On Chemical Tests. 



[Oct, 



113. STARCH, see 63. When solutions of starch and iodine are 

 added to each other, indigo-blue, reddish-blue, violet, or black, are the 

 colours that may be produced ; the colour depending on the quantities 

 and proportions of the two substances. 



a. Starch in solution is precipitated by subacefafe of lead; and if 

 boiled for a considerable time with sulphuric acid diluted with 12 parts 

 of water, sugar is formed. 



114. STEEL may be distinguished from iron thus: put on the arti- 

 cle to be examined a drop of dilute nitric acid, and let it remain one or 

 two minutes. If, on washing it off with water, a black spot is left, the 

 article examined is steel ; but iron if the spot be of a whitish grey 

 colour. 



115. STRONTIA, in a pure state resembles baryta in its properties, 

 It is detected by sulphuric acid which produces a white precipitate, in- 

 soluble in diluted free acids. Even a small quantity of strontian salt 

 produces a white precipitate with sulphuric acid ; but the precipitate 

 which does not form till after some time, is insoluble in diluted acid. 



a. Either oxalic acid, or binoxalate of potash, troubles neutral so- 

 lutions of strontian: if they are very dilute the opalescence does not 

 occur immediately. The precipitate is instantly augmented by the ad- 

 dition of caustic ammonia. 



b. Strontian salts may be distinguished from barytic salts by throw* 

 ing them into alcohol and setting fire to it. They occasion a carmine 

 red flame, particularly when stirred, and when the alcohol is nearly 

 burnt away : baryta does not produce this coloured flame, see g. 



c. Neutral succinate of ammonia produces an immediate precipitate 

 in concentrated solutions of barytes; but none in concentrated neutral 

 solutions of strontia, at least not until after some time. This test there- 

 fore distinguishes baryta from strontia. 



d. M. Liebeg states that the iodate of soda is an excellent re-agent 

 for separating barytes from strontia; the latter is not at all precipitated 

 by it, while the former is completely thrown down in neutral solutions. 

 The precipitate is flaky. 



e. For discriminating strontia from lime, &C.,. see 72, and 79 d, from 

 barytes, see 40 d, from lithia see, g in this article. 



/. Hydro-fluo-silicic acid, hydrosulphuret of ammonia, prussiate of 

 potash, and red prussiate of potash produce no precipitate in solutions 

 of stronia. 



g. Salts of strontia impart to the flame of the blow-pipe a bright 

 carmine red colour, when fused on the platinum wire. Lithia does the 



