5 34 MM. Svanberg ««rf Struve on the Atomic Weight 



there is immediately a disengagement of water ; and the action 

 of the sulphuretted hydrogen is so energetic, that when the 

 current of gas is not too rapid, all the sulphuretted hydrogen 

 is absorbed. The experiment lasts very long; at first a small 

 spirit-lamp suffices, but gradually the temperature must be 

 increased, and, finally, the strongest heat which an Argand 

 lamp can give must be used. It appears that at first an oxysul- 

 phuret is formed, which is very difficult to decompose. After 

 the operation had been continued for twenty-one hours, no 

 further formation of water could be observed ; but neverthe- 

 less no two weighings agreed. The difference between two 

 weighings amounted to as much as 0*0006 grin. At the time 

 we were unable to explain the cause of these differences, but 

 we subsequently discovered it and shall allude to it in the 

 following experiments. 



When the reduction-tube had become perfectly cold, the 

 sulphuretted hydrogen in it was expelled by dry air, and it 

 was then weighed as quickly as possible ; two successive weigh- 

 ings gave 3*0545 and 3'0551 grms. ; the mean of the two is 

 30548. 



Assuming that in this experiment the whole of the molybdic 

 acid has been converted by the action of the sulphuretted hy- 

 drogen into sulphuret of molybdenum MoS 2 , we find the atomic 

 weight of molybdenum by the following equation, in which 

 the atomic weight of sulphur is admitted to be 200*75, and 

 also 200 : 



2-739 : 3*0548 = x + 300 : x + 401*5 



x = 580*336 ;. 

 or 



2-739 : 30548 = x + 300 : x 4- 400 



x = 567*231. 



If this result is compared with the theoretical calculation, 

 100 parts of molybdic acid should yield — 



a. b. Found. 



Sulphuret of molybdenum 111-416 111-416 111*529 



We made a similar experiment with molybdic acid which 

 had been prepared from native sulphuret from a different 

 locality, when 2 855 grms. molybdic acid gave 31652 sul- 

 phuret of molybdenum, or 110*865 per cent. Even though 

 this experiment is not perfectly in accord with the preceding 

 one, it at all events proves the identity of different molybdic 

 acids. 



