OF ARTS AND SCIENCES. 73 



Rammelsberg gives these figures as the means of several analyses 

 which agree well with each other, but it must be admitted that a 

 closer correspondence with the percentages required by the formulas 

 would have been desirable. The comparison is not given in his 

 paper. The air-dried salt loses all its water over sulphuric acid. The 

 three atoms of basic water, if we assume their existence, must there- 

 fore be united by a very feeble affinity. Rammelsberg has also 

 analyzed the corresponding potassic salt of the same series. I here 

 give his results, for the sake of comparison with the formula : — 



This salt loses all its water between 120° and 140°. In judging 

 the results of these analyses, as well as of those which I have given, 

 it must be carefully borne in mind that the salts themselves cannot be 

 recrystallized, and that consequently their absolute purity cannot be 

 guaranteed. Moreover, if — as I believe I have shown — there are 

 very similar salts which represent three series in which the ratios of 

 the molybdic and phosphoric oxides are respectively as 24 : 1, 22 : 1, 

 and 20: 1, we may, at least occasionally, have mixtures of the salts of 

 three, or of any two series. The difficulty here is precisely that which 

 occurs in the case of the phospho-tungstates. 



44 : 2 Acid Potassium Salt. — This salt was prepared by boiling 

 a mixture of potassic molybdate and phosphate with nitric acid in 

 excess, when a beautiful yellow crystalline powder separated. Thia 

 was washed with cold water and dried on woollen paper. Of this 

 salt, — 



0.9850 gr. lost on ignition 0.0521 gr. = 5.28% water. 



0.8983 gr. gave 0.7943 gr. Mo0 3 -4- P 2 5 = 88.42% 

 2.0617 gr. gave 0.1201 gr. P 2 7 Mg 2 = 3,72% 



These analyses lead to the formula 



44 Mo0 3 . 2 P 2 0. . 5 K 2 . H 2 + 21 aq, 

 or 



22 MoO, . P 2 5 . 3 K 2 -f 22 MoO, . P 2 0, . 2 K.0 . H,0 -f 21 aq, 



which requires : — 



