COMBINATIONS OF OXIMURIATIC ACID AND METALS. 127 



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 Action of 

 hitherto been much neglected ; it is certainly worthy of being "o^unr"^ '°** 

 more fully inquired into, both in a theoretical and practical 

 point of view. Its importance in practice is exemplitied 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 Action of heat 

 muriate of magnesia, which is readily decomposed by heat in ^mja^^ ^f **" 

 the open air, would not, when the air was excluded, by intro- magnesia, 

 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 muriate for a 

 quarter of an hour, a substance like enamel in appearance, 

 being semifused, and which appeared to be a mixtnie of mag- 

 nesia and the true compound of magnesium and chlorine, for 

 heated with water magnesia was separated, and a muriate of 

 magnesia formed. 



5, On the Relation between the Proportion of Oxigen and Chlo- 

 rine in Combination with several Metals. 

 Errours being very common in chemical analyses, even in Doctrine of 

 those conducted most skilfully and carefully, all possible means pordons aTest 

 should be taken to discover them ; and no means, I think, pro- of the accu- 

 raise to be more efFectual for this purpose, than the general [\7j ^^ ^"'' 

 analogy of definite proportions. From a great variety of facts, 

 it appears that oxigen and chlorine combine with bodies iu 

 the ratio of 7-5 to 33-G. With 1 part by weight of hidro- 

 gen, for example, 7-5 of oxigen unite to form water j and 

 33-6 of chlorine unite with the same proportion to produce 

 muriatic acid gas. To judge therefore of the accuracy of the 

 analyses of the preceding coinbinalions of the metals and 



chlorine. 



