OF ARTS AND SCIENCES. 51 



the corresponding metallic jjhosphates are boiled with vanadic acid or 

 acid vanadates. As a rule, the salts are beautifully crystalline, and 

 have a yellow or orange-yellow color, passing in some cases to deep 

 orange-red. 



The general characters of the phospho-vanadates are as follows. 

 The alkaline salts have a sulphur-yellow, and in some cases bright yellow 

 color. They are ciystalline and often present minute talcose shimmer- 

 ing scales. The relation of these salts to water is especially remark- 

 able. A small quantity of water simply dissolves the phospho-vanadate 

 with a yellow color ; on adding more water, the solution gradually 

 becomes orange, then orange-red, and finally deep red. Phosphoric acid 

 is set free, and one or more new definite salts are formed, in which the 

 proportion of the vanadic to the phosphoric oxide is largely increased. 

 Precisely similar changes occur in the action of water upon arsenio- 

 vanadates. AYheu the deep red solutions are evaporated, the changes 

 of color described occur again in the inverse order, and finally the 

 original yellow salt is again obtained, though not always perfectly free 

 from the higher compound. The facility with which the salts of this 

 series are decomposed by water makes it often difficult to obtain them 

 in a state of absolute purity, and renders the reactions with metallic 

 salts uncertain as characteristics. When alkaline phospho-vanadates 

 are evaporated with nitric acid, the base is in many cases entirely 

 separated, and phospho-vanadic acid remains in solution and may 

 separate in crystals. This separation of fixed base often takes place 

 in presence of an excess of phosphoric acid alone. Solutions of alkaline 

 phospho-vanadates appear to be partially reduced by dust or traces of 

 organic matter with exceptional facility. In such cases the solutions 

 take a more or less distinct greenish color, and phospho-vanadico- 

 vanadates are formed. The solutions of these last salts are not very 

 easily oxidized by bromine or nitric acid, and it is therefore advisable 

 in preparing phospho-vanadates to avoid as much as possible the 

 presence of reducing agents. Alkaline phospho-vanadates dissolve 

 readily in hot solutions of acid tungstates and molybdates, forming 

 orange or orange-red solutions, which yield in many cases beautiful 

 crystalline phospho-vanadio-niolybdates and phos[)ho-vanadio-tungs- 

 tates. 



Analytical Methods. — The method usually adopted for the separa- 

 tion of vanadic and phosphoric oxides by means of ammonic chloride 

 may be successfully applied to the analysis of the phospho-vanadates. 

 A small excess of ammonia is to be added to the solution of the salt, 

 which is then to be heated until it becomes colorless. In this manner 



