308 SOLID PARTS OF ANIMALS,,' 



Nitric acid changes the blue colour to yellow, and ammonia to 

 orange. 



The caustic fixed alkalies dissolve horn easily ; but ammonia 

 does not attack it 



If, after freeing horn from fat by means of alcohol, we place 

 it in contact with very dilute caustic potash, the liquid acquires 

 a disagreeable smell, and the horn assumes the form of a jelly, 

 and gradually dissolves. The liquid is pale-yellow, and can 

 hardly be filtered. When a concentrated solution of caustic po- 

 tash is poured upon raspings of horn a very disagreeable smell 

 is evolved, and the raspings gradually soften into a matter like 

 glue, grey-coloured and semitransparent. The alkaline liquid 

 has a deep-yellow colour, and gives traces of ammonia. The 

 viscid mass is a combination of the horn with the potash. It is 

 insoluble in the concentrated alkaline liquor while cold ; but dis- 

 solves in it when assisted by heat. We pour the alkaline ley 

 from the viscid mass, and wash it with cold water. Thus treated, 

 it dissolves in water without communicating any colour. The 

 solution has an alkaline reaction. When acetic acid is poured 

 into it in such quantity as not to decompose it completely, a 

 white curdy precipitate falls, which soon collects into a viscid 

 gluey mass. It is a compound of horn with a minimum of al- 

 kali. If we decant off the saline solution which floats over it, 

 and then pour water on it, it gradually gelatinizes, and at last 

 dissolves into a mucilage decomposable by acids. If, on the 

 contrary, we add enough of acetic acid to decompose the whole 

 compound of horn and potash, and to leave a surplus of acid in 

 the liquid, a precipitate falls quite similar to the former in ap- 

 pearance, but which is a compound of horn and acetic acid. It 

 is insoluble in water, whether cold or hot, and also in alcohol. 

 But it is soluble in acetic acid, Prussiate of potash throws down 

 from this solution semitransparent flocks, which subside very 

 slowly to the bottom of the vessel. Carbonate of ammonia gives 

 a precipitate soluble in a great excess of the reagent. Corrosive 

 sublimate, acetate of lead, persulphate of iron and tannin, throw 

 down abundant precipitates. 



If we evaporate the acetic acid solution to dryness, we obtain 

 a yellow, transparent, hard, and viscid mass, which is insoluble in 

 water. When we evaporate to dryness the solution precipitated 

 by acetic acid, and digest the residue in water, a portion of horn 



