1823.] Mr. Crum on Indigo. 97 



weight of any aqueous solution, and nitrate, muriate, and sul- 

 phate of potash, from about 100 times their weight. But the 

 sulphates of magnesia, zinc, and copper, precipitate 2000 times 

 their weight of a solution of phenicin ; sulphate of iron about 

 3000 times ; and alum and muriate of lime as much as 8000 

 times. 



The phenicin being previously combined with a salt of potash, 

 is not altered by being again precipitated by any alkaline salt. 

 These salts do nothing more than saturate the water to such a 

 degree, that the substance is no longer capable of dissolving in 

 it. But the earthy and metallic salts combine with this substance, 

 and displace the salt of potash previously united with it ; and 1 

 have observed very little difference in the quantities necessary to 

 precipitate solutions of different strengths. The precipitates 

 formed by lime, barytes, alum, and copper, are totally insoluble 

 in pure water, however well they may be washed. Those formed 

 by iron and magnesia dissolve to a small extent, when freed 

 from their former menstrua by filtration. Their solution is 

 purple coloured. 



Acids have no effect in preventing the precipitation of pheni- 

 cin by saline bodies ; and the precipitates once formed are not 

 redissolved in the same liquid by the assistance of heat. 



The method which I have given for preparing the new sub- 

 stance is tedious. As only a small part of the indigo is converted 

 into phenicin, the quantity obtained each time is very small, and 

 requires a great quantity of distilled water, and a long time to 

 filter. But if we allow the indigo to be wholly converted into 

 phenicin, its solution cannot be made to pass through any filter, 

 however porous, or however well washed it may have been with 

 water or ammonia. It was by accident that I discovered the 

 possibility of filtering it when only a small portion of the indigo 

 had had time to be changed ; and it was only by preparing it in 

 this manner that I found the purple colour to be owing to the pre- 

 sence of saline matter, and its own colour to belike that of ceruiin. 



The following is a method of preparing this substance in 

 greater quantities, though not so pure. Mix together one part 

 of indigo in powder, and 10 parts of concentrated sulphuric 

 acid, in a phial, and agitate from time to time, till the blue colour, 

 which the indigo loses at first, is completely restored. This, at 

 the ordinary heat of summer, requires nearly three hours. At 

 100° Fahr. it is effected in about 20 minutes ; and indigo mixed 

 with sulphuric acid, at the heat of boiling water, becomes blue 

 the instant the mixture is made. At 45° Fahr. 10 or 12 hours 

 are necessary ; and at lower degrees of heat, a still longer time, 

 supposing always the quantity of materials small enough to cool 

 very soon after mixture to the stated point. Pour this mixture 

 into a large quantity of distilled water, and filter. Take the pre- 

 cipitate off' the filter, wash it well with distilled water, contain- 



New Series, vol. v. n 



