84 ATOMIC WEIGHT DETERMINATIONS. 



phide by roasting it first in a current of moist, and then of 

 dry air. Three experiments were excluded as imperfect. 

 The remainder gave a mean of 89.7523 molybdic acid from 

 100 sulphide ; extreme difference, 0.22. The value follows 

 for S = 200. Objections have been made [Liebig's Aim., 

 68, 211) that the dift'erence in weight between the acid and 

 the sulphate is too small for the purpose of the determina- 

 tion, and that the different analyses give very different 

 atomic weights. The sulphide was prepared by melting 

 together molybdic acid, sulphur, and caustic potash, and 

 leaching the product with water and chlorhydric acid. The 

 sulphide was dried in a current of hydrogen. The molyb- 

 dic acid was dissolved in ammonia to prove the absence of 

 sulphide. [Urdmann's Journ.fUr Prak. Chem., 4~^, 1848, 315.) 



N. J. Berlin : 91.96 (0 = 16) ; 574.75 (0 = 100). 



Determined by four analyses of the double mono-sesqui- 

 molybdate of ammonium by heating gently with nitric acid 

 in a platinum crucible until only molybdic acid was left. 

 Extreme difference, 3.32 for O = 100 ; N" = 175 ; H = 12.5. 

 The preparation of the salt is not given. {Erdmami' s Journ. 

 filr Prak. Chem., 4,9, 1850, 446.) 



J. Dumas : 96 (O = 16). 



Dumas made five experiments on the reduction of molyb- 

 dic acid (prepared from the natural sulphide) by means of 

 hydrogen. The reduction was begun at a low temperature 

 in a glass tube, and completed in an unglazed porcelain tube 

 in a reverberatory furnace, where it was kept till several 

 hours heating produced no further alteration in weight. 

 The molybdenum did not assume a metallic appearance. 

 The number is the mean ; extreme difference, 0.8 for = 

 16. {A7inal. de Chim. et de P/ujs., (3,) ^5, 1859, 142.) 



M. Delafontaine : 92 (0 = 16); 575 (0 = 100). 



This chemist made many experiments in various ways 

 without being able to reach constant results, and only re- 

 marks that his experiments indicate Svanberg and Struve's 

 value as the best. [Erdmaiin's Journ. fur Prak. Chem., 95, 

 1865, 137; Bibl. Univ., Arch, des Sciences, 23, 1865.) 



H. Debray: 95.94 (O = 16). 



Debray made three experiments on the reduction of 

 molybdic acid. The acid was first converted into the red 



