532 MM. Svanberg and Struve on the Atomic Weight 



Jybdenum requires, therefore, further experiments. It is pro- 

 bable that molybdic acid may be reduced by hydrogen, and 

 then the atomic weight might be obtained with tolerable ac- 

 curacy, especially if the acid after being weighed was saturated 

 with ammoniacal gas to prevent its volatility, the ammonia 

 salt decomposed by heat, and the residual fixed oxide ignited 

 in hydrogen." 



It is seen, therefore, that Berzelius places no great reliance 

 upon his determination, which, moreover, is based upon oue 

 single experiment; and it is remarkable that he should have 

 deduced the number 596-101, which differs but very little 

 from the atomic weight we have found. As Berzelius points 

 to the reduction of molybdic acid by hydrogen, we began with 

 this experiment; we shall now proceed to describe it. 



Action of Hydrogen upon Molybdic Acid. 



Experiment I. — Molybdic acid was heated in a reduction- 

 tube in a current of dry air, to deprive it of all moisture, and 

 to be certain that the whole of the molybdenum was in the 

 state of molybdic acid. We may observe that molybdic acid 

 is not a very hygrometric substance. 



3*0388 grms. of this molybdic acid were heated in a current 

 of hydrogen over an ordinary spirit-lamp. Reduction imme- 

 diately ensued, a large quantity of water was given off', which, 

 however, soon decreased, and in the course of an hour and a 

 half had almost entirely ceased. When this point had been 

 attained, the tube was allowed to cool, the hydrogen in it ex- 

 pelled by dry air, and the residue weighed; it amounted to 

 2*68<t6 grms., and was reddish-brown. Upon this the re- 

 duction was continued with an Argand lamp, when again 

 considerable quantities of water were given oft"; and although 

 the reduction was continued for eight hours under these 

 conditions there was still a deposit of water. By this con- 

 tinued intense red heat the glass had gradually become so 

 brittle and crystalline that the tube on cooling cracked. 

 The contents of the bulb were partly brown, partly gray, 

 and had a metallic lustre. The acid employed for the ex- 

 periment had lost, according to the first weighing, 0*3548 

 oxygen, or 11*656 per cent. ; but this result agrees tolerably 

 well with the supposition that the molybdic acid, on reduction 

 with hydrogen at a low temperature, loses 1 atom oxygen 

 antl is converted into the oxide which Berzelius calls oxide of 

 molybdenum. But it may also be conceived that 2 atoms 

 molybdic aciil = 2MoO :i are converted into molybdate of the 



