GQ PROCEEDINGS OF THE AMERICAN ACADEMY 



The determination of the sum of the water and ammonia must in 

 this case be corrected for the oxygen required to convert the 21.22% 

 of vanadic dioxide into vanadic pentoxide, since the ignition was con- 

 tinued with free access of air until the weight of the mass became con- 

 stant. The correction is of course to be added, so that we have for 

 the total loss 21.65 -f- 2.03 = 23.68 fj^. 



The analyses correspond tolerably well only with the formula 



5 V2O5 . 5 (NHJ.O + 41 aq, 



Calc'd. Found. 



33.44 \ 33.89 ^ (difF.) 



21.57 V- 76.50 21.21 V 76.32 

 21.49) 21.22) 



23.50 ^"'^^ I 23.68 



17.48 



6.12) 

 17.38) 



4247 100.00 



As the number of molecules of vanadic dioxide in this salt is uneven, 

 it will be necessary to double the formula in order to obtain a sym- 

 metrical structural scheme. 



ARSENIO-VANADICO- VANADATES. 



The salts of this series are formed with great ease by mixing solu- 

 tions of alkaline arsenates and vanadates, and adding a solution of 

 .vanadic dioxide in excess of chlorhydric acid. On evaporation large 

 very dark green crystals are deposited in abundance. In preparing 

 arsenio-vanadates it is difficult to avoid a partial reduction of the vana- 

 dic pentoxide by dust or other organic matter, and as a rule solutions 

 are obtained which contain both classes of salts. The arsenio-vanadico- 

 vanadates form a very beautiful and well-defined class of salts. 



Analytical 3fefhods. — Vanadic dioxide may be determined directly 

 by titrition with hypermanganate after addition of sulphuric acid and 

 appropriate dilution. To determine the arsenic present as arsenic 

 pentoxide, the arsenic is first to be brought into the form of arsenous 

 oxide by means of sulphurous acid after adding a little sulphuric acid to 

 the solution. The arsenic may then be precipitated as sulphide by 

 means of sulphydric acid, and weighed on a Gooch filter. The filtrate 

 contains all the vanadium in the form of dioxide, which may then be de- 

 termined by means of hypermanganate. The relation between the two 

 oxides of vanadium is then easily found. The accurate determination 



