SILK. 343 



ceding chapter of this volume. It differs so much, both in its 

 properties and composition fromjSfanv from blood, that it would 

 be better to distinguish it by a particular name. 



2. The substance from silk which Mulder calls gelatin is brit- 

 tle, slightly yellowish, and translucent. It has neither taste nor 

 smell, is not altered by exposure to the air, and is specifically 

 heavier than water. When heated it swells up, catches fire, 

 burns with flame, and leaves a bulky charcoal. When this char- 

 coal is burnt, it leaves a white residue, consisting chiefly of car- 

 bonate of soda. In water it is completely soluble, but it is inso- 

 luble in alcohol, ether, fixed and volatile oils. The aqueous so- 

 lution is very glutinous, and speedily undergoes decomposition, 

 giving out an ammoniacal smell. 



It is soluble in concentrated sulphuric acid at the common tem- 

 perature of the atmosphere, without undergoing any change of 

 colour. When heated, the solution blackens and gives out an 

 odour of caromel and sulphurous acid. In dilute sulphuric acid, 

 it dissolves when assisted by heat. If we boil the solution, satu- 

 rate the acid with chalk, filter and evaporate and digest the resi- 

 due in alcohol, that liquid, on cooling, deposites a quantity of 

 sugar. 



Concentrated nitric acid dissolves the gelatin of silk at the or- 

 dinary temperature of the atmosphere. When heat is applied, 

 nitrous gas escapes, and oxalic acid is formed, 



It dissolves in concentrated muriatic acid without change of 

 colour. Both common and pyrophosphoric acids dissolve it. The 

 solution in concentrated acetic acid, when evaporated, leaves a 

 thick liquid matter, from which water precipitates nothing, but 

 prussiate of potash throws down a beautiful green precipitate, 

 which is soluble in water. 



It is soluble in potash, soda, and ammonia, but is precipitated 

 again by acids. If we add these alkalies to an acid solution, a 

 precipitate falls which is redissolved if we add an excess of the 

 alkali. It is soluble by boiling in carbonate of potash. 



The aqueous solution being evaporated to the requisite con- 

 sistence, becomes gelatinous and adhesive. The aqueous solu- 

 tion is precipitated white by alcohol, infusion of nut-galls, nitrate 

 of mercury, diacetate of lead, chloride of tin, chlorine and bro- 

 mine. The chloride of gold throws down a yellow precipitate. 



It is not precipitated by oxalic acid, acetate of lead, corrosive 



