1835.] and Analysis of the Vanadiate of Lead. 43 



supposing it deprived of all moisture and free sulphur 1*04 

 grains = 24*98 grains sulphuret of lead. 9*6 grains of the 

 heated sulphuret were digested in nitric acid, with a drop 

 or two of sulphuric acid. The resulting precipitate was 

 thrown on a filter. After edulcoration and heating, it 

 weighed 11*56 grains sulphate of lead. Hence, 24*98 grains 

 sulphuret of lead in this case are equivalent to 30*08 grains 

 sulphate of lead, and in the latter are contained 22*164 

 grains protoxide of lead. 



I have adopted the method of determining the quantity 

 of lead contained in the mineral, by converting the sulphur 

 into sulphuric acid, and obtaining the lead in the state of a 

 fixed salt, because it appears to be more free from objections 

 than when the proportion of lead is calculated from the 

 precipitated sulphuret of lead, whose definite composition 

 after exposure to a considerable temperature might be 

 called in question. For in this experiment which was 

 made with great care, the proportion of oxide if estimated 

 from the sulphuret would amount to 23*314 grains. 



According to M. Fournet, sulphuret of lead when exposed 

 to a strong heat, volatilizes in the manner which is precisely 

 exhibited by the following formulae : 12 Pb + 24 S m (4 

 Pb + 8 S + (8 S)J where the portion 8 S separates at 

 first followed by 4 Pb + 8 S leaving 8 Pb + 8 S which 

 by a continued heat loses ( 2 Pb + S) + 2 Pb + 4 S* 



Through the solution filtered from the sulphate of lead 

 a current of sulphuretted hydrogen was passed, but without 

 effecting any precipitation or colouration, indicating the 

 absence of arsenic in the mineral. I am disposed to con- 

 sider the impurities which have been observed in some 

 analyses, as proceeding from the portions subjected to ex- 

 amination having been mixed with the base upon which the 

 mineral was placed. In some of the specimens which I 

 examined, the phosphate and arseniate of lead, forming the 

 seat of the vanadiate of lead, extended above the base of the 

 mamillary masses towards their interior, but as they differed 

 very considerably in colour, the separation of the latter 

 from the former was easily accomplished. 



The liquid after the separation of the sulphuret of lead was 

 evaporated. It assumed a blue colour, and when only a small 

 portion of fluid remained it gradually became green, and on 



* Annates de Chimie et de Physique, lv. 413. 



