25J: PROCEEDINGS OP THE AMERICAN ACADEMY 



raolybdates. They are, however, very well defined, and usually highly 

 crystalline. In color they vary from an orange to a deep garnet, or 

 ruby red. In general character they closely resemble the salts of the 

 double compounds already described, and are often very beautiful. 



Analytical Methods. — These are for the most part similar to those 

 which I have already described. The three oxides may be precipitated 

 together by raercurous nitrate and mercuric oxide, and then ignited 

 with sodic tuugstate in the manner described for the analysis of 

 phospho-molybdates and arsenio-molybdates. The phosphoric oxide 

 cannot be determined with accuracy by direct precipitation with mag- 

 nesia-mixture. It is necessary first to remove the vanadic oxide. 

 This may be done by dissolving the salt, adding ammonia in small 

 but distinct excess, and afterward ammonic nitrate in large quantity. 

 The" solution is to be boiled for a short time, care being taken that 

 after boiling free ammonia shall still be present. After standing in 

 the cold for twenty-four hours the precipitated ammonic meta-vanadate 

 may be filtered off, washed with a cold concentrated solution of ammo- 

 nic nitrate, and titrated in the manner which I have described in 

 speaking of the vanadio-molybdates. In the filtrate from the meta- 

 vanadate phosphoric oxide may be determined by double precipitation 

 with magnesia-mixture and final treatment with ammonic sulphide. 

 Molybdic oxide is best determined by difference, the sura of the 

 weights of the three oxides being known. Water, ammonia, and basic 

 oxides may be found by the methods which I have already described 

 in the cases of the binary compounds. 



48 : 2 : 1 Series. — When 10 : 2 acid phospho-molybdate of am- 

 monium, 10 M0O3.2 P2O5.5 (NH4).,0-f-G ^1"> ^^^^ ammonic meta- 

 vanadate are dissolved together, there appears to be no reaction ; but 

 if a small excess of chlorhydric acid is added, and the solution is boiled, 

 a beautiful deep orange-red crystalline precipitate is formed at once. 

 This may be drained on a filter and washed with cold water, in which 

 it is but slightly soluble. Hot water dissolves it rather more freely, 

 but the salt cannot be purified by recrystallization, as it is more or 

 less completely decomposed by solution. Ammonia water dissolves 

 it, forming a colorless liquid, in which baric acetate produces a nearly 

 colorless precipitate. Of this salt, — 



1.3011 gr. lost on ignition with WO^Nao 0.1399 gr. = 10.75% 



^'Hg + H„0 

 1.0425 gr. lost on ignition with WO^Na^ 0.1124 gr. = 10.78% 



NH3 + H,0 



