has opened to them, would do well to try com- 
binations of falts containing much water of crydallization ; 
but they mud take care led the effect (hould be diminiflied or 
dedroyed by the formation of compounds that fix a fmaller 
quantity of fire. It is, however, but judice to Mr. Walker 
to obferve, that he has carried his experiments in this way 
very far, and with great ingenuity. 
I have the honour to be, &c. 
THOMAS BEDDOES. 
T t 2 
