[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.
More recently, the use of organic salts of thorium and cerium for impregnation has been proposed by Dr. F. W. Wirth;[550] in fixing the impregnated fabric with hydrogen peroxide, the cerium is not removed in solution, since the weak organic acid formed will not dissolve cerium peroxide. The same author has also suggested[551] the addition to the fixing bath of substances which absorb oxygen from the air—e.g. sodium hydrogen sulphite, resorcinol, tannin—to prevent removal of cerium. He has also advocated impregnation with amorphous salts,[552] which will obviate the necessity for any subsequent fixing treatment, the hypophosphites and double compounds with ammonium oxalate being specified. Attempts have been made to achieve the same end by other methods. Thus Silbermann[553] has proposed a preliminary treatment with alkalies (mercerisation); the fabric is treated with concentrated sodium hydroxide solution in absence of air for half an hour, pressed through rollers, and plunged into the impregnating solution. Two years previously a patent was taken out by Drossbach[554] to protect the use of colloidal solutions of the hydroxides. To a boiling suspension of well-washed, freshly-precipitated thorium hydroxide, a solution of a small quantity of the nitrate is gradually added; after half an hour a colloidal solution is obtained, which, after the addition of the required quantity of cerium nitrate, and dilution to a suitable extent, is employed directly for impregnation. The patent states that this solution is more readily absorbed than the ordinary nitrate solution, but the statement has been questioned.
[550] Chem. Zeitg. 1911, 35, 752.
[551] Zeitsch. angew. Chem. 1912, 25, 922.
[552] Chem. Zeitg. 1911, 35, 752.