To the perfume formulae given above, may now be added : Bose Soap.-4 oz. oil of rose geranium, Harsh-mallow Soap.-6 oz. oil of lavender, 2 bergamot, 4 1 em on- grass.
1 rose, peppermint, 1 cinnamon. petit-grain.
The finest qualities of toilet soaps, however, require a great deal of manipulation by costly machinery, which has been chiefly devised by the French, although the Americans, with their well-known mechanical ingenuity, have recently constructed equally good machines. The basis of these soaps, or " stock " as it is technically termed, is usually made by the cold process, from the purest possible tallow, lard, &c., with little if any coco-nut-oil, which, if used, should be the Cochin variety. All the colouring matter, perfume, and other ingredients, are incorporated with tbe soap under hydraulic pressure, at the ordinary atmospheric temperature ; hence the most dedicate essences can be employed, even those that are extracted in the cold from plants. The first operation is to " strip " the stock-soap, i. a. to cut it up into strips or shavings; this may be done with a plane by hand, or by a machine (Fig.
1274), whose essential parts are a revolving wheel A, upon which are set 4 or 6 knives, aud a hopper F to contain the bars. After stripping, the soap is frequently dried some what, and it is then passed through the mill several times, while the colour, perfume, &c., are here added to it. The mill, which is shown in Figs. 1275-6, consists essentially of three cylindrical contiguous rollers B, by whose action the soaps, colour, perfume, &c., after repeatedly running through, are blended into a thick homogeneous paste. When this has been effected, the soap is ready for the final operation, known as " plotting " (from the French, pelotage), in which the paste is sub jected to enormous pressure, sometimes 3000-4000 lb. a sq. in., to form it into cakes, or into con tinuous bars from which cakes may be cut. Such a machine, known as Rutschman's hydraulic soap-plotting machine, made in Philadelphia, is shown in Fi4 1277. It may be charged 5 times in a. working day, and will " plot " 200 lb. at each operation. It is better to let each separate cake be " plotted " by this machine, hut if bars are made, and the cakes subsequently stamped, a Powerful stan3ping-press must be employed. Cakes made in this way, are not liable to crack in use, as those made by tho other two procemes are ; before being packed, they are not nnfrequently dried, and almost always polished. This may be done by hand with a cloth moistened with alcohol, or, according to Dupuis, by momentary exposure to a current of steam, which, if desired, may be previously passed through a cloth impregnated with any fragrant odour ; it is said that no other method gives such a beautiful, even, and lustrous coating.
A few hints on colour, and formulte for perfume, are here given. Whenever it is desired to produce a mottled or marbled appeamnce in the soap, an insoluble colour rawat be employed ; but whenever a uniform tint is required, preference should be given, whenever possible, to colours soluble in either water or alcohol, a condition fulfilled by numerous coal-tar colours. Care should be taken to ohoose those that are permanent, and unaffected by strong alkali. Salts of chromio acid should be avoided, since they aro apt to turn green by transfirenee of some of their oxygen to the fatty matter of the soap ; the borate of chromium, known as " Guignet's green," is very stable, and so are ultramarine and vermilion. The finest yellow is produced by infusion of saffron. The resources of the dyer's art are constantly producing new tints, whose properties in relation to soap must he ascertained by that best of all tests, experiment.
_ _ _ _ Transparent Soaps.The peculiar appearance of these soaps is due to the use of alcohol in their fabrication, and it may be applied in two ways. The older method, still employed, is to cut up ordinary soap into shavings, to dry these in heated air, and to dissolve them in half their weight of alcohol of 95°, in a suitable closed vessel provided with a head and condensing-worm, and heated by steam or a water-bath ; when the soap is dissolved, and the excess of alcohol evaporated, the soap is drawn off, perfumed, and allowed to cool. Transparent soaps are now, however, usually made by the cold process, but to ensure success, very great exactitude in the proportions of the materials used is necessary, as well as much experience and skill. The fatty matters em ployed are tallow, coco-nut-oil, lard, castor-oil, and olive-oil, in varying proportions, but all of the purest quality. For 100 parts by weight of fatty matter, 45 parts caustic soda leys at 40° B., and 50-55 parts of alcohol of 95° should be used. One half the leys should be stirred into the melted fat, the temperature of the mixture not exceeding 49° (120° F.), and when thoroughly incorporated the remainder of the leys, mixed with the alcohol, should be added ; saponification will take place rapidly, and the perfume should now be added, and the whole cooled very gradually in frames; 20 parts glycerine added to the above -will make a good transparent glycerine-soap ; occasionally some clear syrup of white sugar is added also. These soaps are seldom coloured, but any colour used in them should be quite transparent ; it will be noticed that they do not become quite trans parent until they have been exposed to the air for some days.