On Massey's Sounding Machine, 91 



temperatures. I have reduced, by means of a mixture of 

 snow and muriat of lime, the temperature of all these sub- 

 stances 20 decrees below the zero oi Fahrenheit's thermo- 

 ineter, but without affecting their liquidity. 



The influence of atmospheric air on the compounds of 

 the metals and chlorine at high temperatures is curious, 

 and worthy of particular attention. The combinations of 

 chlorine with lead, zinc, copper, and bismuih, 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 manganese and chlorine are 

 heated in the open air, hygrometrical water of the atmo- 

 sphere 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 re- 

 duction 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 ana'ogy, I have been led to try whether the 

 muriat of magnesia, which is readily decomposed by heat 

 in the open air, uould not, when the air was excluded, by 

 introducing it into a glass tube with a very small orifice, 

 afford a permanent compound. Toe result was agreeable 

 to my expectations; 1 obtained, by strongly heating the 

 muriat for a quarter of an hour, a substance like enamel in 

 appearance, being semi- fused, and which appeared to be 

 a mixture of magnesia and the true compound of magne- 

 sium and chlorine; for heated with water magnesia was 

 separated, and a muriat of magnesia formed. 



pro be continued.] 



XVITI. Extract from a Report made to the Rojjal Tnslitvtion 

 on Massky's Sounding Machine, March 4, 1811. 



To Mr. Tilloch. 



Sin, In March 1811, it fell to my lot as chairman of the 

 Committee of Mathemalics and mechanical Inventions at 



the 



