112 PROCEEDINGS OF THE AMERICAN ACADEMY 



MOXOMETAPHOSPHO-TUNGSTATES. 



In joreparlng the salts of this series I have employed ordinary glacial 

 phosphoric acid, which, according to Brescius,* contains ahout 50^ 

 of sodic metaphosphate, and which may be regarded as a mixture 

 of sodic metaphosphate and metaphosphoric acid. I have assumed 

 that the acid is here in the form of monometaphosphoric acid, although 

 upon this point the evidence is still insufficient. As the relations of 

 metaphosphoric acid to indicators of various kinds have not hitherto 

 been studied, the following brief note may be of interest. A solution 

 of glacial phosphoric acid is neutral to tropn?olin. The same solution 

 required for equal volumes with purpurin 23 cc. sodic hj'drate solu- 

 tion ; with htematoxylin, 14 cc. ; and with alizarin, 12.5 cc. No definite 

 end reaction could be obtained with phenol- phthalein, methyl-orange, 

 or rosolic acid. 



Monometaphospho-tungstates are formed by the direct action of the 

 acid upon acid tungstates. They are, frequently at least, gummy 

 uncrystalline bodies. When crystalline the crystals are usually soft, 

 and pack together i-eadily. The salts of the alkaline earths are usu- 

 ally more or less distinctly crystalline. Those of the heavy metallic 

 oxides are often pasty, and sometimes oily. They are not very readily 

 converted into orthophospho-tungstates, and in this respect they seem 

 to differ materially from the corresponding metaphospho-molybdates. 



Analytical Methods. — In these salts tungstic and metaphosphoric 

 oxides may be precipitated together by mercurous nitrate and mercuric 

 oxide. Metaphosphoric acid may be converted into orthophosphoric 

 acid by dissolving the salt in the least possible quantity of water, adding 

 strong sulphuric acid, evajjorating the solution nearly to dryness, and 

 repeating this process several times. This method is very much better 

 than fusion with alkaline carbonates, which effects the transformation 

 of metaphosphoric acid in a very imperfect manner. I believe that I 

 can assert with entire confidence, that in the class of monometaphospho- 

 tungstates the conversion of the metaphosphoric into orthophosphoric 

 acid is much more difficult than in the metaphosphates. The precipi- 

 tation of the orthophosphoric acid by magnesia-mixture must of course 

 be repeated twice. 



24 : 2 : 3 Potassie Monometapliospho-tungstate. — When a cold freshly 

 prepared solution of glacial phosphoric acid is digested with 10 : 4 

 potassie tungstate, part of this salt dissolves, while the undissolved 



* Zeitsclirift fiir analytische Chemie, vi. 187. 



