19 a Mr. J. Davy’s Account of some Experiments on the 
reduced, by means of a mixture of snow and muriat of lime, 
the temperature of all these substances 20 degrees below the 
zero of Fahrenheit’s thermometer, but without affecting their 
liquidity. 
The influence of atmospheric air on the compounds of the 
metals and chlorine at high temperatures is curious, and wor- 
* thy of particular attention. The combinations of chlorine with 
lead, zinc, copper, and bismuth, appear to be volatile in open 
vessels, and fixed in closed ones. How moist air operates in 
these instances, it is difficult to say. In other cases, where it 
evidently acts chemically, the changes explain themselves ; 
thus, when the compounds of iron and chlorine and of man- 
ganese and chlorine are heated in the open air, hygrometrical 
water of the atmosphere seems to be decomposed, as muriatic 
acid fumes are produced, and oxides of the metals formed. 
Probably the volatility of the other compounds is connected 
with similar circumstances. This action of moist air has 
hitherto been much neglected ; it is certainly worthy of being 
more fully inquired into, both in a theoretical and practical 
point of view. Its importance in practice is exemplified in the 
reduction of horn silver, and in the formation of several of 
the compounds of chlorine and the metals ; if moist air be 
admitted in these operations, the silver will be lost, and the 
compounds not formed. 
Guided by analogy, I have been led to try whether the 
muriat of magnesia, which is readily decomposed by heat in 
the open air, would not, when the air was excluded, by intro- 
ducing it into a glass tube with a very small orifice, afford a 
permanent compound. The result was agreeable to my ex- 
pectations; I obtained, by strongly heating the muriat for a 
