486 APPENDIX. 



the tetrahedric crystals, and a dark pomegranate-red colour in the 

 case of the prismatic crystals ; the solution of the tetrahedric crystals 

 separates into a brownish coagulum when heated to 63 ; that of 

 the prismatic crystals when heated to 64 or 65. Small quantities 

 of spirit produce no alteration in the aqueous solution, but when a 

 larger quantity is added, a flocculent precipitate is formed, which is 

 again soluble in water ; a very large quantity of spirit or absolute 

 alcohol precipitates the substance in clots, which are insoluble in 

 water. When a little spirit is added to the aqueous solution, the 

 substance coagulates at a lower temperature than in the pure watery 

 solution. Ether does not produce any turbidity in the aqueous 

 solution. 



Cold concentrated nitric acid renders the crystals dark and 

 almost black. On being heated, however, they become yellow and 

 dissolve with tolerable readiness into a yellow fluid. The aqueous 

 solution of the crystals yields a light brownish flocculent precipitate, 

 even when very much diluted. 



Hydrochloric and sulphuric acids do not give rise to any pre- 

 cipitates from the watery solution of the tetrahedric crystals, 

 although they precipitate the solution of the prismatic crystals ; 

 this difference depends, however, solely upon the different concen- 

 tration of the solutions ; for if the solution of the prismatic crystals 

 be diluted, as for instance, by the addition of four times its volume 

 of water, no precipitate will be formed either with hydrochloric or 

 sulphuric acid ; but if, on the other hand, from four to six times 

 the volume of concentrated hydrochloric acid, or an equal volume 

 of English sulphuric acid be added to a solution of the tetrahedric 

 crystals, this substance will likewise be precipitated. 



The crystalligable substance is easily soluble in acetic acid, 

 which simply changes the colour of the red watery solution into a 

 brownish-yellow. If we neutralise with ammonia the fluid which 

 has been acidified with acetic acid, pale brownish flakes are sepa- 

 rated. Like other protein-bodies, the crystalline substance may 

 be precipitated from the acid solution by yellow as well as by red 

 prussiate of potash. It has also the further property in common 

 with them, of being precipitated by neutral alkaline salts from the 

 acetic-acid solution, or by acetic acid from the solution which has 

 been treated with such salts. This precipitate which is thus 

 obtained, is soluble in water, and exhibits very different properties 

 from the original crystalline substance, a point to which we shall 

 revert at a future page. 



The crystals are insoluble in a concentrated solution of potash ; 



