376

DYEING AND CALICO PRINTING.

through a peculiar kind of looselyAvoven, felty, woollen tissue, which retainsthe ligneous matter, but admits of the passage of the partly dissolved, partlysuspended colourable acids. By the addition of a small quantity of bichlorideof tin, the colourable matters are coagulated, and collected on filters made ofstout linen tissue. After having been once more washed with water the massis dissolved in ammonia, and placed in properly constru&ed tanks, wherein,by the aid of a proper temperature and frequent stirring, the material is con-verted into orchil, an operation which requires a long time. The progress ofthis operation is tested by dyeing, with a certain weight of the orchil, a certainsize of woollen tissue. By this means, also, the end of the operation—thatis to say, the period of highest intensity of colouration—is ascertained.

M. Gauthier de Claubry has observed, and very properly so, that the pro-longed contact of the lichens with water has the effedt of rendering thecolourable matter soluble, so that, unless the operations described are carriedon very rapidly, a loss may be sustained.

Dr. Stenhouse suggests that the lichens should be treated, at the spotswhere they are colle&ed, with milk of lime, 30 per cent of lime of the weightof the lichens ; the liquid filtered, precipitated with hydrochloric acid, and thewhite pasty precipitate filtered off, which, after having been washed and dried,should be conveyed to the orchil manufacturers, since it contains in smallbulk all the really valuable matters of the lichen, while the expense of transportwould become less. The great objection to this plan is, that (while it mightotherwise be also employed in the manufacture of orchil from the lichens broughtto Europe) in contaCt with lime the erythric and lecanoric acids are veryrapidly altered, and the matter spoiled, so that even so short a macerationwith lime as three hours is injurious. Ammonia might be used to extraCtfrom the lichens the colourable acids, but the paste obtained by precipitation withhydrochloric acid is yellowish-brown, owing to the ammonia simultaneouslydissolving a peculiar brown matter present in the lichens. Moreover, thesame objection as for lime holds good for the use of ammonia. When thecolourable principles of the lichens are extracted by prolonged boiling, witheither water alone or water to which an alkaline substance (any alkaline phos-phate, borate, carbonate, or also any caustic alkali) is added, the conversionof the insoluble substances precipitable by acids into soluble matters no longerprecipitable is rapidly brought about, and therefore the liquids have to be con-centrated by evaporation.

The ordinary method of preparing orchil paste is as follows :—The apparatusused is a wrought-iron horizontal cylinder, made very smooth within, about6 feet in length and 3 feet in diameter. The lowest third part of the circum-ference, for the entire length, is fitted with a steam-jacket for the applicationof heat. A shaft runs through the cylinder axially from end to end, fittedwith paddles and worked by steam-power, in order to agitate the mass.Along the top runs a slit from end to end, with a movable lid, for introducingthe charge of weed and ammonia. There are also a few small slides for regu-lating the supply of air. In the front of the cylinder, below the axle of theagitator, is a man r hole, for discharging, and above the axle, right and left, aretwo small slides for the admission of air. A cylinder, of the dimensionsgiven, is charged with 180 lbs. of weed and 540 lbs. ammonia, at 5° of thecommon ammonia-glass, which corresponds almost exactly with Baumes