1819.] some new Combinations of Prussic Acid. 441 



diately repeated the experiment in such a way as to remove all 

 suspicion of the presence of iron. I took 10 gr. of fine starch 

 which 1 mixed with an ounce of the water of the Neva. I added 

 20 or. of prussiate of potash, and boiled the whole in a matrass. 

 The'liquid became transparent, and remained colourless during 

 the whole time of boiling. I then added muriatic acid, which 

 made it immediately assume a green colour as if I had poured 

 into it a solution of 'iron. The precipitate in 48 hours became of 

 a fine deep blue. I repeated the experiment with different 

 starchy substances, as arrow root, sago, potato starch, and 

 always obtained the same result. Thus starchy bodies, when 

 dissolved in water at the temperature of 212°, have the property 

 of forming blue prussiates like iron. 



II. Prussiate of Gum Arabic. 



I made the same trials with some analogous substances. Ten 

 grains of gum, arabic and 20 gr. of prussiate of potash were dissolved 

 and heated together in a matrass with an ounce of water. The 

 mixture remained transparent and colourless during the boiling, 

 foiling muriatic acid made it pass to a deep green. The preci- 

 pitate was abundant, and fell down rapidly. 



The prussiate of gum is less black than pure prussiate of iron. 

 It is insoluble in water, and in muriatic acid. Concentrated 

 sulphuric acid dissolves it, and destroys the colour ; but it appears 

 again when the solution is diluted with water. The prussiate in 

 tliat case precipitates with all its lustre, and when it is washed 

 and dried, we cannot from its colour distinguish it from common 

 prussian blue. 



III. Prussiate of Sugar. 



The same process and the same quantities being employed 

 with sugar yielded likewise a blue prussiate, which was at first 

 green, and which, when exposed to the air, assumed a lighter 

 shade than the preceding blues. . 



To avoid useless repetitions, I shall merely say, that havmg 

 experimented in the same way with solutions of gelatin, of 

 cochineal, of tannin, of soap, and even of white wax melted and 

 mixed with the prussiate of potash, on decomposing the prussiate 

 by muriatic acid while boiling-hot, I always obtained blue prus- 

 siates ; while none of these compounds could be formed at the 

 temperature of the atmosphere.* 



Of all these substances cochineal is the one which resists most 

 the action of prussic acid, the combination not taking place till 

 after half an hour's boiling. This colouring matter, which the 

 mineral acids and alkalies do not decompose, becomes green by 

 "its union with prussic acid. The precipitate resembles the juice 



• It may be thought that those substances are coloured by the iron of the prnssir 

 arid as by a tincture ; but the gum and starch become insoluble in water, which 

 indicate* u true combination, and the cochineal becomes gieeu, and not violet. 



2t 



