=Natural Green= is a mixture of Guignet’s green with picric acid; it is used in making artificial flowers instead of emerald green. =Non-arsenical Green= was proposed as a substitute for emerald green, which, however, it does not equal in brilliance. It is obtained by mixing copper blue (basic copper carbonate) with chrome yellow, chalk and ferric oxide, in somewhat variable proportions. It usually contains 80 to 82 per cent. of the copper compound and 13 to 15 per cent. of chrome yellow. * * * * * In making mixtures of pigments it is to be remembered that chemical actions may occur in the mixture; colours which act upon one another should not be mixed: the mixture would contain the cause of its own destruction. For example, a lead pigment should not be mixed with one containing sulphur in the form of a sulphide or sulphate. By following this important rule the number of pigments which may be mixed together is considerably diminished; the advantage is that durable colours are produced, which do not change in a short time to an unrecognisable shade. CHAPTER XXXVI. VIOLET MINERAL PIGMENTS. =Chromic Chloride.=—The violet modification of chromic chloride is a compound which is little used, but deserves the highest attention on account of its durability and beauty of shade. Up to the present chromic chloride has been almost exclusively used for colouring paper hangings under the name of chrome bronze, which it has received in consequence of its property of imparting a peculiar metallic lustre to paper upon which it is rubbed. It is also possible to fix this substance upon fabrics, which thus acquire a similar metallic lustre. Pure chromic chloride forms beautiful peach-blossom coloured scales, which can only be obtained by treating chromium oxide in a certain manner with chlorine. The pure substance is practically insoluble in water, but if the water contains but a trace of chromous chloride the chromic chloride readily dissolves to a green solution. In the preparation of this compound it is necessary to avoid the least trace of chromous chloride, otherwise the product will begin to change when it comes into contact with moist air.