DR. KANE ON THE CHEMICAL HISTORY OF ARCHIL AND LITMUS. 299 
ing material; or 2nd, the reddish brown mass may be boiled in water of ammonia, in 
which it dissolves, giving a blue solution. When this is evaporated to dryness, the 
greater part of the ammonia separates, and to remove the last traces, the residual 
mass may be moistened with dilute muriatic acid, and then washed with alcohol 
until the excess of acid and the sal-ammoniac have been removed. To this substance 
I give the name of Azolitmine. 
The blue liquors which are obtained in the first place, by digesting the litmus 
cakes in boiling water, contain but a very small quantity of colouring matter, in 
comparison to what might be expected from the great depth of colour they present. 
To obtain this colouring matter in a pure condition, a solution of acetate of lead is to 
be added, and the purple precipitate which falls, having been well washed, is to be 
treated while still moist with a current of sulphuretted hydrogen, until completely 
decomposed. The resulting compound of the colouring matter with the sulphuret 
of lead is to be very well washed to remove all excess of sulphuretted hydrogen, and 
then digested in warm water of ammonia: a deep blue liquor is obtained, which is 
to be evaporated to dryness, and then moistened with muriatic acid and washed with 
warm alcohol to remove the sal-ammoniac which is formed. The colouring mate- 
rial remains as a deep brown-red powder. 
In most cases this substance will be found to be azolitmine nearly pure, but I 
have met it totally free from azote, and to constitute a peculiar substance, resembling 
azolitmine in properties, but remarkably distinct from it in constitution. This 
substance is very rare in litmus. It constitutes but a very unimportant portion of 
the colouring substance, and hence I propose, for the adoption of chemists, the name 
Spaniolitmine, to distinguish it from the constant constituents already noticed, the 
Greek word anavioc signifying rare. 
The colouring constituents of litmus are therefore in their natural condition red, 
and the blue of litmus is produced by combination with a base. There are, properly 
speaking, only two characteristic colouring matters in litmus, the erythrolitmine and 
the azolitmine. For the erythrolein is coloured crimson purple only by alkalies, and 
the spaniolitmine occurs but very seldom. In the litmus of commerce these colour- 
ing substances are combined with lime, potash, and ammonia, and there is mixed up 
in the mass a considerable quantity of chalk and sand. 
I shall now proceed to the detailed account of the constitution and properties of 
these various substances. 
I. Of Erythrolein. 
This substance, as obtained by evaporating the ethereal solutions, is semifluid at 
ordinary temperature, and completely liquid at 100° Fahr. Its solution in ether is 
of a very fine red colour. It dissolves in alcohol with the same colour, and tinges 
water pink, without however dissolving in any very sensible proportion. It is inso- 
luble in oil of turpentine, and dissolves in water of ammonia, with a magnificent 
2 q 2 
