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DYEING AND CALICO PRINTING.

turns blue by the oxidising adtion of the atmosphere, and is converted intogreen by a yellow dye.

According to M. Persoz’s opinion, the Chinese green-dyed cotton is, like allgreens of organic origin (excepting aniline green), the result of a combinationof blue and yellow, and he also thinks that there is no ground at all for sup-posing that the green dye imparted to cotton in China and the pigment knownas lo-kao are identical, because in the former the yellow, and in the latter theblue, predominates. This opinion is strengthened by the fadt that the processof dyeing of M. Michel produces upon silk a colour which is a bluish-green,and only by the aid of picric acid can this be converted into a pure green.

If desired to dye cotton a green with lo-kao the following process is recom-mended by M. Persoz :—From 50 to 60 grms. of white soap are dissolved in10 litres of water, to which is added a sufficient quantity of lo-kao, previouslysteeped and consequently swollen in water, or, better yet, the purifiedpigment. The liquid so obtained is heated, and the cotton, on immersion, isat once dyed.

For the purposes of printing the cotton fabric may be alumed first, but thisis not indispensable. The colour consists of gum-water wherein lo-kao, pre-viously steeped and swollen up, is finely divided, or an aluminous lake maybeused, with or without the addition of acetate of alumina. Another plan is toprint on a thickened solution of lo-kao in tin-salt: after drying, the fabric ispassed through a solution of acetate of lime, to which an excess of lime isadded. Cotton may be dyed, also, with a solution of lo-kao in sulphydrateof ammonia, followed by a well-condudted exposure to air.

M. Persoz has succeeded in fixing lo-kao on woollen fabrics by preparingfirst a tin lake of that pigment: this lake is suspended in water, which is nextheated, and the wool being entered, and some drops of a solution of oxalicacid added, it becomes perfedtly dyed. The same lake may be thickened withgum-water acidulated with oxalic acid, and printed on to woollens andworsteds, yielding, after steaming, a beautifully green colour.

The beautiful shades of green as obtained from lo-kao have almost disap-peared from the market, first, from their want of stability, and, secondly,because of the discovery of the coal-tar colours.

Lo-kao is also noticeable as being the only substance we are acquaintedwith capable, with proper reagents, of producing all the seven colours of thespedtrum. Though driven from the market, it remains an interesting sub-stance.

It is an interesting fadt, that while the greens produced by indigo and picricacid appear blue in artificial light, those produced with Prussian blue andpicric acid appear green under the same conditions.

Other Green Dyes of Vegetable Origin.

We will now briefly notice some green pigments and dyes which have beennoticed, but are, after all, very little known in Europe, and which may beidentical with or analogous to Chinese green.

M. Poivre, French Minister-Plenipotentiary in Cochin China (1749), andFather Horta, who visited that country as a missionary (1766), speak of a plantcalled Tsai, which was cultivated in Cochin China and neighbouring countries,and which plant, on being fermented, as indigo usually is, produced by that