540 MM. Svanberg and Struve on the Atomic Weight 



H. Rose, who first quantitatively examined this compound 

 and determined its formula, found in two analyses 34*295 and 

 35*001 per cent, chlorine. 



This biacichloride of molybdenum forms yellowish-white 

 shining laminae, which exhibit no crystalline form even with a 

 compound microscope. 



We have prepared the biacichloride according to this me- 

 thod several times, but have never noticed the simultaneous 

 appearance of any other chlorine compound. Although it is 

 difficult to determine accurately the chlorine, owing to the 

 molybdate of silver accompanying the precipitate, yet we be- 

 lieve that the principal source of uncertainty is to be ascribed 

 to the difficulty of preparing pure biacichloride. This com- 

 pound is generally mixed with traces of molybdic acid, for 

 when perfectly pure, in which state it is only accidentally and 

 very rarely obtained, it dissolves entirely in water, while in 

 general it furnishes an opalescent solution. If this is the 

 correct cause, it is readily explained why H. Rose, as well as 

 ourselves, have found so small an amount of chlorine in the 

 compound. This explanation is further confirmed by the 

 circumstance, that when dry hydrogen is passed over the biaci- 

 chloride and the bulb gently heated, nearly the whole of the 

 chlorine compound is volatilized ; but a small residue is left, 

 which most probably consists of the molybdic acid contained 

 in the biacichloride. 



As we could not obtain a satisfactory result from the ana- 

 lysis of the biacichloride, we made the following experiment 

 to obtain some other chloride. 



A glass tube about 2 feet long, curved somewhat anteriorly, 

 was filled, first with a considerable stratum of well-calcined 

 fragments of charcoal, and then with a mixture of molybdic 

 oxide and charcoal powder which had been previously well 

 calcined ; the straight end of the tube was connected with a 

 chlorine apparatus, and dry chlorine passed for a considerable 

 time through it. That part of the tube with the charcoal was 

 now heated until the charcoal was incandescent, when the 

 other portion of the tube containing the mixture was gradually 

 heated to redness. The current of chlorine was continued 

 during the whole operation ; it was rapidly absorbed and 

 various chlorine compounds formed, of which we were able to 

 distinguish the following: — 



The most volatile compound which condensed in the most 

 anterior curved part of the tube was the biacichloride of mo- 

 lybdenum ; the quantity was small; immediately behind this 

 was the compound described by Berzelius under the name of 

 chloride of molybdenum ; it formed dark brown, shining cry- 



