Shellac is obtained from the resinous incrustation produced on the bark of the twigs and branches of various tropical trees by the puncture of the female "lac insect" (_Taccardia lacca_). The lac is removed from the twigs by "beating" in water; the woody matter floats to the surface, and the resin sinks to the bottom, and when removed forms what is known as "seed-lac." Formerly, the solution, which contains the colouring matter dissolved from the crude "stick-lac," was evaporated for recovery of the so-called "lac-dye," but the latter is no longer used technically. The seed-lac is bleached by boiling with sodium or potassium carbonate, alum, or borax, and then, if it is not pale enough, is further bleached by exposure to sunlight. It is now dried, melted, and mixed with a certain proportion of rosin or of orpiment (a sulphide of arsenic) according to the purpose for which it is desired. After further operations of melting and straining, the lac is melted and spread into thin sheets to form ordinary shellac, or is melted and dropped on to a smooth surface to form "button-lac." Ordinary shellac almost invariably contains some rosin, but good button-lac is free from this substance. The presence of 5 per cent. of rosin in shellac can be detected by dissolving in a little alcohol, pouring the solution into water, and drying the fine impalpable powder which separates. This powder is extracted with petroleum spirit, and the solution shaken with water containing a trace of copper acetate. If rosin be present, the petroleum spirit will be coloured emerald-green. Borax, soda crystals, and ammonia are all used to dissolve shellac, and it may be asked: Which of these is least injurious to wool? and why? How is their action modified by the presence of dilute sulphuric acid in the wool? I would say that soda crystals and ammonia are alkalis, and if used strong, are sure to do a certain amount of injury to the fibre of wool, and more if used hot than cold. Of the two, the ammonia will have the least effect, especially if dilute, but borax is better than either. The influence of a little sulphuric acid in the wool would be in the direction of neutralising some of the ammonia or soda, and shellac, if dissolved in the alkalis, would be to some extent precipitated on the fibre, unless the alkali, soda or ammonia, were present in sufficient excess to neutralise that sulphuric acid and to leave a sufficient balance to keep the shellac in solution. Borax, which is a borate of soda, would be so acted on by the sulphuric acid that some boric acid would be set free, the sulphuric acid robbing some of that borax of its soda. This boric acid would not be nearly so injurious to wool as carbonate of soda or ammonia would.