XX. Examination of the yroximate Principles of some of the Lichens . — Part II. 
By John Stenhouse, F.R.S. 
Received February 14, — Read March 29, 1849. 
Gyrophora pustulata*. 
This lichen has been long employed in the manufacture of archil, though the quan- 
tity of colouring matter contained in it is by no means considerable, being little more 
than a twelfth of that in the Roccella Montagnei. 
The Gyrophora pustulata is the Tripe de Roche of the Canadian hunters, who, not- 
withstanding its disagreeably bitter taste, occasionally use it as an article of food in 
seasons of scarcity. A memorable instance of this occurred in the case of Messrs. 
Frankltn and Richardson, who during their disastrous journey to the shores of the 
Polar sea, after the failure of their supplies, subsisted almost entirely upon this lichen 
during several weeks. The Gyrophora pustulata, on which I operated, was brought 
from Norway, where it is annually collected in considerable quantity for the manu- 
facture of archil. The colouring principle was extracted by maceration with milk of 
lime, and was precipitated in a gelatinous state by neutralizing the lime solution by 
muriatic acid, precisely in the way so frequently described in the first part of this 
paper. I may mention however that the most convenient mode of effecting this ope- 
ration on a considerable scale, is to steep the lichens, previously cut into small pieces, 
for some hours in water till they are thoroughly soaked. They should then be strati- 
fied with a great excess of slacked lime in a large barrel furnished with a false bottom 
pierced with small holes, under which a spigot is placed; in fact, in exactly such an 
arrangement as is employed by the soap-makers for preparing caustic lyes. Water is 
then poured into the top of the barrel, and when it has remained on the mixture of 
the lime and the lichens for an hour or so, it is drawn off by opening the spigot, when 
the solution runs off quite clear of a deep brownish colour. Water is still added in 
successive quantities so long as the lime solution, when neutralized by muriatic acid, 
continues to afford a precipitate. The great advantage of this arrangement is, that 
it can be easily and rapidly executed on a large scale, and that the extraction and 
filtration are effected by a single operation. 
The gelatinous precipitate from the lichen, which had a reddish brown colour after 
being washed with cold water by decantation to remove adhering muriatic acid, was 
collected on a cloth filter and dried by a very gentle heat. When the greater portion 
* I am indebted to the kindness of John King, Esq., of George M'Intosh and Cot, chemical manufacturers, 
Glasgow, for the lichens employed in this part of the investigation. 
