S54 



Its properties 

 when pure. 



Action of heat 

 on it. 



ApparatvTS for 

 examining its 

 ..products. 



Heat applied. 



Gaseous pro- 

 ducts. 



Carbonic and 

 prussic acids. 



Mode of detect 

 ing the latter. 



ACTION OP NITRIC ACID ON INDIGO. 



When the amer is very pure, it is white inclining fo 

 straw-colour. Its solution in water is not reddened by 

 salts of iron at a niaxinxutn. That which was employed in 

 the following experiments had been boiled in nitric acid: 

 afterward crystalized repeatedly; combined with potash, 

 and then separated from it by muriatic acid; and lastly 

 crystallized, till, when redissohed in water, it no longer 

 precipitated solution of silver. 



16. The amer, being gently heated in a common phial, 

 sublimed in little needles, or scales, of a white colour in- 

 clining to straw-yellow. Thrown on a redhot iron it took 

 fire, and left a coal, which melted. If exposed to a red 

 heat in a retort, a pretty strong smell of nitrous acid and 

 of prussic acid is evolved. 



To examine the products of the amer subjected to the 

 action of heat, I contrived an apparatus consisting of a 

 glass ball surmounted with a tube, which terminated under 

 ajar filled with mercury. Into the ball 1 introduced 2 dec. 

 [S grs.] of amcr, more would have burst it, and fastened 

 the tube to the jar by means of a wire. 



17. When the apparatus was thus arranged, I heated the 

 ball with a redhot coal : the amer melted, grew black, and 

 took fire ; a light coal remained ; and aqueous vapour, gas, 

 and a little charcoal passed into the receiver. 



The gaseous product reddened litmus paper. It had the 

 smell of nitrous acid, mixed with tliat of prussic; and I 

 anal3'sed it in the following mode. I first passed some 

 water into the jar, and a slight absorption took place. 

 When this appeared to be at an end, I shifted the water to 

 another jar filled with mercury; and found, that it had 

 dissolved a portion of amer, which had been volatilized 

 without decomposition, some carbonic acid, and some 

 . prussic acid. To detect ih•r^ latter it was necessary, to sa- 

 turate the liquid with car.bonate of potash ; and pour it 

 into a small glass retor/. adapted to a receiver, in which 

 were some threads twisted together, impregnated with greea 

 sulphate of iron, an(?. afterward dipped in a weak solu- 

 tion of potash. On distilling, water and prussic acid 

 passed over ; and the thread, after having been washed with 

 weak muriatic apid, became bluci (If sulphate of iroa 



were 



