1823.] Mr. Crum on Indigo. 83 



and applying the heat of a spirit-lamp till all the sublimed indigo 

 is formed upon the surface of the ashes. On repeating this pro- 

 cess, I find that ten parts of common indigo yield one of sub- 

 limed indigo, which is, however, far from being pure. By 

 resublimation in my apparatus, it is again reduced one-half from 

 the loss of its impurities, and some vapour. 



I shall here describe what else takes place during the sublima- 

 tion. Ten grains of precipitated indigo in the apparatus I have 

 described yielded 



1*88 grain of sublimed indigo. 



6-44 grains of cinder remained, and consequently 



1 -68 grain of volatile matter escaped. 



10-00 



Thirteen grains of the same indigo, kept a quarter of an hour 

 at a strong red heat in a small platina crucible, firmly, though 

 not exactly closed, left 7*9 grains of cinder, which is equal to 

 61 per cent. 



In order to ascertain what gases were evolved during this 

 destruction of the indigo, I introduced 5"28 grains into a small 

 glass tube connected with a mercurial trough. On applying the 

 heat of a spirit-lamp, the vapour of indigo was formed, and 

 condensed in the colder part of the tube, but was at last 

 destroyed by repeated applications of heat, A quantity of water 

 appeared in the tube, and 0*96 cubic inch of gas was found 

 in the receiver. On removing the tube, it was found to have lost 

 in weight 0-71 grain, or 13-5 per cent, of the indigo employed. 

 The water that was formed had a disagreeable burnt ammonia- 

 cal smell. 1 found, on analyzing the gas in the receiver (making- 

 allowance for the common air of the apparatus, and a small por- 

 tion of gas remaining in the tube), that it consisted for 100 of 

 indigo of 



Carbonic acid 2*8 



Carburetted hydrogen and carbonic oxide 0*8 



Azote 1-9 



The difference between the sum of these and the 

 loss 13-5 was water, with a little ammonia 8*0 



13^5 



Sublimed Indigo. 



Indigo sublimes in long- fiat needles, which readily split when 

 they are bruised into four-sided prisms. 



Viewed at a particular angle, they have the most brilliant and 

 intense copper colour ; but when lying in heaps, they have a 

 rich chesnut-brown colour; one that would be produced by mix- 

 ing a very little yellow with a bright but deep reddish purple. 



Besides these needles, this substance is found in the form of 



g2 



