Mr. J. Dalton on the Nature and Properties of fncligo. 125 



' I am inclined to think the analysis of Mr. Crum as likely 

 to be an approximation to the constitution of pure indigo as 

 either of the other two ; and I should adopt his atomic con- 

 stitution, if he would modify it so as to adopt my weight of the 

 atom of azote instead of its double, which has somehow got 

 into common reception as a substitute without any sufficient 

 reason that I can find. If we adopt my weight for azote, 

 Mr. Crum's atoms will become 16, 2, 2, and 4; which, bemg 

 all divisible by 2, become 



8 atoms carbon 



1 atom oxygen 



1 atom azote 



2 atoms hydrogen 



12 



This simplification of the atom of indigo I suggested to 



Mr. Crum in a conversation we had together, and he seemed 



inclined to adopt it. Referring therefore to my scale of atomic 



numbers, we shall have the atom of pure indigo to consist of 



8 atoms carbon 5-4- = 43'2 75*5 



1 atom oxygen 7 = 7 12-3 



1 atom azote 5=5 8*7 



2 atoms hydrogen 1=2 3-5 



57-2 100 



Mr. Crum, in his very ingenious essay above referred to, 

 finds that a compound of one atom of indigo and one of water 

 may be formed by means of sulphuric acid : he denominates 

 \iphenicin; it may perhaps be better designated by the name 

 of proto-i^.ydrate of indigo. The common product of sulphuric 

 acid and indigo, or sulphate of indigo of Dr. Bancroft, he calls 

 ceridin, and finds it to be a compound of one indigo and two 

 of water, or the deuto-hydrate of indigo. 



I have made no attempts myself to analyse pure indigo into 

 its constituent elements, but have often tried, both recently 

 and some years ago, to find the quantity of oxygen required 

 to convert the green indigo solutions in lime-water into blue 

 indigo. The results have been pretty uniformly the same— 

 naniely, that the oxygen which combined with the green in- 

 digo, to convert it to blue, was about one-seventh or one-eighth 

 of the whole weight of the resulting indigo ; and lience I 

 concluded, on the supposition that one atom of oxygen was 

 added to one of indigo, that the atom of indigo must weigh 

 about 55, or 5Cy, and this conclusion I pointed out toMr.Crum, 

 as corrol)oraling his analysis. The quantity of oxygen re- 

 quired was nnich less, and of course the weight of the atom 

 ()rin<lig<> was much greater than I had anticipated. 



We 



