HORNS, NAILS, AND SCALES. 309 



remains, but the liquid contains a little, which behaves with re- 

 agents in the same way as the acid solution. 



When, instead of acetic acid, we employ muriatic acid to throw 

 down horn from potash, the precipitate obtained is more abun- 

 dant, because it is less soluble in the excess of muriatic acid ad- 

 ded. This precipitate constitutes a coherent mass ; but if we 

 wash it and then digest it in water, it dissolves and produces a 

 milky liquor, which, by the addition of an additional quantity of 

 acid, produces a viscid and acid precipitate. 



Berzelius considers horn as a modification of fibrin. He founds 

 his opinions on the circumstances, that its acid solution is preci- 

 pitated by prussiate of potash ; that horn remains dissolved in 

 acetic acid ; and that its neutral combination with muriatic acid, 

 which is partially soluble in water, coagulates anew when an ad- 

 ditional quantity of muriatic acid is added. 



If we boil horn with a concentrated solution of potash, it sof- 

 tens and then dissolves, while abundance of ammonia is given 

 out, which has a very disagreeable smell. This disengagement 

 continues for a long time. The portion of horn not dissolved is 

 softened, and it becomes so slippery that, if we take it out of the 

 liquid, we can scarcely hold it in our fingers. If we wash it in 

 cold water to remove the alkali it dissolves in the liquid with- 

 out communicating to it any colour. 



The solution of horn in boiling potash is thick, of a dark- 

 brown colour, and similar to a bad potash soap. It dissolves 

 easily in water, forming a muddy solution, which, when filtered, 

 is pale yellow, leaving a minute quantity of deep-green powder, 

 which Berzelius considers as sulphuret of iron. Its dark colour 

 vanishes when the powder is exposed to the air. If we mix the 

 alkaline liquor with an acid, carbonic acid is disengaged mixed 

 with sulphuretted hydrogen gas. If the acid added be muria- 

 tic, after the carbonic acid is disengaged, a compound of the acid 

 and horn, the same as described above, falls down ; but in small 

 quantity compared to that of the horn acted upon. If we digest the 

 acid liquor from which this precipitate has fallen over carbonate of 

 lime till it is neutralized, and then evaporate the whole todryness, 

 and digest the dry residue in alcohol, to dissolve the chloride of 

 calcium, a matter remains which dissolves readily in water, to which 

 it communicates a pale-yellow colour. When this solution is 

 evaporated to dryness it leaves a hard transparent matter, which 



