On Indigo. 433 
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 num ers, we shall have the atom 
of pure indigo to consist of 
8 atoms carbone 5.4 = 49.2......... 73.5 
1 atom oxygen a= Move nalsiae 12.3 
1 atom azote ea ectes es ree 8.7 
2 atoms hydrogen Lo == 2 eseeveree 3.5 
57.2 100 
Mr. Crum in his very ingenious essay above 
referred to, finds that a compound of J atom 
of indigo and | of water, may be formed by 
means of sulphuric acid; he denominates it 
phenicin; it may perhaps be better desig- 
nated by the name of proto-hydrate of indigo. 
The common product of sulphuric acid and 
indigo, or sulphate of indigo of Dr Bancroft, 
he calls cerulin, and finds it to be a compound 
of 1 indigo and 2 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 
3.1 
