43 §

DYEING AND CALICO PRINTING.

been thickened with gum-water, is printed and steamed. The following sub-stances may, if desired, be added to the lake:—Phosphate of soda, eitheralone or mixed with pasty hydrated binoxide of tin, binarseniate of potassa,alone or with the same preparation of tin.

When silk or wool is put in a bath made up of extradt of chlorophyl(sp. gr. I'oyo), and containing phosphateof soda and oxide of tin, very deepshades are produced.

It is a well-known fa< 5 t that dead wood often exhibits a green colour : suchwood yields, when treated with chloroform, a beautifully bluish-green matter,which differs from chlorophyl by its chemical properties, and has been namedxylochloric acid.*

The flowers of the tree Sophora Japonica, a native of Japan and China,belonging to the Leguminoseae, yield a yellow and green pigment, the formerbeing, according to Dr. Stein, identical with the rutinic acid obtained from theflower-buds of the Capparis spinosa, and occurring in the Rnta gravcolens.The yellow flowers of the tree known in China as hwae or hoal are collectedjust before they begin to fade, sun-dried, moistened with the juice of someother flowers which are pounded along with salt in a mortar, formed into theshape of small balls, and next gently dried in the shade. When it is desired todye silk yellow by means of this preparation, the silk is first steeped for twelvehours in a solution of alum, and next placed in a boiling decodtion of the hoal.MM. Michel and Guinon state that the colouring matter only exists in theflowers. Alkalies redden the pigment, acids discolour it; bichromate ofpotassa turns the colour a bright mahogany-brown. In order to dye greenwith this substance the Chinese make use of the adtion of sunlight: they im-merse, according to the statement of M. Madows, the cotton in a boilingalumed solution of hoal, and repeat this operation frequently. After dryingthe cloth so treated, each time by exposure to sunlight, the late Mr. WalterCrum obtained, by following this method, only a faint green.

Blue Colouring Substances.

We have already cursorily noticed some blue and bluish-violet colouringmatters of vegetable origin. Such blue substances, however, are pradtically oflittle use : the only immediate blue vegetable principle which deserves ourattention is indigotin, a nitrogenous perfedtly well chemically-defined prin-ciple, the produce of several plants, and probably also generated under certainconditions in the animal organism.

We shall first speak of indigotin as a chemical substance, without takinginto account its variable origin. We shall next describe the natural history ofthe plants wherein indigotin is formed, and the industrial preparation of indigo,its qualities and applications.

Indigotin has not been hitherto artificially produced with certainty, and therelations it bears to one or other of the great series of organic chemistry areonly imperfedtly ascertained : the elementary ultimate composition of indigotinis perfedtly well known, and its formula, C8H5NO, or any multiple thereof, isthoroughly controlled by a great number of derivatives.

Indigotin may be obtained in a crystalline state by sublimation, and in thatcase the crystals exhibit a coppery refledtion. If reduced to powder it is deep

* Forclos, “ Rcpcvtoiie de Chimie Appliquee,” v., 331,1863.