#Bleaching Wool by Peroxide of Hydrogen.#--During recent years there has come into use for bleaching the animal fibres peroxide of hydrogen, or, as the French call it, oxygenated water. This body is a near relation to water, being composed of the same two elements, oxygen and hydrogen; in different proportions in water these elements are combined in the proportion of 1 part of hydrogen to 8 parts of oxygen, while in the peroxide the proportions are 1 of hydrogen to 16 of oxygen. These proportions are by weight, and are expressed by the chemical formulae for water H_{2}O, and for hydrogen peroxide H_{2}O_{2}. Water, as is well known, is a very stable body, and although it can be decomposed, yet it requires some considerable power to effect it. Now the extra quantity of oxygen which may be considered to have been introduced into water to convert it into peroxide has also introduced an element of instability, the extra quantity of oxygen being ever ready to combine with some other body for which it has a greater affinity than for the water. This property can be utilised in the bleaching industry with great advantage, true bleaching being essentially a process of oxidation. The colouring matter of the fibre, which has to be destroyed so that the fibre shall appear white, is best destroyed by oxidation, but the process must not be carried out too strongly, otherwise the oxidation will not be confined to the colouring matter, but will extend to the fibre itself and disintegrate it, with the result that the fibre will become tendered and be rendered useless. Peroxide of hydrogen is a weak oxidiser, and therefore, although (p. 035) strong enough to destroy the colouring matter of the fibre is not strong enough to decompose the fibre itself. Hydrogen peroxide is sold as a water-white liquid, without any odour or taste. Its strength is measured by the quantity of oxygen which is evolved when one volume of the liquid is treated with potassium permanganate; the most common strength is 10 volume peroxide, but 30 and 40 volume peroxide is made. On keeping it loses its oxygen, so that it is always advisable to use a supply up as quickly as possible.