87fl On definite Proporttoni. 



tains, according to the experiment, 30*49, and according 

 to the calculation, 30-1 cf oxvuen. Since 100 parts oF 

 muriatic acid take up the same q.iantitv ot oxvgen in the 

 oxide of lead as in the two dcarees of oxidation ot copper, 

 the proposition already laid down is further confirmtd by 

 this agreement. 



I must however here confess the existence of an irrogir- 

 larity, which [ cannot yet explain, but which supposes an 

 inaccuracy in some of (hose experiments which 1 thought 

 the most unexceptionable. 



A hundred parts of muriatic acid are saturated by 434-8 

 of oxide of silver, which contain 31 '9 of oxvgen. Now, 

 since the analyses of the oxide and the muriate of lead, 

 and especially that of the muriate of silver, seem to be of 

 such a nature as to be susceptible of accuracy, and since 

 they are also confirmed by other tests which serve as checks 

 to verify them, I am utterly unable to discover on what the 

 principal error can possibly depend. Does the salt of itiver 

 contain water ? I have mched it in a red heat, withoiri 

 any loss of weight. Is the oxygen of the lead assumed be- 

 low the truth ? I refer to the experiments on the sulphate 

 ot lead, the second of which was occasioned precisely by 

 this question ; here it appeared that 100 parts of lead, with 

 sulphuric acid, afforded exactly as much sulphate as IQJ'S 

 of the oxide of lead. Or, is the analysis of the muriate of 

 lead inaccurate ? This supposition is contradicted both by 

 the result of the calculation, which agrees sufficiently well 

 with the analysis, and by that of the precipitation with 

 nitrate of silver. The difference of l'4l of oxygen between 

 the oxides of lead and of silver is indeed not Yery consider- 

 able J but it must depend on some unknown circumstance. 



X. Iron and Sulphur. 



It has long ago been demonstrated bv Proust, that several 

 metals may be combmed with sulphur in two proportions, 

 a maximum and a minimum. It appeared to me to be in- 

 teresting to examine, how far inflannnable bodies observe 

 the same laws in their combinations with each other, as 

 with oxygen. ■ Fur this purpose I chose the sulphnret of 

 iron, as being most easily subjected to analysts. 



A. Sulphuret of Iron at a Minimum. 



I mixed one part of pure iron, very nearly free from car- 

 bon, which had been rolled out to the thickness of a leaf, 

 with three of pure sulphur, and heated them in a small 

 glass retort with a receiver luted to it. When the sulphur 



bad 



