OP ARTS AND SCIENCES. 137 



white' indistinctly crystalline mass. This was redissolved and potassic 

 bromide added in excess, when an abundant white crystalline fine-grained 

 precipitate was thrown down, which was drained on the filter-pump, 

 and then washed with cold water. This was dissolved in much boil- 

 ing water, and argentic nitrate added, when a white crystalline salt was 

 thrown down mixed with brownish-red crystals of argentic arsenate. 

 The mass was treated with very dilute nitric acid, which readily dis- 

 solved the arsenate, the undissolved portion appearing under a lens as 

 made up of opaque white acicular crystals. These were well drained, 

 washed with cold water, and dried on paper by pressure, when the 

 mass showed a faint yellowish tint. The salt is but slightly soluble 

 in cold water. Of this salt, — 



0.7488 gr. gave 0.5024 gr. W0 3 = 67.09% 



0.7531 gr. " 0.5067 gr. " = 67.29% 



2.0321 gr. " 0.6147 gr. AgCl = 24.45% Ag 2 



1.0215 gr. « 0.3096 gr. " = 24.48% " 



0.9209 gr. lost on ignition 0.0340 gr. water = 3.69% 



The analyses correspond tolerably well to the formula 

 16 W0 3 . As 2 O s . 6 Ag,0 -4- 11 aq, 

 which requires : — 



Calc'd. 



16 W0 3 3712 67.10 67.09 67.29 



As 2 6 5 230 4.16 4.65 (diff.) 



6 Ag 2 1392 25.16 24.45 24.48 



11 H 2 198 3.58 3.69 



5532 100.00 



I do not place implicit confidence in the formula given, as the two 

 determinations of argentic oxide are too low. It is very possible that 

 the salt was slightly decomposed by the dilute nitric acid employed to 

 remove the arsenate. But in any case it is proved that arsenio-tung- 

 states exist in which the ratio of W0 8 to As 2 5 is higher than 6:1, 

 and a method of obtaining such compounds is pointed out. 



General Conclusions. — The general results of my investigation of 

 the phospho-tungstates may be stated briefly as follows : — 



1. The phospho-tungstates form a series of which the lowest term 

 probably contains six atoms of tungstic to one of phosphoric oxide, and 

 the highest, twenty-four atoms of tungstic to one of phosphoric oxide. 



2. At least the greater number of phospho-tungstates contain an 

 even number of atoms of tungstic oxide. The homologizing term for 

 these cases is therefore 2 WO,, 



