118 PROCEEDINGS OF THE AMERICAN ACADEMY 



Analyses I. and II. were made with two different preparations of 

 the colorless crystals ; III. and IV. were made with the sulphur-yellow 

 salt. The determinations of (W0 3 -\- P 2 0.) in I., II., aud III. were 

 made by the evaporation process without the use of mercuric oxide, 

 but in IV. the oxide was employed. As a check upon the quantity 

 of sodic oxide two direct determinations were made in III. the oxide 

 being weighed as nitrate. In this manner, 



1.3273 gr. gave 0.0875 gr. N0 3 Na = 2.40% 

 1.2593 gr. " 0.0924 gr. " = 2.68% Na 2 



The mean of these two is 2.54%. As the phosphoric oxide in the 

 analyses above cited was determined from a single precipitation as 

 ammonio-magnesian phosphate, I have, as usual in such cases, applied 

 a correction of 0.15% to the mean. These analyses lead to the 

 formula 



24 W0 3 . P 2 5 . 2 Na 2 . 4 H 2 -f 23 aq, 

 or, 



W 24 P 2 71 (NaO) 4 (HO) 8 + 23 aq. 



The mean of the five determinations of (WO, -f- P 2 0.) is 90.20. 

 The formula requires 90.35. There can, I think, be no reasonable 

 doubt as to the constitution of the acid sodium salt, though it is difficult 

 to obtain it in a state of absolute purity. The salt is very conveniently 

 prepared, however, and makes an excellent reagent for alkaloids. 

 For this special purpose it is best to mix the normal tungstate and 

 hydrodisodic phosphate in the proportion of 24 atoms of the former to 

 3 or 4 of the latter, boil the mixed solutions for a short time, filter, and 

 add chlorhydric acid in excess, but in small successive portions. A 

 precipitate is usually formed on each addition of acid which disappears 

 on stirring the liquid. On standing, a mass of crystals of the acid suit 

 separates. This should be drained, washed with a little cold water, 

 then dissolved in cold water for a reagent, the clear liquid only being 

 used. 



The 24 : 2 acid phospho-tungstate of sodium appears to be always 

 formed when an excess of chlorhydric or nitric acid is added to a so- 



