Greens and blues with a copper basis

Starch may be detected by heating the substance with water, filtering, and testing the cooled liquid with tincture of iodine. 

Two groups may be distinguished, according as arsenic is present or absent. 

Of the arsenic-free pigments the best known are Mountain green and blue (basic copper carbonates) and Bremen green and blue (copper hydroxides) use is made, but less commonly, of greens based on the basic acetate, basic sulphate, oxychloride and stannate of copper, already mentioned. All these products may be adulterated with the usual extraneous white substances, such mixtures being given special names. 

Examination of these products comprises firstly the technical tests relating to intensity, fastness and behaviour in mixtures, and further, qualitative analysis for the determination of the nature of the product and of any adulterations, and also certain quantitative determinations. The qualitative investigation is carried out as in paragraph 1 and the quantitative determinations as in paragraphs 2 and 3 

Qualitative Examination.—A little of the substance is heated to redness in a test-tube emission of a garlic-like odour and formation of a white sublimate indicate arsenic, whereas if the substance blackens without giving such odour or sublimate, arsenic is absent. 

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