64 
MR. STENHOUSE ON THE EXAMINATION OF THE 
I. The South American variety of Roccella tinctoria. 
This lichen, which is imported in considerable quantities from the west coast of 
South America, is found, I have reason to believe, in the neighbourhood both of 
Lima and of Valparaiso. It is a large and handsome lichen from six to eight inches 
long, and its stems are in some instances as thick as those of a goose-quill. It was 
pronounced by Dr. Scouler to be a large variety of the J?. tinctoria. The lichen, 
after being cut into small pieces, was macerated with a considerable quantity of 
water for some hours, so as to moisten it completely ; a quantity of quicklime was 
then put into the liquid ; the whole was well-stirred and then suffered to repose. 
The clear liquid, which had a slightly yellow colour, was then drawn off and filtered. 
The mixture of the lime and lichen had about half as much water poured on it as 
before, and after standing for a quarter of an hour this was also drawn off, filtered 
and mixed with the first quantity. ’In order to exhaust the lichen completely, it 
should be treated with a considerable excess of lime, but care should be taken not 
to permit the lichen to remain very long in contact with the lime, otherwise the 
colouring principle will be oxidized and rendered brown. An excess of muriatic acid 
was then added to the lime solution, when the whole of the colouring principle of 
the lichen Avas precipitated as a white gelatinous bulky mass. When this gelatinous 
precipitate had been repeatedly washed by decantation to remove adhering muriatic 
acid, it was collected on a cloth filter, and dried upon a plate of gypsum. When 
pretty well freed from moisture, it was dissolved in hot spirits of wine, but at a tem- 
perature much under boiling, as otherwise an ether compound would have been 
formed. On the cooling of the solution, the colouring principle was deposited in 
small white prismatic needles arranged in stars. Should these crystals not be quite 
colourless, they may be easily rendered perfectly so by redissolving them in alcohol, 
and digesting them with a little purified animal charcoal. The above is the best 
process for procuring the colouring principle of this lichen, to which I shall give the 
name of Orsellic acid, in a state of purity. Orsellic acid may also be obtained, but 
much less economically, as the greater portion of it is then destroyed, by boiling the 
lichen in large quantities of water, and then purifying the precipitate obtained by 
repeatedly crystallizing it out of weak spirit. This is the process by which Mr. 
ScHUNCK has extracted erythric acid from the Angola lichen. Besides the great loss 
of the acid which this method occasions, I have always found that the orsellic acid 
extracted by hot water, even after repeated crystallizations out of alcohol, is never 
free from traces of a resinous matter and of a fatty acid, which I could only remove 
by dissolving it in cold lime or baryta water, and purifying it in the way already 
described. 
{Alpha) Orsellic Acid. 
Orsellic acid is nearly insoluble in cold water, but it dissolves, though sparingly, in 
boiling water, from which it is deposited in small prisms arranged in stars. It is 
K 
