DR. KANE ON THE CHEMICAL HISTORY OF ARCHIL AND LITMUS. 287 
labours of Robiquet and Dumas so fixed in scientific language, that very few persons 
would go back to lichen-red, which in addition does not adapt itself so well to the 
structure of English or French nomenclature as orceine. The word wine-red pig- 
ment is one which could not conveniently be retained in any scientific language ; it 
is totally unfit for expressing the classes of compounds which this substance forms ; 
and as I shall have occasion soon to show that this body is connected in a very inte- 
resting manner with theerytbrine series, the name azoerythrine appears to me one of 
the least objectionable possible. 
In analysing the substances of this group which contain nitrogen, the usual pre- 
cautions were taken to avoid the source of error arising from the formation of nitric 
oxide. In every instance, three inches of the anterior of the tube were occupied by 
clean metallic copper, in the form either of thin sheet clippings, or coarse powder 
freshly reduced by hydrogen. In other respects, the analyses were conducted in the 
manner which has been already described. 
I. Of Azoerythrine. 
Although at first sight there appears to be a considerable quantity of the solid 
material of archil insoluble in spirit, yet when the process already described has been 
followed out, the portion of pure azoerythrine is found to be exceedingly minute, so 
that it is necessary to operate upon a considerable quantity of archil in order to 
obtain sufficient for the purpose of analysis. As prepared from different portions of 
archil, however, its properties appear to be sensibly the same. 
These properties may be deduced in great part from what has been already said. 
Insoluble in water, in alcohol, and in ether, it dissolves in alkaline liquors, giving the 
characteristic port wine colour. This solution is not precipitated by acids. With solu- 
tion of acetate of lead and other metallic salts it gives brownish red precipitates. 
Heated, it gives water and other pyrogenic products, but neither melts nor does it 
volatilize; nor was I able to detect among the products of the action of a moderately 
high temperature upon it, any orceine, as should be found according to Heeren’s 
statement, that his wine-red pigment, when heated, gives off a vapour free from azote, 
and produces lichen-red. The quantity of material at my disposal was however so 
very small, that I do not at all consider Heeren’s statement as being destitute of 
truth. 
The analysis of this substance is liable to difficulty, on account of the possible 
existence in it of traces of another substance, equally insoluble in alcohol, and very 
sparingly soluble in water, and which, although properly a constituent of litmus, yet 
occasionally is to be found in archil, although in very minute quantity. This foreign 
substance (azolitmine) which shall be hereafter described, is turned blue by alkalies, 
and hence whenever the alkaline solution of azoerythrine possesses any slight bluish 
or violet tinge, it may be inferred to be contaminated by the presence of azolitmine, 
and consequently unfit for being used for obtaining numerical results. 
