98 Mr. Crum on Indigo. [Feb. 



ing the proportion of muriate of ammonia necessary to prevent 

 the substance from dissolving in it, and filter again. Dissolve 

 anew the precipitate in a large quantity of distilled water ; heat 

 the solution to drive off any particles of air which might prevent 

 the impurities from subsiding, and let it stand two or three days 

 in a tall vessel. Then draw off with a syphon as much as may 

 be thought perfectly clear, leaving the remainder to be washed 

 with more distilled water. Add to the solution any alkaline salt, 

 till the substance be precipitated ; then throw it upon a filter, 

 and wash with distilled water till the liquid refuses to pass 

 through. 



The colour of the substance thus prepared is not much inferior 

 in beauty to that prepared by the former process. Dried and 

 burnt to ashes, a considerable quantity of earthy matter is always 

 left, but very little of the alkaline salt that precipitated it. Its 

 solution is always more or less purple, particularly if it be some- 

 what strong. In alcohol, it is completely blue, and the aqueous 

 solution becomes blue when it is heated. After being dried, it 

 does not dissolve in water. 



When a solution of phenicin is precipitated, the liquid that 

 remains is always more or less coloured with cerulin ; and how- 

 ever often this be repeated upon the same material, a little ceru- 

 lin is always left. If it has been heated, more cerulin is formed. 

 It follows from this, that phenicin is changed into cerulin by the 

 action of water alone. 



Phenicin dissolves in the water of liquid ammonia without 

 injury ; but the fixed alkalies destroy it, though not very readily. 

 Chloride of tin precipitates the solution, but gradually redissolves 

 the precipitate, forming a yellow solution ; and the phenicin is 

 thrown down again of its own colour, by the salts of copper. 



Phenicin dissolves readily in concentrated sulphuric acid, 

 forming a blue solution; and if this be poured immediately into 

 water, the greater part of it is precipitated again, the impurities 

 of the acid being sufficient to prevent its solution in water. A 

 portion is converted into cerulin, which remains in solution. 

 When allowed to remain dissolved in sulphuric acid, it is soon 

 entirely converted into cerulin ; consequently in preparing 

 phenicin by the second process, it is impossible to prevent the 

 formation of a certain portion of cerulin. 



Constitution of Phenicin. 



The facts which I have stated to prove that cerulin differs 

 from indigo only in containing more or less water, equally apply 

 to this substance. 



The perfect insolubility of phenicin in weak saline solutions ena- 

 bles us to determine pretty nearly how much of it a quantity of 

 indigo is capable of producing. Ten grains of sublimed indigo 

 were put into a small phial with 300 grains of sulphuric acid ; 



