Hard Soap

Uses of the alkali hydroxides.—A soln. of potassium hydroxide is used in the laboratory as an absorbent for carbon dioxide, the sodium compound is not so often used because of the formation of less soluble sodium carbonate which is liable to choke the delivery tubes with crystals. Potassium hydroxide is used in making soft soaps the corresponding sodium compound gives the ordinary hard soaps. The hydroxide fused with a little lime is used as a cautery—pierre a cautere. The alkali lye is also used as a cleansing fluid, since it forms soluble soaps with many greases and fats. The lye also dissolves animal tissues. 

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. 

Nevertheless, much room remains for future investigators in this wide field and many improvements may still be expected from further research. Tallow, olive, palm, and cocoa-nut oils, oleic acid, and resin are used for the production of hard soaps fish and seed oils, on the contrary, for soft soaps. The mixture of oleic acid with amall quantities of stearic and margaric acids, which is obtained in the separation of steario acid by pressure, as desoiibod under the artlola Candle, affords an excellent soap, the production of which is a secondary... 

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 In tbe latter, the soap is withdrawn from the lio when only a portion of the ojl lias been sapomfiod, and fresh lies are added nntil saponification is complete. 

In Germany, America, and some other countries, soda and potassa are frequently both used in tho production of hard soap. The-determination of the amount of alkali in sucli instances is much less easily performed. The most convenient process is as fellows —A hundred grains of the Boap are taken and dissolved in water, as before, and the solution is oxactly neutralized by means of the soda test acid. By a simple calcula-... 

When triglycerides are boiled up with alkali, the esters are hydrolysed and a mixture of carboxy-late salts and glycerol is formed. This was how soap was made—hard soap was the sodium salt and soft soap the potassium salt. 

Both animal and vegetable oils are used in the manufacture of soap and candles. When fats and oils —such as tallow, palm oil, olive oil—-.are boiled in large east iron pans with caustic alkali, they become decomposed and yield an alkaline salt of the fatty acid—soap and glycerine. The excess of alkali and the glycerine are separated by the addition of a solution of common salt the soap, being insoluble in the brine, rises to the top, and is ladled out as a granular curdy mass, run off into frames—boxes—to cool and solidify. Hard soaps, shell as curd and yellow soap, are compounds... 

Hard soap Soao, the base of which is sodium hydroxide. 

Salt Bheum Ointment. Mix in an earthen vessel, 1 ounce oqua-fortis, with 1 ounce quicksilver when effervescence has ceased, incorporate with it 1 pound lord and 1 ounce dissolved hard soap then work into the mixture 1 ounce prepared chalk and 4 table-spoonful spirits of turpentine. 

Cl and Br under ordinary pressure attack oleic acid with formation of products of substitution. If oleic acid be heated with an excess of caustic potassa to 200° (392° F.), it is decomposed into palmitic and acetic acids CisHjiOi -I- 2KHO = CuHnOjK -i-CjHsOjK -1- Hj a reaction which is utilized industrially to obtain hard soaps, palmitates, from olein, which itself only forms soft soaps. Cold HjSOi dissolves oleic acid, and deposits it unaltered... 

Hard soaps consist essentially of the sodium salts of palmitic, stearic and oleic acids. As the calcium and magnesium salts of these acids are insoluble in water, soap does not immediately pass into solution and form a lather with hard water. The soap dissolved reacts with the metallic salts in solution and the corresponding salts of the fatty acids are precipitated. This process continues until all the metals which form insoluble soaps are precipitated. The reaction which takes place is illustrated by that between sodium palmi-tate and calcium chloride —... 

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. 

Mode of Preparation.—Olive oil is boiled with caustic soda (sodium hydrate) glycerin passes into solution, and sodium oleate (hard soap) floats on the surface of the liquid. After remaining quiescent for a few hours the soap [is skimmed off, transferred to frames, in which it solidifies on cooling, and finally cut by wires into slabs or bars. 

Although the British Pharmacopoeia directs hard soap to be made from olive oil, the best curd soap of commerce, which is a mixture of sodium stearate, palmitate, and oleate, and which is prepared from various solid and liquid fats, may be substituted for it in practice. 

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