Intelligence and Miscellmieous Articles. 149 



detecting 1 -90,000dth of protoxide of iron, wbile tlie latter does not 

 detect less than l-1800dth of the protoxide. The red ferrocyanate of 

 potash is soluble in twice its weight of cold water, and less than its 

 own weight of boiling water. It is insoluble in alcohol, does not act 

 upon litmus, but renders syrup of violets green. The concentrated 

 solution in large quantity is almost black, its colour being so ex- 

 tremely deep, but in small portions it is transparent and of a greenish 

 red colour. A very small quantity renders a considerable portion of 

 water green. In the formation of this salt half of the acid of the fer- 

 rocyanate is destroyed by the chlorine, and the alkali of this is com- 

 bined with muriatic acid. The ferrocyanates of soda, ammonia, ba- 

 rytes and lime, are all converted into red ferrocyanates by chlorine. 



The red ferrocyanate of potash precipitates tin white ; silver and 

 zinc of an orange colour ; nickel, bismuth and titanium brown ; copper 

 of a dirty brown ; cobalt and uranium different shades of reddish 

 brown 5 both oxides of mercury brown. Lead is not precipitated; but 

 after some time reddish-brown crystals are deposited, which when de- 

 composed by sulphuric acid, separate perferrocyanic acid, which cry- 

 stallizes in needles, reddens litmus paper, and has at first an acid 

 and afterwards a styptic taste. When slightly heated it separates 

 into hydrocyanic acid and Prussian hXnQ.— Hensmari's Repertoire de 

 Chimie, Aug. 1828. 



ON GALLIC ACID, TANNIN, AND A PECULIAR PRINCIPLE IN 

 COFFEE. 

 M. Pfaff states the following as the results of the experiments 

 which he has made on the above-named substances : 



That tannin ought to be considered as an immediate principle of 

 the vegetable kingdom, and not as composed of gallic acid or any 

 other acid, and a peculiar vegetable body. 



That the character which especially distinguishes tannin from gallic 

 acid, is its action with solution of isinglass, a weak solution of gold, 

 a solution of titanium, tartar emetic, the alkaline carbonates, and the 

 salts of the vegetable alkalies. Gallic acid reduces gold perfectly, 

 tannin merely reduces it to the state of a hydrate of the purple sub- 

 oxide ; tincture of galls acts like tannin. Solution of titanium pre- 

 cipitates tannin and tincture of galls of an orange colour similar to 

 the golden sulphur of antimony ; whilst by gallic acid the same solu- 

 tion is merely rendered opalescent, and of a yellow colour. In the 

 solution of tartar emetic, gallic acid occasions immediately a white 

 precipitate J the solution of tannin renders it only slightly turbid, 

 and does not colour it for a considerable time. 



The alkaline carbonates render gallic acid brown, which by the 

 gradual action of the air changes to green ; they precipitate tannin 

 abundantly, and the supernatant liquid is brown, but it becomes very 

 slowly of a dirty green. The acetates of mor|)hia and strychnia, and 

 the sulphates of quina and cinchonia, do not precipitate gallic acid, 

 but they i)recipitate tannin very readily. 



Gallic acid has a very marked action upon ammonia and the fixed 

 alkaline carbonates. The smallest particle of carbonate of soda ex- 

 isting 



