210 PROCEEDINGS OF THE AMERICAN aCADEMY 



this point hereafter, and give additional proofs of the twofold mode of 

 combination of hydroxyl. 



Further investigation will almost certainly show that the homologues 

 of hydryl-phosphinic or phosphorous acid will also form complex acids 

 with tungstic and molybdic teroxides. Thus methyl-phosphinic acid 

 {CH„ . PO . (OH) J should form at least one series of each of the 

 general types : — 



m M0O3 . {CH3 . PO . (0H)2} n Hp. 

 n WO3 . {CH3 . PO . (0H)2} p HoO. 



In these cases arsenic, and perhaps antimony, may replace phosphorus. 

 Phosphoroso-tungstates may be formed by the action of phosphorous 

 acid upon acid tungstates. The only salt obtained at present appears 

 to have the formula 



12 WO3 . 2 {H . PO . (OH),} 2 Kp + 12 aq. 



I propose to return to this special point when describing the related 

 groups of arsenoso-tungstates and antimonoso-tungstates and the cor- 

 responding molybdates. In the analysis of the phosphoroso-molybdate 

 of ammonium the phosphorous acid was determined by dissolving the 

 salt in an excess of a solution of sodic carbonate, oxidizing with bro- 

 mine, and precipitating with magnesia-mixture. 



VANADIO-MOLYBDATES. 



The general analogy between vanadic, arsenic, and phosphoric pen- 

 toxides suggested to me the possibility of forming series of vanadio- 

 molybdates and vanadio-tungstates, belonging to types of a character 

 similar to those of the phospho-molybdates and phospho-tungstates 

 already described. I shall now show that such compounds may 

 readily be formed by processes identical in principle with those which 

 yield compounds of phosphoric and arsenic oxides with molybdic 

 teroxide. 



Vanadio-molybdates are formed when vanadic pentoxide VgOj is di- 

 gested with solutions of alkaline molybdates, more especially with the 

 acid salts of potassium, sodium, or ammonium. The solution quickly 

 becomes yellow, then, on heating, orange, and finally passes in many 

 cases to deep orange-red. The vanadic oxide or acid employed must 

 be perfectly free from vanadic dioxide, as this is also readily dissolved. 

 The resulting compound then belongs to the class of triple complex 

 acids, and contains both oxides of vanadium united to molybdic oxide. 

 I shall return to these compounds in due time, and meanwhile shall 



