160 ORCHIL. 



ture is tiuly tropical ; but it seems probable that indigo can never 

 be advantageously introduced into the agriculture of temperate coun- 

 tries. 



Before indigo was so extensive an article of commerce as it is 

 now, the south of France used to furnish almost all the marketvS of 

 Europe with a blue dye, which was the best then known ; this was 

 woad or pastel, the produce of the Isatis tinctoria. 



The isatis is sufficiently hardy to stand the cold of winter. In 

 the south it is sown in March, and the seed springs in from eight to 

 ten days. When the plant has five or six leaves, it is hoed with 

 care. The crop is gathered when the leaves have acquired their 

 greatest size, when they even begin to fade a little. The prepara- 

 tion of woad bears a certain resemblance to that of indigo, and need 

 not detain us here. 



The Polygonum tinctorium has of late attracted the attention of 

 European cultivators. The plant is a native of China, where it has 

 been cultivated from time immemorial ; it was brought into France 

 and propagated under the care of M. de Lille. In the course of 

 three months the plant has thrown out all its leaves, and in the south 

 of France it never fails to ripen its seeds. From some experiments 

 that have been made, the leaves of the polygonum appear to contain 

 about the five-thousandth of their weight of indigo, and as the acre 

 of land will yield between 11,000 and 11,900 lbs. weight of leaves 

 the produce of coloring matter will come to upwards of 56^ lbs. 



The indigo obtained from the polygonum by the methods generally 

 practised is not always of fine quality. It contains matters which, 

 having been dissolved in the water used for maceration, had subse- 

 quently been precipitated M. Vilmorin proposed to adopt on the 

 great scale and in the manufactory, the methods which are used for 

 purifying indigo in the laboratory, and which consists, as we have 

 seen, in reducing colored and insoluble indigo to the colorless and 

 insoluble state by means of a salt of the protoxide of iron in contact 

 with an alkali, and subsequently to restore its color, and effect its 

 precipitation by contact with the oxygen of the air. It is obvious 

 that this method is perfectly applicable to the treatment of the whole 

 of the indigoferous plants, and I believe that its adoption would be 

 a great improvement. 



Orchil. This coloring matter, of a deep purple, is prepared from 

 certain lichens or lung-worts ; that which is most prized is the rocella 

 tinctoria, a native of the Canaries and Cape de Verd islands. The 

 variolaria dealbata, the var. aspergillia, and the lichen corallinus, 

 which grow upon the rocks of Auvergne, and on the Alps and Pyre- 

 nees, yield a produce of inferior quality. 



To obtain the orchil, the lichens are steeped for several days in 

 their own weight of stale urine. Into the mixture about 5 per cent, 

 of slaked lime in powder, a small quantity of arsenious acid, and a 

 little alum, are introduced. Fermentation is by and by set up in the 

 mass, which soon acquires the characteristic color of the orchil, but 

 the tint is never complete until the expiration of about a month. 



Orchil readily communicates its peculiar color to water and to al« 



