On definite Proportions. 341 



XIII. Additions to the foregoing Sections, 



iRelatina to the Sidplmret arid the Oxides of Lead, and to 

 the Sulphuric Add. Extracted by Gilbert from a 

 Manuscript Communication of the Author. 

 In order to obtain lead perfectly pure, I repeatedly dis- 

 solved and crystallized the nitrate of the protoxide, until 

 the mother liquor, when slowly evaporated, remained per- 

 fectly white, and, when digestea with carbonate of ammonia, 

 exhibited no copper upon passing sulphuretted hydrogen 

 through the fluid. Frequently after tlirce crystallizations 

 decided marks of copper were observed. The purified salt. 

 mixed u ilh charcoal dust, was burnt in a Hessian crucible, 

 and the lead obtained, in order to free it from the carbon 

 adhering to it, was kept for some time ignited. When 

 dissolved in the nitric acid, it exhibited no marks of the 

 presence of any foreign substance. 



A. Sulphuret of Lead. 



Twenty-five grammes of this lead, in small pieces, were 

 put into a glass flask with a narrow mouth, with ten gr. 

 of sulphur, which had been kept for half an hour in fusion 

 over a spirit-lamp, and which was introduced while still 

 fluid ; they were heated slowly until the gl;iss began to 

 melt, the opening of the flask being closed, when no more 

 sulphureous fumes appeared, with a stopple of charcoal. 

 The sulphuret, which had assumed a crystalline form and a 

 metallic splendour, weiijhed 28-835 gr.; so that 100 parts 

 of lead had taken up only 13-42 of sulphur. I therefore 

 jmacincd that all the lead had not combined with the sul- 

 phur ; and taking ten sirammes of the compound, I mixed 

 them very carefully wiili pure and dry sulphur, and heated 

 them together in a smaller flask, until the glass was soften- 

 ed : but they neither acquired nor lost any weight. 



The experiment was repeated with 13 gr. of lead, whence 

 I obtained 1 7'3 12.*) of sulphuret. Upon another repetition 

 it afforded 17'31 gr. of the sulphuret. Consequently ac- 

 cording to these txpcriments, which agree perfectly with 

 each oilu-r, the snlphuret of lead contains - 



Sulphur i3-s0 13-42 1000 



Lead.. 86- ;4 100 OO 648-5 



Notwiihslandmg this agreement, it is still very possible 

 that the quantity of sulphur is here represented as too small, 

 since in so strong a heat it was impossible lo keep the ves- 

 sels air-tight. In my earlier experiments, I found that 100 

 parts of lead look up from 15-53 to 15-50 of sulphur. The 

 Y 3 sulphuret 



