452 DYES AND COLORING STUFFS . 



of purity, and make it up in homogenous masses in imitation of 

 pipe gamboge, the finest Siam variety. It seems to possess more 

 coloring matter, more resiii and less gum than the ordinary gam- 

 boge of commerce. Gamboge owes its color to the fatty acid. 

 The resin must be regarded as the chief constituent, and is most 

 abundant in that imported from Ceylon, which contains about 76 

 per cent., and is therefore best adapted for painting. Gamboge 

 also has its medicinal uses. 



Various species of Lecanora, particularly L. tartarea, known as 

 cudbear, are used in dyeing woollen yarn, The Rocella tinctoria 

 and fusiformis furnish the orchil, or orchilla weed of commerce, 

 which is sometimes sold as a moist pulp, but usually in the form of 

 dry cakes, known under the name of litmus; it produces a fine purple 

 color. Our imports, which have amounted to 6,000 or 7,000 cwts. 

 annually, are derived chiefly from the Canary, Azores, and Cape 

 Verd Islands. Rock orchilla was shown at the Exhibition, from 

 the Berlingen Isles, from Angola, Madeira and the Cape de Verds. 

 Orchilla w r eed is very plentiful about the shores of the islands of 

 New Zealand, some being sent from thence to the Exhibition ; 

 but from a want of knowledge as to the time at which it should 

 be gathered, and the mode of preparing it for the market, it has 

 not yet become a saleable commodity there. The rich varieties 

 of lichens on the rocks and plains of Australia have not been 

 tested, as they ought to be, with Helot's lichen test. Various 

 lichens, and Mocella tinctoria, from Tenasserim and other parts of 

 India, have been introduced by the East India Company. In the 

 Admiralty instructions given to Capt. Sir James C. Ross, on his 

 Antarctic voyage, a few years ago, his attention was specially called 

 to the search and enquiry for substitutes for the Rocella, which 

 is now becoming scarce. A prize medal was awarded, in 1851, to an 

 exhibitor from the Elbe for specimens of the weed, and an extract 

 of red and violet orchil. Specimens of varieties of the lichens 

 used in the manufacture of cudbear, orchil and litmus, and of the 

 substance obtained, were also shown in the British department, 

 which were awarded prize medals. 



The beauty of the dyes given by common materials, in the 

 Highlands of Scotland, to some of the cloths which were exhibited, 

 should lead our botanists and chemists to examine, more closely 

 than they have hitherto done, the dye-stuffs that might be ex- 

 tracted from British plants. "Woad (Isatis tinctoria) and the 

 dyers' yellow woad (Heseda lutea), are both well known. A piece 

 of tweed, spun and woven in Ross-shire, was dyed brown and black, 

 by such cheap and common dyes as moss and alder bark, and the 

 colors were unexceptionable. 



Sutherlandshire tweed and stockings, possessing a rich brown 

 color, were produced with no more valuable dye than soot ; in 

 another piece, beautifully dyed, the yellow was obtained from 

 stoney rag, brown from the crops of young heather, and purple 

 from the same, but subjecting the yarn to a greater action of the 

 dye than was necessary to produce brown. There is very little 



