of Molybdenum and some of its Compounds. 545 



merits; but if, starting from this, we wish to calculate the atomic 

 weight of molybdenum, it must be based upon the number 

 representing the atomic weight of sulphur. Berzelius deter- 

 mined the atomic weight of sulphur to be 200*75, by convert- 

 ing a known weight of chloride of silver into sulphuret. 

 Erdmann and Marchand have arrived at the number 200*000 

 by the analysis of the sulphuret of mercury. The starting- 

 point for Erdmann and Marchand's number is not only de- 

 pendent on the atomic weight of mercury, but the most 

 important question is, Were these chemists perfectly certain 

 that the sulphuret of mercury was free from any mechanical 

 admixture of metallic mercury? As this was not ascertained, 

 we do not think that the atomic weight of sulphur found by 

 them, although highly probable, can be admitted uncon- 

 ditionally. With regard to Berzelius's atomic weight for 

 sulphur, it is liable to the objection, that perhaps a minute 

 quantity of chloride of silver surrounded by sulphate of 

 silver was withdrawn from the action of the sulphuretted 

 hydrogen. We therefore treated 5*5967 grms. chloride of 

 silver with sulphuretted hydrogen and obtained 4*8395 sul- 

 phuret of silver. Whence, admitting Berzelius's atomic 

 weights for chlorine and silver, that of the sulphur is found 

 to be 200*71 ; but on dissolving the sulphuret of silver in 

 pure nitric acid, a small quantity of undecomposed chloride 

 of silver remained undissolved, and, consequently, the number 

 200*71 must be too high. We wished to decide this im- 

 portant question, but have been prevented by various circum- 

 stances, and, on that account, all the theoretical calculations 

 we have made, and also that of the equivalent of molybde- 

 num, have been calculated with the two different atomic 

 weights for sulphur. 



Now, if we calculate the equivalent of molybdenum from 

 the quantity of molybdic acid which we obtained from 100 

 parts of sulphuret of molybdenum, we have, when the atomic 

 weight of sulphur is assumed to be 200*75, — 



100 : 89*7523 = x + 401-5 : x + 300 



x = 588*966 (a.) 



and when the atomic weight of sulphur is 200000, — 



100 : 89*7523 = x + 400 : x + 300 



x = 575*829 (b.) 



Although the difference between the two atomic weights here 

 assumed for sulphur is not very great, its influence in calcu- 

 lating the atomic weight of molybdenum is very considerable, 

 the difference between a and b amounting to more than 13 



