3.—Green Dyes.
Heat a sample of the paper in dilute spirit. If the spirit acquires no colour, warm for a short time with dilute sulphuric acid. If both paper and solution become brownish red, we have logwood plus fustic. If this fails, boil with concentrated hydrochloric acid. A yellow solution shows green earth. If this fails, boil with concentrated caustic soda. Browning shows chrome green. If the spirit becomes blue, it is a case of paper which has been topped with blue on a yellow, brown, or green ground. The solution and the insoluble part are separately tested. The case is probably one of an aniline blue dyed over a mineral pigment. If the spirit becomes green, heat with dilute hydrochloric acid. If the fibre is completely or nearly bleached, and the acid turns yellow, the dye is brilliant green, malachite green, or one of their allies.