Chemical Science. 211 



water, and neutralized by carbonate of potash, will furnish a larp^e 

 quantity of the potash salt. All the potash salt obtained in thes6 

 operations is to be re-dissolved in boiling water, and nitric, muriatic, 

 or sulphuric acid added ; as the solution cools, the peculiar sub- 

 stance will be observed to form very brilliant plates of a clear yellow 

 colour, generally in equilateral triangular forms. 



Sometimes crystals are not formed after the action of the nitric 

 acid on the indigo, in which case the liquor must be evaporated, 

 and water added, when the substance will precipitate, and must be 

 purified as already described. Four parts of indigo yield one of the 

 pure substance. 



When the substance is heated, it fuses, and is volatilized without 

 decomposition ; when subjected to a sudden strong heat, it inflames 

 without explosion, its vapours burning with a yellow flame, and a 

 carbonaceous residue remaining. It is but little soluble in cold 

 water, but much more in boiling water ; the solution has a bright 

 yellow colour, reddens litmus, has an extremely bitter taste, and 

 acts like a strong acid on metallic oxides, dissolving them, and form- 

 ing peculiar crystallizable salts. — Ether and alcohol dissolve the 

 substance readily. 



When fused in chlorine or with iodine, it is not decomposed, nor 

 does solution of chlorine affect it. Cold sulphuric acid has no 

 action on it ; when hot, it dissolves it, but water separates the sub- 

 stance without alteration. Boiling muriatic acid does not affect it, 

 and nitro-muriatic acid only with great difficulty. 



These results show that no nitric acid is present in the substance^ 

 and other experiments prove that no oxide of nitrogen exists in it ; 

 it contains no oxalic or other organic acid, for when its salt is boiled 

 with chloride of gold, the latter is not reduced. 



When heated to redness with oxide of copper, it gave a mixture 

 of nitrogen and carbonic acid, in the exact proportion of 1 volume 

 of the former, to 5 of the latter. This was a constant result, and 

 in no case was any sulphuric or muriatic acid left in the copper. 

 0.0625 grammes of the substance thus decomposed, gave 45 cubic 

 centimeters of the mixed gases, estimated at 0°C. (32° F.) and the 

 pressure of 28 inches of mercury, according to which the acid would 

 be composed of carbon 32.392 ; nitrogen 15.2144 ; oxygen 52.3936 

 per cent. From the mean of several experiments, it appeared that 

 the following might represent the composition correctly. — 



12^ atoms of carbon ... 93.75 or 31.5128 



2| „ azote . . . .43.75 „ 14.7060 



16 „ oxygen . . .160.00 „ 53.7812 



297.5 100. 



100 parts of the acid neutralize a quantity of base equivalent to 

 3.26 of oxygen, which is to the oxygen of the acid, as 1 : 16 ; the 

 equivalent number of the acid derived from the analysis of the 



P 2 



