OF ARTS AND SCIENCES. 121 



The analyses correspond to the formula 



24 W0 3 . P 2 5 . 3 K 2 . 3 H 2 + 14 aq. 



,18 



5.17 



6299 100.00 100.00 



24 : 3 Acid Ammonium Salt. — When a solution of a salt of am- 

 monium is mixed with one of sodic tungstate and phosphate, no precipi- 

 tate is formed, even after standing ; but if a large excess of chlorhydric 

 or nitric acid is poured in, a white or very pale yellowish heavy crys- 

 talline salt is thrown down in large quantity. This salt is an acid 

 phospho-tungstate of ammonia, the constitution of which varies with 

 the proportions of the salts employed in its preparation and with the 

 conditions of the experiment. 



The different salts, however, resemble each other very closely, and 

 may be described in the same terms. They are either perfectly white 

 or have in mass a faint tinge of yellow and an extremely fine-grained 

 crystalline structure. They are very slightly soluble even in hot 

 water, and give milky emulsions which settle very slowly. Like many 

 other phospho-tungstates and tungstates, they are difficult to wash, as 

 they pass through the closest filter-paper with extraordinary facility. 

 This difficulty may, however, be overcome by adding ammonic nitrate 

 to the wash-water. The acid phospho-tungstates of ammonium are 

 soluble in ammonia-water, but the crystals obtained from such solutions 

 are either ammonic tungstates or salts of series different from that to 

 which the salt dissolved belonged. They are readily decomposed by 

 a red heat, leaving a mixture of tungstic and phosphoric oxides. 

 When boiled with mercurous nitrate, they yield mercurous salts and 

 ammonic nitrate. 



In one preparation in which sodic tungstate and phosphate were 

 mixed in the proportion of 20 atoms of the former to 2 of the 

 latter, ammonic nitrate was added, and afterward nitric acid. The 

 precipitate was washed with solution of ammonic nitrate, and after- 

 ward with alcohol and water, and dried by pressure with woollen paper. 

 Of this salt, — 



