XX. Examination of the proximate principles of some of the lichens. — Part II

Abstract

Gyrophora pustulata*. This lichen has been long employed in the manufacture of archil, though the quantity 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 manufacture 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 operation 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 stratified 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.