COLL IN. 



oxalic and malic acids.* A quantity of artificial tannin is also 

 formed, and when the solution is evaporated to dry ness it de- 

 tonates. 



Muriatic acid dissolves glue with great ease. The solution is 

 of a hrown colour, and still continues strongly acid. It gra- 

 dually lets fall a white powder. This solution precipitates tan- 

 nin in great abundance from water ; and may be employed with 

 advantage to detect tannin when an alkali conceals it. 



Concentrated acetic acid softens and gradually dissolves col- 

 lin. The solution does not gelatinize, but the residue when 

 dried still retains the properties of collin. Dilute acids do not 

 prevent collin from gelatinizing on cooling, acetic acid does not 

 precipitate collin from its solutions. 



The fixed alkalies dissolve collin with facility, especially when 

 assisted by heat. Dilute alkaline solutions added to liquid col- 

 lin do not prevent it from gelatinizing. The earths, barytes, 

 strontian, lime, and magnesia have no sensible action on collin, 

 at least they occasion no precipitate. 



Collin combines with many salts. It dissolves a considerable 

 quantity of newly precipitated phosphate of lime. Alum does 

 not occasion a precipitate in solution of collin ; but if we add 

 an alkaline ley to the mixture, a copious precipitate falls, consist- 

 ing of collin combined with disulphate of alumina. The preci- 

 pitate resembles pure alumina : but if we heat it, we easily re- 

 cognize the presence of animal matter. Persulphate of iron does 

 not precipitate collin. But if we add to the persulphate enough 

 of ammonia to give it a deep red colour, and then mix it with 

 solution of collin, we obtain an abundant precipitate under the 

 form of a thick viscid, light-red clot. 



Neither acetate nor diacetate of lead nor sulphate of alumina 

 occasion any precipitate in solution of collin. 



If we mix by degrees solution of collin with that of corrosive 

 sublimate, a muddiness is produced which soon disappears. 

 This 'continues till we have added a certain quantity of the cor- 

 rosive sublimate. If we now add an additional quantity of this 

 reactive, the collin is thrown down under the form of a white clot, 

 which is coherent and very elastic. Similar precipitations are 

 obtained with nitrate of mercury and protochloride of tin. So- 

 lutions of silver and gold do not precipitate collin ; but when 



* Scheele*; Crell's Annals, ii. 17. English Trans. 



