OP ARTS AND SCIENCES. 13 



Marignac found in this salt five molecules of water. Lotz and 

 Scheibler gave it the formula 



7 W0 3 . 3 (NH 4 ) 2 + 3 H 2 0. 



Marignac has also described and analyzed an ammonium salt to 

 which he gives the formula 



5 W0 3 . 2 (NH 4 ) 2 + 5 H 2 0. 

 I should double this formula, and write it 



10 W0 3 . 4 (NH 4 )0 + 10 H 2 0, 



so that it would then belong to the series of 10:4 salts, the existence of 

 which I have endeavored to establish. According to Marignac, it 

 breaks up by solution in water into the 12:5 and 8 : 3 salts. 



2{10 W0 3 . 4(NH 4 ) 2 0} = 12 WO, . 5(NH 4 ) 2 -f 8 W0 3 . 3(NH 4 ) 2 0. 



Zinc Salts. — When a solution of zincous sulphate is added in small 

 excess to a hot solution of the 10: 4 sodic tungstate, no precipitate is 

 produced at first, but after a few seconds beautiful aggregates of white 

 needles make their appearance, and continue to be deposited for some 

 time. They are almost perfectly insoluble in boiling water. For 

 analysis they were washed with cold water and dried in pleno over 

 sulphuric acid. The zinc salt is soluble both in an excess of zincous 

 sulphate and of sodic tungstate ; hence the precipitate which is at first 

 formed is instantly redissolved and does not become permanent until a 

 small excess of the sulphate is added. In this salt, 



0.3342 gr. lost on ignition 0.0349 gr. water = 10.44% 

 0.6392 gr. gave 0.5128 gr. W0 3 = 80.50% 



1.0205 gr. " . 0.8200 gr. " =80.35% 



These analyses correspond with the formula 

 6W0 8 . 2ZnO + 10 aq. 



From this it appears that the zinc salt is formed by the decomposi- 

 tion of the 10 : 4 sodic tungstate. The result may be expressed by the 

 equation, 



