OF ARTS AND SCIENCES. 67 



of the water of crystallization in these salts is difficult. They all lose 

 arsenic oxide when heated with sodic tungstate, and the only method 

 whicli can he safely eniploj^ed consists in heating weighed portions over 

 a radiating en}} of sheet-iron until a constant weight is obtained. 



12 : 12 : 6 Ammonium Salt. — When amnionic metavanadate or 

 divanadate is boiled with a large excess of ammonic arsenate, a color- 

 less solution is formed. On adding a solution of vanadic dioxide in 

 chlorhydric acid, a dark blue precipitate is formed, which dissolves 

 readily in an excess of dilute chlorhydric acid. No precipitate is formed 

 if the solution of the dioxide contains enough free acid. After stand- 

 ing some hours, a very dark green, almost black, crystalline salt is 

 deposited in quantity. This is to be washed with cold water. The 

 crystals exactly resemble those of the black potassic phospho-vanadico- 

 vanadate already described. They are insoluble in saline solutions, 

 and but slightly soluble in cold water. The solution has a greenish- 

 yellow color. It gives a brick-red indistinctly crystalline precipitate 

 with argentic nitrate, and a dull yellow flocky precipitate with mer- 

 curous nitrate. This last becomes crystalline on standing. It will 

 serve to prepare other salts of this series by double decomposition 

 with chlorides. The solution of the salt gives no precipitate with 

 cupric sulphate or baric chloride. In this salt, 



1.1623 gr. gave with KMnO^ 0.2199 gr. VOj = 18.91% 

 0.8719 gr. " " 0.3605 gr. V^O^ = 41.37% 



0.9726 gr. gave 0.5500 gr. AS0S3 = 52.87% 



0.8246 gr. " 0.4646 gr. '• = 52.68% 



1.0209 gr. *' 0.0538 gr. (NH/J2O = 5.27% 



The vanadic pentoxide, after deducting the equivalent of the dioxide 

 found, is 20.65%. The water could not be determined either by 

 heating with sodic tungstate or in a combustion tube, as arsenous oxide 

 sublimed in each case. It is therefore estimated by difference. 



The analyses agree fairly well with the formula 



12 As^O, . 12 VO, . 6 V2O. . 5 (NH,).0 + 7 aq, 



5242 100.00 



