=Ammonia-Cochineal.=—This preparation, which is chiefly used by dyers, is obtained by treating cochineal in a well-closed flask with strong ammonia, which dissolves the colouring matter. After about a month alum equal to about 3 per cent. of the amount of cochineal is added without separating the undissolved residue from the solution, and the whole is evaporated at a gentle heat in a tinned pan until it becomes a stiff paste on cooling. The mass solidifies more readily if a small quantity of starch paste is added. ”Cochineal paste” is cochineal which has been treated in this manner; it is generally brought into the market in the form of cakes or small slabs. In addition to the true cochineal other species of the same insect contain a red colouring matter and have a restricted use in dyeing. The most important of these is the Polish cochineal (_Coccus polonicus_), which lives on the roots of the _scleranthus_. It has not been proved that these insects contain the same colouring matter as true cochineal, but it is certain that the colouring matters of Polish and also of Russian cochineal (_Coccus euvæ ursi_) are far inferior in beauty to that of true cochineal. CHAPTER LII. THE COLOURING MATTER OF LAC. From the punctures of the insect _Coccus lacca_ on certain East Indian trees, especially those belonging to the genus _Ficus_, flow at the same time resin and colouring matter in such quantities that the insects are frequently enclosed and large red masses are formed on the trees. The insects live in some measure in these masses, the females lay their eggs in the spaces and the larvæ are said to feed on the red sap contained in the mass. When the larvæ have left the incrustation, generally in November, it is broken off from the branches and collected. It is now known as stick-lac; it consists of large masses of resin of a fine deep red colour. In the interior the cells of the insects may still be perceived. On chewing, it becomes soft and colours the saliva a deep violet. When stick-lac is boiled in water a portion of the colouring matter dissolves. Good stick-lac contains 10 per cent. of colouring matter and 80 per cent. of resin. Seed-lac has the same origin as stick-lac, but frequently the greater part of the colouring matter has been extracted; it rarely contains more than 2·5 per cent., and is consequently of little value for colouring purposes.