The determination of soluble silica and alumina (as silicate and aluminate of soda), of sulphuric acid (as sulphate of soda), of chlorine (as eommon salt), and of other mineral constituents of soap, must be made in the acid solution that remains after decomposing the soap with a suitable mineral acid ; the estimation of carbonic acid (as carbonate of soda)presents great difficulties. The ordinary methods of inorganic quantitative analysis may be applied in these cases.
Substances Insoluble in Water.—Iu properly-made unadulterated soap, these should only consist of colouring matters and mottling. To estimate their amount, dissolve a known weight in water, deeant the clear liquid, collect the deposit on a tared filter, wash, dry, and weigh. Organic impurities may be estimated by igniting this residue, and weighing again, when only mineral impurities remain. Starch or farina is deteeted hy iodine ; mineral impurities, by the ordinary methods of mineral analysis.
Two or three examples of freshly-made analyses of hard soap are here given ; no deduction is made for water combined with the fatty acids (p. 1794).
A few remarks upon tbe location, prospects, legislative condition, and other general considera tions connected with the soap-trade, may fitly close this portion of the article.
This industi y is by no means localized in any one part of the British Islands ; but, although the total amount of soap made in England is probably greater now than it ever was, the tendency of the last 25 years has been in the direction of concentrating the manufacture in the hands of a few firma. Among these, may be mentioned, W. Gossage & Sons, Widnes, Lancashire; J(v. Crosfield & Sons, Warrington ; Hodgson & Simpson, Wakefield ; Cook & Sons, Anderson & Cattley, and Cowan & Sons, all of London ; Chrietopher Thomag & Bros., and Lawson, Phillips, & Billings, both of Bristol ; Tennant, of Glasgow ; Hedley & Sons, Newcastle-on-Tyne ; and others. Probably the eldeNt ,oap-works in the country are, or at any rate until recently were, to be found in Bristol, which still retains great reputation for its soap. A relic of this may be found at the present day in Holland, in some parts of which no soap can be sold which is not stamped with the word BRISTOL, Of the two soap-works mentioned as now left in that city, the former, belonging to Christopher Thomas & Bros., was established in 1745.
The abolition of the duty on soap in 1853, then about 2d. a lb., and producing a revenue of upwards of I,000,000/., naturally gave an immense impulse to improvements io the manufacture, and various valuable patents were very shortly taken out, the most important of which were those of W. Gossage for silicated soaps, that of T. Thomas for cheap detergent soaps made from mixtures
of neat soap, silicate of soda, and sulphate of soda, that of Blake & Maxwell for hydrated soaps (p. 1777), and those of C. N. Kottula, for various improvements in the making of blue-mottled and other soaps. An association of soap-manufacturers in England holds quarterly meetings, at which prices are revised, common action agreed upon, and legislative enactments affecting the trade dis cussed and watched. All soap-factories, in coinmon with other factories, are subject to inspection by Factory Inspectors acting under the Government, and to the visits of a Certifying Surg,eon. In a well-managed soap-works, the sources of nuisance are very slight, and comparatively inoffensive; most of them arise, not from tha actual process of soap-making itself, but from tbe preliminary opemtions of refining, purifying, and bleaching tha fatty matters employed (sec Oils, p. 1448, and pp. 1458-1462). They may all be obviated by conducting such operations in closed vessels provided with trunks communicating with the draught of a flue; when impure and rancid fats are used direct for soap-making, the copper should be provided with a cover and a similar trunk. In default of a flue-draught, a fan, or a jet of steam, may be used to oreata a good current of air.
Since the removal of the duty, there are few means of fortuing an estimate of tho oxtent of the soap-trade in England; it is known, however, that many of the larger houses mako much more than 5000 tons a year, while a few make over 10,000, and it is stated that coo house is capable of turning out 500 tons in a week whan necessary.
The total annual production in the United Kingdom was estimated at 250,000 tons by Prof. Roscoe, iu his inaugural address as President of the Society of Chemical Industry, in June 1881. Oar exports of soap in 1880 wore as follows :—To the British W. Indies and British Guiana, 69,527 cwt., 71,302/. ; British S. Africa, 66,563 cwt., 72.928/. ; Java, 34,0 l3 cwt., 31,510/. ; China, 30,420 owt., 28,472/. ; Spain and Canaries, 24,430 cwt., 24,520/. ; Portugal, Azores, and Madeira, 23,289 owt., 24,949/. ; Gibraltar, 14,897 cwt., 15,455/. ; Italy, 11.883 cwt., 14,442/. ; foreign NV. Africa, 10,962 owt., 10,572/. ; Bombay and Sind, 10,928 ect., 11,95G/.; Bengal and Burma, 10,765 cwt., 16,098/. ; foreign W. Indies, 10,170 owt., 10,798/. ; Australia, 7287 cwt., 13,433/. ; Hong Kong, 7158 owt., 8334/. ; Holland, 5674 cwt., 5617/. ; Channel Islands, 4328 cwt., 6868/. ; British N. America, 3513 cwt., 4925/.; France, 1842 owt., 4598/. ; other countries, 41,159 cwt., 60,509/. ; total, 391,808 ewt., 440,286/.