66 Royal Society : — 



Calculated. Found. 



Na 3 == 69'0 14-6 13-8 



V .....= 51-3 10-86 10-86 



4 = 64-0 13-56 



16H o =288-0 6097 60*44 



472-3 99-99 



The sodium in this and in the following compounds was separated 

 from the vanadium by precipitating the vanadic acid as the perfectly- 

 insoluble basic lead salt hereafter described. This was dried at 100° 

 and weighed, then dissolved in nitric acid and decomposed by sul- 

 phuric acid, and the solution of V 2 5 in excess of this acid gave on 

 evaporation a finely crystalline mass. The filtrate from the lead pre- 

 cipitate freed from lead yielded on evaporation sodium sulphate. Full 

 analytical details of this method, as well as of the other by precipi- 

 tation as the insoluble ammonium metavanadate, are given in the 

 memoir. By frequent crystallizations the trisodium vanadate is slowly 

 decomposed into the tetrasodium salt, caustic soda being formed. 

 This singular reaction was most carefully examined and the amount 

 of sodium hydroxide liberated determined volumetrically. 



2. Tetrasodium Vanadate, Na 4 V 2 7 + 18H 2 O. — This salt crystal- 

 lizes in beautiful six-sided tables ; it is easily soluble in water, inso- 

 luble in alcohol, and is precipitated by the latter liquid from aqueous 

 solution in white scales of a silky lustre. As long as the salt contains 

 free alkali or tribasic salt, it forms, on precipitation with alcohol, oily 

 drops which solidify after some time. The tetrasodium vanadate is 

 always formed by the first fusion of vanadic acid with excess of car- 

 bonate of soda, and can be easily prepared in the pure state by re- 

 crystallization. 



Found (mean of many 

 Calculated. determinations). 



Na 4 = 92-0 14-58 14-61 



V 2 = 102-6 16-27 15-97 



7 = 112-0 17-27 



18H 2 ....= 324-0 51-38 51-80 



630-6 99-99 



The salt loses 17 molecules of water at 100°. 



The corresponding Calcium and Barium Vanadates, Ca 2 V 2 7 , 

 and Ba 2 V 2 7 , are white precipitates obtained by adding the chlo- 

 rides to a solution of tetrasodium vanadate. If calcium chloride be 

 added to a solution of the trisodium salt, dicalcium vanadate is pre- 

 cipitated, the solution becoming strongly alkaline from formation of 

 calcium hydroxide and absorbing carbonic acid from the air. Com- 

 plete analysis showed that the calcium salt contains 1\ molecules 

 of water of crystallization, whilst the barium salt is anhydrous. 



head Vanadates. 



1. Trihasic or Ortho-Lead Vanadate, Pb ; ,2(V0 1 ). — Obtained as 



