54-2 MM. Svanberg and Struve on the Atomic Weight 



the air-pump. If this precaution is omitted, by drying it in 

 the air or at 212°, the sulphuret always exhibits an acid re- 

 action, owing to the formation of some sulphate of the protoxide 

 of molybdenum. It soon dried under the air-pump, where it 

 was kept until no further loss in weight could be observed. 

 We thus prepared two different quantities of sulphuret of 

 molybdenum, using the following proportions: — 



For sulphuret A we fused together 4 grms. molybdic acid, 

 8 grms. sulphur, and 6 grms. carbonate of potash ; for the 

 sulphuret B we used 11 grms. trimolybdate of potash, 20 grms. 

 sulphur, and 6 grms. carbonate of potash. 



After we had thus prepared a pure sulphuret, the expe- 

 riments were made in the following manner : — a glass tube 

 provided in the centre with a bulb was stopped at one end 

 with a little asbestos, and the whole then heated to redness in 

 a current of dry air, and when cold counterpoised and the sul- 

 phuret of molybdenum weighed in it. Upon this the bulb with 

 its contents was heated in a current of dry hydrogen, when a 

 small quantity of water was expelled, but we were never able 

 to observe any disengagement of sulphurous acid. But if the 

 sulphuret of molybdenum had not been dried under the air- 

 pump, there was always some sulphurous acid liberated on 

 heating it in hydrogen. When the sulphuret had been per- 

 fectly dried in this manner, the hydrogen was expelled after 

 cooling by dry air and the weight of the sulphuret again 

 determined. The difference between the first and second 

 weighing never amounted to more than from 1 to 2 milligrammes 

 at the furthest. That part of the glass tube in which theasbestos 

 was, was connected with an aspirator, and the bulb heated 

 gently with a small spirit-lamp, ordinary moist atmospheric 

 air, and only at the end of the operation dry air being allowed 

 to pass over the sulphuret. This operation does not require 

 a very high temperature, but the contents of the bulb must be 

 frequently shaken, so as constantly to present fresh surfaces 

 to the reaction, in order that the mass may not cake into one 

 lump. If these precautions are neglected, a portion of the 

 molybdic acid encloses some undecomposed sulphuret and pre- 

 vents the complete oxidation, as we shall show further on. If 

 dry air is allowed to act upon the sulphuret from the very be- 

 ginning of the operation, the roasting is just as complete, but 

 it is slower. The operation, when from 1 to 2 grammes of 

 sulphuret is employed, lasts from two to three hours. It is not 

 advisable to employ larger quantities, as the oxidation is then 

 effected with greater difficulty, and it is impossible to be cer- 

 tain that no portion has escaped decomposition. When 

 the sulphuret was converted into the yellow molybdic acid we 



