530 MM. Svanberg and Struve on the Atomic Weight 



and the anhydrous salt — 



I. II. 



Baryta 51'009 51 '366 



Molybdic acid \ AQ . n ,„ 47*530 



Phosphoric acid J ' ' W04 



These numbers almost coincide with those found with the 

 neutral molybdate of baryta, described in the first part of this 

 paper. 



From the analyses of these salts and the phaenomena de- 

 scribed, it is quite evident that but a very small quantity of 

 phosphoric acid is contained in combination with molybdic acid, 

 and that its amount is apparently variable. Hence arises the 

 question, What part does the phosphoric acid act in these 

 compounds, and how are we to view the molybdic acid thus 

 metamorphosed ? Can we admit a different allotropic state 

 in this molybdic acid ? and should we distinguish it from the 

 ordinary molybdic acid by the sign of 6-molybdic acid? 



We have made numerous experiments to convert molvbdic 

 acid into this different state by means of other bodies besides 

 phosphoric acid. It is unnecessary to relate the experiments, 

 as we came to the result, that, when perfectly pure molybdic 

 acid was employed, in which the absence of phosphoric acid 

 had been ascertained, no change could be effected. But the 

 tendency of phosphoric acid to produce yellow precipitates 

 or yellow solutions with molybdic acid is so great, that we 

 look upon molybdic acid as the most sensitive test for phos- 

 phoric acid, since in cases in which we obtained mere in- 

 distinct signs of the presence of phosphoric acid by other 

 reagents, the reaction with molybdic acid was quick and per- 

 fectly distinct. 



Phosphoric acid, which acts so important a part both in the 

 vegetable and animal organism, we have found, with the as- 

 sistance of this reaction, to be most generally distributed in 

 nature. All the rocks, all the felspars which we have exa- 

 mined, contain phosphoric acid, and to prove this by means 

 of molybdic acid is exceedingly simple. The sulphuret of 

 molybdenum which we used in our investigation was remark- 

 ably pure • only minute traces of gangue, consisting of frag- 

 ments of quartz and felspar, were here and there perceptible, 

 but the molybdate of ammonia prepared by roasting this 

 mineral and exhaustion with ammonia contained a little 

 phosphoric acid. To detect this impurity, it suffices to add 

 to the concentrated solution of the salt an excess of muriatic 

 or sulphuric acid, when instantly the solution assumes a 

 yellow colour, and deposits in the course of a few minutes a 

 yellow precipitate of b- molybdate (phosphomolybdate) of 

 ammonia. Or if we take the alumina which has been obtained 



