78 
MR. STENHOUSE ON THE EXAMINATION OF THE 
These numbers agree pretty well with the formula O^o, which however is 
merely empirical, as I have been quite unable to form any compound with pseudo- 
orcin so as to determine its atomic weight. Pseudo-orcin appears to be an exceed- 
ingly indifferent substance with properties intermediate between those of orcin and 
mannite. 
Mode of extracting the Colouring Principles of the Lichens employed hy the Archil 
makers, so as to render them more portable for commercial purposes. 
The amount of colouring principle contained in even the richest of the lichens 
employed by the archil manufacturers, bears but a small proportion to the weight of 
the lichen itself. In the case of the Roccella Montagnei from Angola, it amounts to 
about twelve per cent. ; in the South American lichen to about seven ; and in the 
Cape variety and in the Lecanora tartar ea it varies from about two to one and a 
half per cent. From the great distances from which most of these lichens must be 
brought, the cost of their transport is so considerable as materially to diminish their 
commercial value. This is especially the case with their poorer varieties. I think it 
would in many cases therefore be found advantageous to extract the colouring matter 
in the countries where the lichens grow, and as this can be effected very readily, a 
large proportion of the expense of their transport might be easily saved. All that 
would be necessary for this purpose would be to cut the lichens into small pieces ; to 
macerate them in wooden vats with milk of lime, and to saturate the solution either 
with muriatic or acetic acid. The gelatinous precipitate could then be collected on 
cloths and dried by a gentle heat. Almost the whole of the colouring matter in a 
lichen could thus be easily extracted at a comparatively small expense, and the value 
of the dried extract, amounting to more than a thousand pounds per ton, would 
abundantly defray the expense from even the most distant inland localities, such as 
the Andes or the Himalayas. 
Mode of estimating the quantity of Colouring Matter in the Lichens. 
A solution of hypochlorite of lime affords a very ready method of approximating 
pretty closely to the amount of red colouring matter contained in a lichen. Any 
convenient quantity of the lichen, say one hundred grains, may be cut into very 
small pieces and then macerated with milk of lime till all the colouring principle is 
extracted. Three or four macerations are quite sufficient for this purpose if the 
lichen has been sufficiently comminuted. The clear liquors should be filtered and 
mixed together. A solution of bleaching powder of known strength should then 
be poured into the lime solution from a graduated alkalimeter. The moment the 
bleaching liquor comes in contaet with the lime solution of the lichen, a blood-red 
colour is produced which disappears in a minute or two, and the liquid has only a 
deep yellow colour. A new quantity of the bleaching liquid should then be poured 
into the lime solution and the mixture carefully stirred. This operation should be 
