of Molybdenum and some of its Compounds. 541 



stals resembling iodine. The fragments of charcoal were coated 

 with a black crust ; and on allowing the tube to cool, its whole 

 length was covered with a yellowish crystalline mass which 

 did not appear to be very volatile. Of these compounds, 

 which we will designate by the letters A, B, C, and D, 

 A consists of biacichloride, gives a clear solution with water, 



and deliquesces in the air; 

 B appears in fine, dark brown, shining needles, gives with 



water a blue solution, from which ammonia precipitates a 



brownish red oxide ; 

 C is not altered by exposure to the air, possesses a black 



colour, is very slightly and slowly acted upon by alkalies, 



and insoluble in water; 

 D is readily soluble in water; the solution gradually becomes 



blue, but nothing is precipitated by ammonia. 



These statements, which are in the highest degree imperfect, 

 are merely intended to show that we know very little of the 

 chlorine compounds of molybdenum, and that the subject 

 requires a thorough investigation. 



Experiments with Sulphur et of Molybdenum. 



Starting from the fact that sulphuret of molybdenum, when 

 heated with sufficient access of air, is gradually oxidized and 

 converted into molybdic acid, we imagined that if we were 

 able to prepare artificially a pure sulphuret of molybdenum 

 with exactly the same composition as the native mineral, and 

 converted this by roasting completely into molybdic acid, 

 which remains, and into sulphurous acid, which is volatilized, 

 it was to be expected that an accurate atomic weight of molyb- 

 denum might be calculated from the difference in weight of 

 the sulphuret of molybdenum employed. No objection can 

 be urged to this method a priori; it is simple, and the simpler 

 an analytical method the more certain the result in general. 

 If we assume that the oxidation can be effected completely, 

 the method consists in three weighings : — 1, counterpoising the 

 glass tube in which the roasting is to be effected ; 2, weighing 

 with the pure sulphuret of molybdenum ; and 3, weighing the 

 molybdic acid obtained. We shall now prove that our theory 

 was correct, and that we have succeeded in determining with 

 certainly the atomic weight of molybdenum based upon the 

 atomic weight of sulphur. 



The artificial sulphuret of molybdenum was prepared ac- 

 cording to the method described in the first part of this inves- 

 tigation for obtaining pure molybdic acid, with this difference 

 only, that the sulphuret was dried over sulphuric acid under" 



