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RAW MATERIALS USED IN SOAP MAKING 1-30

CONSTRUCTION AND EQUIPMENT OF A SOAP PLANT 31-34

CLASSIFICATION OF SOAP MAKING METHODS 35-46

CLASSIFICATION OF SOAPS 47-104

GLYCERINE RECOVERY 105-126

ANALYTICAL METHODS 127-164

STANDARD METHODS FOR THE SAMPLING AND ANALYSIS OF COMMERCIAL FATS AND OILS 165-195

Appendix 219-237

Useful Tables

Index 239

Raw Materials Used in Soap Making.

Soap is ordinarily thought of as the common cleansing agent well known to everyone. In a general and strictly chemical sense this term is applied to the salts of the non-volatile fatty acids. These salts are not only those formed by the alkali metals, sodium and potassium, but also those formed by the heavy metals and alkaline earths. Thus we have the insoluble soaps of lime and magnesia formed when we attempt to wash in "hard water"; again aluminum soaps are used extensively in polishing materials and to thicken lubricating oils; ammonia or "benzine" soaps are employed among the dry cleaners. Commonly, however, when we speak of soap we limit it to the sodium or potassium salt of a higher fatty acid.

It is very generally known that soap is made by combining a fat or oil with a water solution of sodium hydroxide , or potassium hydroxide . Sodium soaps are always harder than potassium soaps, provided the same fat or oil is used in both cases.

The detergent properties of soap are due to the fact that it acts as an alkali regulator, that is, when water comes into contact with soap, it undergoes what is called hydrolytic dissociation. This means that it is broken down by water into other substances. Just what these substances are is subject to controversy, though it is presumed caustic alkali and the acid alkali salt of the fatty acids are formed.

OILS AND FATS.

Inasmuch as a soap is the alkali salt of a fatty acid, the oil or fat from which soap is made must have as a constituent part, these fatty acids. Hydrocarbon oils or paraffines, included in the term "oil," are thus useless in the process of soap-making, as far as entering into chemical combination with the caustic alkalis is concerned. The oils and fats which form soap are those which are a combination of fatty acids and glycerine, the glycerine being obtained as a by-product to the soap-making industry.

NATURE OF A FAT OR OIL USED IN SOAP MANUFACTURE.

Glycerine plus 3 Fatty Alcohols equals Fat or Oil plus 3 Water.

SAPONIFICATION DEFINED.

When a fat or oil enters into chemical combination with one of the caustic hydrates in the presence of water, the process is called "saponification" and the new compounds formed are soap and glycerine, thus:

Fat or Oil plus 3 Sodium Hydrate equals Glycerine plus 3 Soap.

It is by this reaction almost all of the soap used today is made.

FATS AND OILS USED IN SOAP MANUFACTURE.

The various and most important oils and fats used in the manufacture of soap are, tallow, cocoanut oil, palm oil, olive oil, poppy oil, sesame oil, soya bean oil, cotton-seed oil, corn oil and the various greases. Besides these the fatty acids, stearic, red oil are more or less extensively used. These oils, fats and fatty acids, while they vary from time to time and to some extent as to their color, odor and consistency, can readily be distinguished by various physical and chemical constants.

Much can be learned by one, who through continued acquaintance with these oils has thoroughly familiarized himself with the indications of a good or bad oil, by taste, smell, feel and appearance. It is, however, not well for the manufacturer in purchasing to depend entirely upon these simpler tests. Since he is interested in the yield of glycerine, the largest possible yield of soap per pound of soap stock and the general body and appearance of the finished product, the chemical tests upon which these depend should be made. Those especially important are the acid value, percentage unsaponifiable matter and titer test.

A short description of the various oils and fats mentioned is sufficient for their use in the soap industry.

In the manufacture of soaps for toilet purposes, it is usually necessary to produce as white a product as possible. In order to do this it often is necessary to bleach the tallow before saponification. The method usually employed is the Fuller's Earth process.

FULLER'S EARTH PROCESS FOR BLEACHING TALLOW.

The tallow in the bleaching tank is heated to 180? F. and ten pounds of dry salt per ton of fat used added and thoroughly mixed by agitation. This addition coagulates any albumen and dehydrates the fat. The whole mass is allowed to settle over night where possible, or for at least five hours. Any brine which has separated is drawn off from the bottom and the temperature of the fat is then raised to 160? F. .

Five per cent. of the weight of the tallow operated upon, of dry Fuller's earth is now added and the whole mass agitated from twenty to thirty minutes.

The new bleached fat, containing the Fuller's earth is pumped directly to a previously heated filter press and the issuing clear oil run directly to the soap kettle.

Saturated brine is then added to salt out the soap, the Fuller's earth is allowed to settle to the bottom of the tank and the soap which solidifies after a short time is skimmed off to be used in a cheap soap where color is not important. The liquor underneath may also be run off without disturbing the sediment to be used in graining a similar cheap soap. The waste Fuller's earth contains about 0.1 to 0.3 per cent. of fat.

METHOD FOR FURTHER IMPROVEMENT OF COLOR.

A further improvement of the color of the tallow may be obtained by freeing it from a portion of its free fatty acids, either with or without previous Fuller's earth bleaching.

To carry out this process the melted fat is allowed to settle and as much water as possible taken off. The temperature is then raised to 160? F. with dry steam and enough saturated solution of soda ash added to remove 0.5 per cent. of the free fatty acids, while agitating the mass thoroughly mechanically or by air. The agitation is continued ten minutes, the whole allowed to settle for two hours and the foots drawn off. The soap thus formed entangles a large proportion of the impurities of the fat.

