A rather similar proposal[541] substitutes for ammonia an alkaline solution of hydrogen peroxide, obtained by dissolving sodium peroxide in water. After saturation for a minute or so, the fabric is wrung out and dried, there being no necessity, according to the patent, for any subsequent washing. The same company in an earlier patent[542] suggest a fixing bath of ‘an alkali or amine with an acid which can form insoluble basic double salts with the earth metals,’ the said salt to be precipitated on the fibre, whilst an alkali or amine nitrate goes into solution; acetic and benzoic acids and phenol are mentioned. Apparently this process did not give satisfactory results. The same may be said of the hypochlorite method of Visseaux.[543] Equally interesting, and doubtless equally practical is the proposal[544] to treat the dried impregnated mantle with ozone in a closed chamber, which possibly inspired the even more original suggestion[545] that the fabric be first washed in ozonised water, dried, then impregnated and dried, and finally treated with ozone. According to yet another French patent,[546] the impregnated and dried fabric is to be treated with an alcoholic solution of hydrofluoric acid, which will give a viscous insoluble mixture of thorium and cerium fluorides in the fabric, and at the same time will remove any impurities. Another patent[547] proposes the use of hydrazine and similar bases, cerium nitrate being added to the fixing solution. [541] _D._ 247940, June, 1912; _F._ 430417, August, 1911. [542] _F._ 403433, September, 1909, Bruno Co. [543] _F._ 408807, February, 1910. [544] _F._ 414700, June, 1910. [545] _F._ 422643, January, 1911. [546] _F._ 426156, April, 1911. [547] _E._ 11904, 1909. Innumerable suggestions have been made for fixing by means of ammonia gas, or vapours of organic bases.[548] An English patent granted in February 1910[549] protects ‘various improvements,’ which consist in carrying out a preliminary treatment with steam, impregnation with the solution of nitrates, conversion of nitrates into oxides either by steam carrying ammonia, pyridine, etc., or by the action of these vapours without steam in a vacuum, all in one chamber, which can be exhausted or filled with various solutions or vapours as required. [548] _Vide_, _e.g._ _D. R. P._ 199615 of June, 1908. [549] _E._ 25549, 1908.