CHAMBERS'S INFORMATION FOR THE PEOPLE. 



boiled with acids, yields a sweet substance, and a 

 colouring principle called ' quercetine.' It is used 

 as a yellow dye. 



Persian or Turkey Berries. The fruit of various 

 species of Rhamnus. They are used for dyeing 

 morocco leather and wool yellow. The Rhamnus 

 catharticus yields the pigment called ' sap green.' 



Turmeric the root of Curcuma longa and 

 Curcuma rotunda is used for dyeing silk and 

 wool yellow. Its colouring-matter is curcumin 

 (C 8 H 10 O 2 ). Paper stained yellow with turmeric is 

 used as a test for alkalies and for boracic acid, by 

 which it is rendered brown. 



Annatto or Arnotto, a yellowish-red colouring- 

 matter, prepared from the fruit of Bixa orellana, 

 It is used as an ingredient in varnishes, for 

 dyeing silk, and for colouring cheese and 

 butter. 



Weld is the dried plant Reseda luteola, a plant 

 belonging to the same genus as mignonette. The 

 colouring-matter is called luteoline. It is used as 

 a yellow dye. 



Safflower consists of the dried petals of Car- 

 thamus tinctorius, a thistle-like plant cultivated in 

 the Levant, Egypt, India, Southern Russia, Cen- 

 tral Germany, Hungary, Italy, Spain, and South 

 America. It contains two colouring-matters 

 one yellow, soluble in water, which is not used 

 as a dye ; the other red, insoluble in water, but 

 soluble in alkalies. This red colouring-matter 

 is called carthamine, and has the composition 

 C 14 H 16 O T . Safflower is used for dyeing silk red. 

 Carthamine, mixed with French chalk, constitutes 

 the rouge used as a face-powder. 



Orchil and Cudbear. These are red dye-stuffs 

 prepared from various lichens. The colouring- 

 matter is orceine (C 7 H 7 NO 3 ). The blue colouring- 

 matter 'litmus' is obtained from the same lichens. 

 Its colouring principle is called azolitmine, and 

 appears to have the composition C 7 H 7 NO 4 . Paper 

 stained with litmus is used as a test for acids, 

 which change the colour to red ; and reddened 

 litmus-paper is used as a test for alkalies, which 

 restore the blue colour. 



PIGMENTS AND DYE-STUFFS OF ANIMAL ORIGIN. 



Of these, the most important are Cochineal, Lac, 

 and Purree. 



Cochineal. True cochineal consists of the 

 bodies of the female Coccus cacti, an insect found 

 on various species of cactus in Mexico, Spain, the 

 Canary Islands, Algeria, and Java. The insects 

 are collected after they have laid their eggs, and 

 are killed by being subjected to the action of 

 steam, or by the heat of an oven. Carmine is 

 the colouring-matter prepared from cochineal by 

 various processes, kept secret by the makers. It 

 owes its beautiful red colour to carminic acid 

 (C 14 H 14 O 8 ), a red solid, soluble in water and 

 alcohol. Carminic acid appears to be a gluco- 

 side, and yields, when boiled with dilute sulphuric 

 acid, a special kind of sugar, and a substance 

 called carmine-red. 



Lac is the product of an insect, Coccus lacccz, a 

 native of India and the East Indian Islands. 

 The female insect punctures the twigs of various 

 trees and shrubs, and lays her eggs in the milky 

 juice which exudes. This juice hardens into a 

 resinous mass, 'which incloses the eggs and the 

 dead bodies of the parent insects. The cater- 



344 



pillar, emerging from the egg, eats its way through 

 the surrounding resin. Lac occurs in commerce 

 in three forms : i. Stick-lac that is, lac in its 

 natural state, adhering to the twigs from which it 

 was formed ; 2. Seed-lac that is, lac picked off 

 from the twigs, and deprived by treatment with 

 water of some of its colouring-matter ; and 3. 

 Shell-lac that is, lac which has been fused and 

 strained through a cloth, and has thus lost nearly 

 all its colouring-matter, and consists almost 

 entirely of lac-resin. Shell-lac is used for the 

 manufacture of sealing-wax ; dissolved in alcohol, 

 it forms the common spirit-varnish. Lac-dye is 

 obtained from stick-lac, which contains about 10 

 per cent, of colouring-matter. It is probably pro- 

 duced by the insect, as it bears a close resem- 

 blance to cochineal, the product of the Coccus 

 cacti. 



Purree is a substance the origin of which is 

 unknown. It is imported from India and China 

 in rounded masses of 3 or 4 oz. weight, and is 

 used for making the pigment Indian yellow. It 

 is generally believed to be of animal origin, and 

 to be derived from the urine of camels and ele- 

 phants. The colour is due to the euxanthate of 

 magnesia. Euxanthic acid has the composition 

 C S1 H 18 O U . 



PAINTS consist of colouring-matters mixed with 

 a 'vehicle' that is, a liquid which hardens or 

 dries on exposure. Paints are divided into water- 

 colours and oil-colours. In the former, the vehicle 

 is an aqueous solution of gum, and the drying is 

 caused by the evaporation of the water ; in the 

 latter, the vehicle is boiled linseed-oil, and the 

 drying or hardening is caused by the oxidation of 

 the oil (see CHEMISTRY). 



DYEING AND CALICO-PRINTING. 



In order to produce a fast colour upon a fabric 

 made of animal or vegetable fibre (wool, silk, 

 cotton, or linen), it is necessary i. That the 

 colouring-matter, or the materials for producing 

 it, should be presented to the fibre in the liquid 

 state, so that it may soak into the fibre ; 2. That 

 when it has soaked into the fibre it should be 

 rendered insoluble, so as to prevent its being 

 washed out. There are various ways in which an 

 insoluble colour can be produced from solutions 

 of soluble substances i. The solvent maybe re- 

 moved ; 2. The colouring-matter may form an 

 insoluble compound with the substance of the 

 fibre ; 3. Two substances may be separately pre- 

 sented in solution to the fibre, and these two 

 substances may, by acting upon one another, pro- 

 duce an insoluble colour ; 4. A soluble substance 

 may, after its introduction into the fibre, be 

 changed into an insoluble colour by the action of 

 the oxygen of the air. 



We shall give some instances of these different 

 ways of rendering the colouring-matter insoluble. 



I. Removal of the solvent. This method is of 

 very limited applicability. It is obvious that the 

 mere evaporation of water in which the pigment is 

 dissolved is not a case in point, for that would 

 leave the pigment ready to be washed out again. 

 As an instance of a case in which this method 

 is applicable, we may take the dyeing of cloth 

 with an ammoniacal solution of a salt of copper. 

 When the cloth soaked in such a solution is ex- 

 posed to the air, the ammonia evaporates, and 



