314 DR. KANE ON THE CHEMICAL HISTORY OF ARCHIL AND LITMUS. 
It results from these experiments, that precisely as the colouring matters com- 
bine with water to form different shades of red coloured bodies — with ammonia 
(amidide of hydrogen) to produce a series of bodies which are blue or purple — so they 
combine with sulphuret of hydrogen to form colourless compounds in solution, which, 
if solid, would very probably be white. I attempted frequently to obtain these com- 
pounds solid, but without success, the sulphuretted hydrogen escaping at ordinary 
temperatures, and the substance being soluble both in water and in spirit, rendered 
my trials useless. The equivalency of these three series of bodies is evident, however, 
when we compare 
c 18 h 10 no 10 + ho 
C 18 H 10 NO 10 + HAd 
C 18 H 10 NO 10 + HS. 
The similarity of character which pervades oxygen, amidogene, and sulphur is mani- 
fest in other departments of organic chemistry ; precisely therefore as these colouring 
matters combine with metallic oxides and metallic sulphurets, so may we expect to 
discover at some future period, bodies consisting of them in union with metallic ami- 
dides. 
In addition to the action of sulphuretted hydrogen, the colouring matters of litmus 
may be blanched by other deoxidizing agents of a very distinct character, and whose 
action it will be of the highest interest to be able to study in detail. It had been long 
known that by means of nascent hydrogen, the colours of a great variety of flowers 
might be removed, and I have found that in this way all the various colouring sub- 
stances of litmus and of archil may be rendered white, and converted into new bodies, 
an exact examination of which is very difficult. The coloured bodies may also be 
reduced to the white condition by means of those metallic oxides which powerfully 
attract oxygen, as the protoxides of tin and iron, and in these white conditions they 
combine with the various bases to form salts or lakes, which on exposure to the air, 
rapidly become red or purple. In all these cases the reaction appears at first sight 
almost necessarily to consist in the removal of oxygen, but it will be found that there 
is very full evidence against that opinion, and that in reality the change results from 
the addition of a certain quantity of hydrogen to the substance. These white sub- 
stances I propose to indicate by the initial word Leuco (from XevKoc, white), and there 
is no doubt but there exists one for each coloured matter, but I have only obtained 
numerical or exact results with two, the leucolitmine formed from azolitmine, and 
the leucorceine formed from the betaorceine. 
When a solution of orceine in water of ammonia is rendered slightly acid by mu- 
riatic acid, and a slip of zinc immersed in it, the liquor becomes after some time 
perfectly colourless, but recovers its original red tinge rapidly when exposed to air. 
If to the colourless solution water of ammonia be added, a copious white precipitate 
is produced, which very soon becomes pink, and ultimately purple, on exposure. To 
