The practice of flour bleaching originated in this country about ten years ago; bleaching, however, is said to have been attempted in France two or three years prior to this. The practice was rapidly adopted by millers in the United Kingdom, in America, and elsewhere. Such bleaching is applied only to roller-milled flour. Numerous patents have been granted for bleaching appliances and for the application of various chemicals to the bleaching of flour. Ozone, chlorine, oxides of chlorine, bromine, nitrogen peroxide and other oxidising substances have been suggested and tried as bleaching agents. Of these substances nitrogen peroxide is the only one which has given satisfactory results, and all commercial bleaching of flour at the present time depends on the use of this substance. It can be produced in various ways and from a variety of materials. Two methods of production, which may convniently be termed the chemical and electrical methods, are in use commercially at the present time. In the first of these nitrogen peroxide is produced by the action of nitric acid on ferrous sulphate, the amount of gas formed being controlled by regulating the supply of acid and ferrous sulphate. A current of air charged with the gas is led through a revolving reel or “agitator” as it is called, through which a stream of flour is continually flowing. The flour in its passage is throughly exposed to the action of the nitrogen peroxide, and is bleached when it emerges from the agitator. In actual practice this process possesses certain commercial disadvantages. The apparatus requires constant attention if the degree of bleaching is to be properly controlled; overbleaching and condensation of acid resulting in local staining of the flour are liable to occur, while in the hands of ordinary workmen the use of strong acids is not entirely free from risk. As regards expense, it compares unfavourably with other methods, some of which are said to be worked at one-tenth of the cost of the acid process.