108 Progress of Foreign Science. 



He then transferred the precipitate into a phial along with hydro- 

 sulphuret of ammonia, corked it up, and left the substances for 

 some time in digestion. The iron was thereby converted into a 

 sulphnret, which was removed by digestion in muriatic acid, while 

 the greater part of the oxide of titanium remained in a pure state. 

 Oxide of titanium thus prepared has a fine white colour. When 

 ignited, it assumes a lemon-yellow hue, which on cooling passes 

 back into white. If this ignited oxide be laid on blue litmus paper, 

 and moistened with water, the water becomes reddish, but the 

 paper remains unchanged. But when finely triturated oxide is 

 sprinkled on tincture of litmus covering white paper, the licpiid is 

 immediately reddened. It combines with alkalis, forming salts, 

 which are for the most part with excess of acid. The super- 

 titanate of soda is composed as follows : 



Titanic acid . . . 74.73 



Water .... 10.13 



Soda 15.14 



100.00 

 The dry salt consists of about 83 parts of acid and 17 of soda in 100. 

 When a solution of red oxide of iron in an acid is mixed with 

 tartaric acid, it is known that the oxide can be precipitated neither 

 by caustic alkalis, nor by their carbonates or succinates ; but tinc- 

 ture of galls, triple prussiate of potash, and alkaline hydrosul- 

 phurcts, shew the presence of iron in such a solution. Mr. Rose 

 hence conceived, that if the muriatic solution of the titanium oxide 

 fused with alkali, were mixed with tartaric acid, he might obtain, 

 by precipitation with ammonia, that oxide entirely free from iron. 

 But he found that tartaric acid imparted to the solutions of many 

 other oxides, the property " of not being thrown down by caustic 

 alkalis or their carbonates, though they were otherwise precipitable 

 by them. Among these oxides, that of titanium ranks ; for when 

 its solution contains tartaric acid, it cannot be thrown down by 

 carbonate of potash, or by carbonated cr pure ammonia. The 

 presence of alumina in a solution cannot be detected by re-agents, 

 when this contains tartaric acid, which in like manner prevents 

 the coloured aluminous lakes from being precipitated. Moreover, 

 the oxides of manganese, of cerium, yttrium, cobalt, nickel, and 

 magnesium, are in the same predicament. Solution of proto- 

 sulphate of iron with tartaric acid is merely rendered intensely 

 green by ammonia, and changes, after long standing in the air, 

 to a yellow-coloured solution which contains iron. The oxide of 

 lead likewise is not separable by alkalis, when its solution has 

 been treated with so much nitric acid, that no tartrate of lead can 

 precipitate. Oxides of tin and copper fall under the same head. 

 The solution of the latter mixed with tartaric acid becomes, on 

 the addition of carbonate of potash, merely of the same sky-blue 



