Hence, however, it is very necessary that the dyer should have a competent knowledge of chemistry and drugs, that he may be able to judge of the goodness of the articles which he uses, and of the numerous and extraordinary combinations into which they enter. To _chemistry_, in particular, every able and scientific dyer must be largely indebted; for this reason it is that we have endeavoured, in this _introductory chapter_, to sketch some of the most important facts in this universal and interesting science. In possession of these qualifications, and working upon the above plan, the dyer can never be far from the desired result in all his processes. His deviations, if any, will be few, as from his knowledge, he will soon perceive the first approach of any incorrectness, and be able to adjust it generally without much inconvenience. The _chemical terms_ now introduced into treatises on dyeing are chiefly taken from the Greek language, and are used in such a manner as to convey, by their etymology, an idea of the nature of the substances to which they are applied. _Oxygen_ implies the producer of acid: _hydrogen_, the producer of _water_; _nitrogen_, the producer of _nitre_, &c. The term _gas_ has been explained above. _Caloric_ is a term used by chemists for heat; but caloric is used in a more extensive signification than the term heat, thus: although a gas might possess no sensible heat, yet being in a gaseous state, it is assumed to contain a certain portion of caloric which keeps it in its gaseous state; the same observation will apply to liquids whether aqueous, oleous, or metallic. _All the measures mentioned in this work unless otherwise described, are those usually called in this country_ WINE MEASURE, _and not those which have been introduced by a late act of parliament_, _called_ IMPERIAL MEASURES. [2] Cochineal was at first supposed to be a _grain_, which name it still retains by way of eminence among dyers. URE. [3] For the cultivation of Woad in England, see Parish's paper in vol. xii. of the Bath Society's Report, or Tilloch's Mag. vol. xxxviii. [4] What are called _iron moulds_ in cotton, linen, &c. are, it is well known, nothing but the marks of a _buff_ colour, usually left by ink and other matters which contain iron: acids, of course, dissolve, and discharge these buff colours; the _oxalic acid_ does so without decomposing the cloth. [5] "_Acetate of Alumina_ is now most frequently made for the Calico-Printers by dissolving alum in a solution of crude acetate of lime, (pyrolignite); a gallon of the acetate, of specific gravity, 1.050 or 1.060, being used with two pounds and three-quarters of alum. A sulphate of lime is formed, which precipitates, while an acetate of alumina mixed with some alum floats above. The acetate of alumina employed as a mordant for chintz, is still commonly made by the mutual decomposition of alum and acetate of lead."—_Ure's Berthollet_, vol. ii. p. 331. [6] Berthollet. CHAPTER II.