This property can be communicated to oils, otherwise suitable, by the addition of a proportion of oleic acid, or by treatment with sulphuric acid, which is afterwards neutralized or otherwise removed. Oil mordants are applied to the yarn or cloth in the cold by means of padding, the goods being then spread out to the air. This alternate process is repeated several times.
The following method has been recently adopted for preparing au oil mordant for dyeing with alizarinc. Take 3000 parts of castor-oil and pour into it, in a thin stream, and with continual stirring, 650 parts oil of vitriol, in such a manner that the process of mixture may last for 3 hours, and that no rise of temperature may take place. The mixture is then left to stand for 12 hours, and is next diluted with 3500 parts of water. Then about 650 parts soda-ash, more or less according to its strength, is added by small portions at a time, till the liquid uo longer reddens blue litmus-paper. In this state, it forms a white emulsion, if shaken up with water. If it is desired to avoid this property, ammonia is added by degrees, till a portion of the mixture drawn out dissolves in distilled water, without causing any turbidity. It is then allowed to settle, and after standing for 12 hours, the oil may be drawn off for use. A deposit of crystals of sulphate of soda remains at the bottom of the vat. The product obtained is a sulphoricinoleate of ammonia.
A more complicated process has been patented by Dr. A. Muller-Jacobs, who proceeds as follows :—He heats castor-oil with s its weight of oil of vitriol, poured in as a slender stream. This part of the process is conducted in lead-Hued iron tanks, traversed by coils of lead piping, in which, if needful, ice-cold water can be made to circulate, to prevent heating. After standing for 2-3 hours, the mass is diluted with water, and neutralized with a lukewarm solution of soda (28 lb. soda crystals to every 10 lb. acid which has been used). This alkaline solution is added very slowly, and with constant stirring. The liquid is then allowed to stand and the next morning it is
found separated from the saline mother-liquid, and is drawn off for use.
Meantime pyroterebate of soda is prepared by boiling in an enamelled iron vessel 100 parts rosin with 250 parts nitric acid, the rosin being added gradually, and in powder. After hour, the mass is gradually evaporated, and the residue is heated for hour to 200°-311° (392°-522° F.) in a closed iron vessel. When cold, it is heated with 20-30 per cent. of its weight of oil of vitriol ; then, after the lapse of 2-3 hours, neutralized with soda, and the sulphopyroterebate of soda is reserved for use.
To make the oil mordant, equal measures of the sulphoricinoleate and of the sulphopyroterebato are mixed, and are at once fit for use.
The applications of oil mordants, both in dyeing and printing, will be found capable of further development. Various attempts have been made to use oils as a medium for the fixation of pigments in printing. The difficulty to be overcome is the tendency of the oil to spread in the fibre. This is to be prevented, without interfering with its transparency, or darkening its colour. O'Neill has obtained very satisfactory results on a small scale, but by processes which he considers too delicate and costly for actual practice.
Soaps are not unfrequently employed for fixing artificial colours upon the fibre, but almost invariably in conjunction with ordinary mordants, such as alum, red liquor, or compounds of tin and lead. In such cases, the result is that a compound of alumina, lead, or tin, with the fatty acids of the soap—in other words, an insoluble metallic soap—is deposited upon the fibre.
Mordants at the best must be regarded as necessary evils. One of the greatest triumphs of tinctorial chemistry would be the production of A complete scale of substantive colours, available on every kind of fibre. Many steps have already been taken in this direction. W. C.
(See Acid [Acetic]—Iron, Acetates of ; Albumen ; Alum ; Alumina; Dyeing and Calico printing.)