VEGETABLE OILS.

The oil is found in the market under three different grades: Cochin cocoanut oil, the choicest oil comes from Cochin . This product, being more carefully cultivated and refined than the other grades, is whiter, cleaner and contains a smaller percentage of free acid. Ceylon cocoanut oil, coming chiefly from Ceylon, is usually of a yellowish tint and more acrid in odor than Cochin oil. Continental cocoanut oil is obtained from the dried kernels, the copra, which are shipped to Europe in large quantities, where the oil is extracted. These dried kernels yield 60 to 70 per cent oil. This product is generally superior to the Ceylon oil and may be used as a very satisfactory substitute for Cochin oil, in soap manufacture, provided it is low in free acid and of good color. The writer has employed it satisfactorily in the whitest and finest of toilet soaps without being able to distinguish any disadvantage to the Cochin oil. Since continental oil is usually cheaper than Cochin oil, it is advisable to use it, as occasion permits.

Cocoanut oil is used extensively in toilet soap making, usually in connection with tallow. When used alone the soap made from this oil forms a lather, which comes up rapidly but which is fluffy and dries quickly. A pure tallow soap lathers very much slower but produces a more lasting lather. Thus the advantage of using cocoanut oil in soap is seen. It is further used in making a cocoanut oil soap by the cold process also for "fake" or filled soaps. The fatty acid content readily starts the saponification which takes place easily with a strong lye . Where large quantities of the oil are saponified care must be exercised as the soap formed suddenly rises or puffs up and may boil over. Cocoanut oil soap takes up large quantities of water, cases having been cited where a 500 per cent. yield has been obtained. This water of course dries out again upon exposure to the air. The soap is harsh to the skin, develops rancidity and darkens readily.

There are several grades of palm oil in commerce, but in toilet soap making it is advisable to utilize only Lagos palm oil, which is the best grade. Where it is desired to maintain the color of the soap this oil produces, a small quantity of the lower or "brass" grade of palm oil may be used, as the soap made from the better grades of oil gradually bleaches and loses its orange yellow color.

Palm oil produces a crumbly soap which cannot readily be milled and is termed "short." When used with tallow and cocoanut oil, or 20 to 25 per cent. cocoanut oil, it produces a very satisfactory toilet soap. In the saponification of palm oil it is not advisable to combine it with tallow in the kettle, as the two do not readily mix.

Since the finished soap has conveyed to it the orange color of the oil, the oil is bleached before saponification. Oxidation readily destroys the coloring matter, while heat and light assist materially. The methods generally employed are by the use of oxygen developed by bichromates and hydrochloric acid and the direct bleaching through the agency of the oxygen of the air.

CHROME BLEACHING OF PALM OIL.

The chrome process of bleaching palm oil is more rapid and the oxygen thus derived being more active will bleach oils which air alone cannot. It depends upon the reaction:

in which the oxygen is the active principle. In practice it is found necessary to use an excess of acid over that theoretically indicated.

For the best results an oil should be chosen containing under 2 per cent. impurities and a low percentage of free fatty acids. Lagos oil is best adapted to these requirements. The oil is melted by open steam from a jet introduced through the bung, the melted oil and condensed water running to the store tank through two sieves to remove the fibrous material and gross impurities. The oil thus obtained contains fine earthy and fibrous material and vegetable albuminous matter which should be removed, as far as possible, since chemicals are wasted in their oxidation and they retard the bleaching. This is best done by boiling the oil for one hour with wet steam and 10 per cent. solution of common salt in a lead-lined or wooden tank. After settling over night the brine and impurities are removed by running from a cock at the bottom of the vat and the oil is run out into the bleaching tank through an oil cock, situated about seven inches from the bottom.

The bleaching tank is a lead-lined iron tank of the approximate dimensions of 4 feet deep, 4 feet long and 3-1/2 feet wide, holding about 1-1/2 tons. The charge is one ton. A leaden outlet pipe is fixed at the bottom, to which is attached a rubber tube closed by a screw clip. A plug also is fitted into the lead outlet pipe from above. Seven inches above the lower outlet is affixed another tap through which the oil is drawn off.

The tank is further equipped with a wet steam coil and a coil arranged to allow thorough air agitation, both coils being of lead. A good arrangement is to use one coil to deliver either air or steam. These coils should extend as nearly as possible over the entire bottom of the tank and have a number of small downward perforations, so as to spread the agitation throughout the mass.

The temperature of the oil is reduced by passing in air to 110? F. and 40 pounds of fine common salt per ton added through a sieve. About one-half of the acid is now poured in and this is followed by the sodium bichromate in concentrated solution, previously prepared in a small lead vat or earthen vessel by dissolving 17 pounds of bichromate in 45 pounds commercial hydrochloric acid. This solution should be added slowly and should occupy three hours, the whole mass being thoroughly agitated with air during the addition and for one hour after the last of the bleaching mixture has been introduced. The whole mixture is now allowed to settle for one hour and the exhausted chrome liquors are then run off from the lower pipe to a waste tank. About 40 gallons of water are now run into the bleached oil and the temperature raised by open steam to 150? to 160? F. The mass is then allowed to settle over night.

One such wash is sufficient to remove the spent chrome liquor completely, provided ample time is allowed for settling. A number of washings given successively with short periods of settling do not remove the chrome liquors effectually. The success of the operation depends entirely upon the completeness of settling.

The wash water is drawn off as before and the clear oil run to storage tanks or to the soap kettle through the upper oil cock.

The waste liquors are boiled with wet steam and the oil skimmed from the surface, after which the liquors are run out through an oil trap.

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