DR. KANE ON THE CHEMICAL HISTORY OF ARCHIL AND LITMUS. 
275 
same ultimate coloured substance? These are questions which it will be at once 
seen all preceding researches leave quite untouched, and they must evidently be, at 
least in great part, solved before any considerable portion of light can be thrown 
upon this difficult part of science. 
I do not pretend to have established in the present paper a complete solution of 
those difficult questions. In fact, months of continued investigation have proved to 
me, that the subject is still more complex than the statement above given would 
point it out to be. If my results appear to have placed the problem of the origin and 
constitution of these bodies in a more definite light than that in which it had pre- 
viously been contemplated, and to have shown at least the difficulties of the subject, 
if not positively to have removed any of them, I shall consider the object for which I 
now submit to the scientific world these contributions to our knowledge in this de- 
partment, as sufficiently attained. 
The object of the present paper being threefold, viz. first, to ascertain the primi- 
tive form of the colour-making substance in a given species of lichen, and trace the 
stages through which it passes before the coloured substance is developed ; secondly, 
to determine the nature of the various colouring substances which exist in the archil 
of commerce ; and thirdly, the examination of the colouring materials of ordinary 
litmus ; it will be found convenient to divide the paper into three sections under these 
three heads, and to treat of the subjects in the order above described. Through the 
kindness of a friend I was enabled to procure, in sufficient quantity, a lichen now used 
extensively in Liverpool in the manufacture of archil of a very superior kind; this lichen 
was ascertained by an eminent botanist to be the Roccella Tinctoria : it is imported 
from the Cape de Verd Islands, under the name of archil-weed, and generally sells for 
200/. per ton : some specimens which I procured were of so fine a quality as to be 
valued at 320/. per ton. The archil and the litmus used in these researches were 
derived indifferently from various sources in Liverpool, London, and Dublin. 
Section I. Chemical Examination of the Roccella Tinctoria ( Archil-weed ). 
The treatment to which the lichen should be subjected in order to obtain from it 
the peculiar principles which it contains, I found after many trials, to be best arranged 
in the following manner. Having been first chopped very small, it is to be digested 
in successive quantities of alcohol kept just below boiling (about 140° Fahr.) for 
some hours, in a retort connected with a condensing apparatus, by which the vapor- 
ized portion of spirit may be collected and subsequently used. When by this means 
all matters soluble in spirit have been dissolved out, the solutions are to be united, 
and the spirit distilled off in a water bath, until the residue in the retort becomes 
dry. A mass of a yellowish colour is thus obtained. This mass is to be then boiled 
in water for a few minutes, and the liquor then filtered as rapidly as possible whilst 
very hot. What remains undissolved may be again treated by boiling in water, as 
long as any portion of it appears to dissolve. 
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