Manufacture of hard soaps

Until the beginning of the nineteenth century the soda required for the manufacture of hard soap was obtained either from kelp (seaweed ash) or barilla, a plant ash mostly imported from Spain or the South of France. The alkali content of barilla was very variable. Parkes found that the best Spanish kinds contained from 10 to 20 p.c. of Na20 (one, exceptionally, 30 p.c.) kelp contained only i to 8 p.c. Stahl knew that the base of common salt was soda (see Vol. II, p. 681), and during the eighteenth century many attempts were made to obtain soda from common salt. The most promising approach was to convert the salt into sodium sulphate by heating with sulphuric acid. 

Materials,—The materials used in the manufacture of soap, are the various kinds of oil or fat, resin, and the alkalies, potassa and soda. All oils and fats of whatever kind, vegetal or animal, yield soaps, when treated with alkali, as will he subsequently described. Only a very limited number, however, is used in thiB manufacture and these such as may be obtained at a very low price compared with that of the others. In Great Britain palm-oil is probably consumed in greater quantity than any other, and principally in the production of hard soap for soft soaps, the various kiuds of fish-oils, the drying oils from seeds, and tallow are mostly employed. 

The chief uses of soda are in the manufacture of glass and of hard soap. The carbonate is used in washing, and is a powerful detergent, although milder than carbonate of potash. 

The alkali employed in the manufacture of soft soaps is potash, and it is a characteristic of all soaps made with this alkaH that, instead of assuming a hard, solid con sistence, as is the case with soaps made om soda, they are always soft, tenacious, and more or less transparent. Moreover, potash soaps always contain a large percentage of water, more in a state of mechanical mixture than m chemical combination and while 3 parts of fatty matter will generally yield about 6 parts of soda soap, the same proportion of fatty matter, treated with caustic potash ley, will yield from 6 to 7 parts of potash soap. 

Water softener manufacturers remind us of the many undesirable effects produced by hard water. Besides enhancing the likelihood of harmful scale deposits in plumbing, water heaters, and dishwashers, hard water also has been associated with bathtub scum, deposits on laundry, scale on glasses and dishes, scratchy skin, and unmanageable hair. A simple chemical process explains the origin of hard water. Additional chemical reactions provide an explanation for the scum and deposits that readily form when soap and hard water combine. 

Soap and detergent manufacture and formulation plants are situated in many areas in the United States and other countries. At most, if not all of these locations, the wastewaters from production and cleanup activities are discharged to municipal sewer systems and treated together with domestic, commercial, institutional, and other industrial wastewaters. Following the precipitous reduction in production and use of hard surfactants such as ABS, no discernible problems in... 

Marseilles Soap.—This variety of soap is produced by the saponification of olive oil alone. The process does not materially differ from that described for white soap. Tho duration of the operation is longer or shorter according to the quality of the oil. Some manufacturers use, in the fabrication of this soap, a certain proportion of poppy oil with the olive oil and the addition is rather beneficial than otherwise, as the soap produced is less hard, and consequently more easily applicable to detergent purposes. It is at present manufactured on a considerable scale in this country. 

Soft Soap.—This variety of soap differs in many essential particulars from those already described. The alkali need in its production is potassa exclusively, and the oil, either in whole or in part, a drying oil, as that of hemp seed, popples, et cetera, or fish oil, as whale or seal oil. The theory of the reaction of potassa upon fateand oils is precisely the same as in the case of soda. Soaps with potassa base are, however, manufactured on an entirely different system to those of soda or hard soaps. In tbe latter, the soap is withdrawn from the lio when only a portion of the ojl lias been sapomfiod, and fresh lies are added nntil saponification is complete. 

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