The Project Gutenberg eBook ofSoap-Making ManualThis ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online atwww.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.Title: Soap-Making ManualAuthor: Edgar George ThomssenRelease date: October 22, 2010 [eBook #34114]Most recently updated: January 7, 2021Language: EnglishCredits: Produced by David Clarke, Josephine Paolucci and the OnlineDistributed Proofreading Team at https://www.pgdp.net. (Thisfile was produced from images generously made availableby The Internet Archive/American Libraries.)*** START OF THE PROJECT GUTENBERG EBOOK SOAP-MAKING MANUAL ***
This ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online atwww.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.
Title: Soap-Making ManualAuthor: Edgar George ThomssenRelease date: October 22, 2010 [eBook #34114]Most recently updated: January 7, 2021Language: EnglishCredits: Produced by David Clarke, Josephine Paolucci and the OnlineDistributed Proofreading Team at https://www.pgdp.net. (Thisfile was produced from images generously made availableby The Internet Archive/American Libraries.)
Title: Soap-Making Manual
Author: Edgar George Thomssen
Author: Edgar George Thomssen
Release date: October 22, 2010 [eBook #34114]Most recently updated: January 7, 2021
Language: English
Credits: Produced by David Clarke, Josephine Paolucci and the OnlineDistributed Proofreading Team at https://www.pgdp.net. (Thisfile was produced from images generously made availableby The Internet Archive/American Libraries.)
*** START OF THE PROJECT GUTENBERG EBOOK SOAP-MAKING MANUAL ***
NEW YORKD. VAN NOSTRAND COMPANYEight Warren Street1922Copyright1922ByD. VAN NOSTRAND COMPANYPrinted in the United States of America
The material contained in this work appeared several years ago in serial form in the American Perfumer and Essential Oil Review. Owing to the numerous requests received, it has been decided to now place before those interested, these articles in book form. While it is true that the works pertaining to the soapmaking industry are reasonably plentiful, books are quite rare, however, which, in a brief volume, will clearly outline the processes employed together with the necessary methods of analyses from a purely practical standpoint. In the work presented the author has attempted to briefly, clearly, and fully explain the manufacture of soap in such language that it might be understood by all those interested in this industry. In many cases the smaller plants find it necessary to dispense with the services of a chemist, so that it is necessary for the soapmaker to make his own tests. The tests outlined, therefore, are given as simple as possible to meet this condition. The formulae submitted are authentic, and in many cases are now being used in soapmaking.
In taking up the industry for survey it has been thought desirable to first mention and describe the raw materials used; second, to outline the processes of manufacture; third, to classify the methods and illustrate by formulae the composition of various soaps together with their mode of manufacture; fourth, to enumerate the various methods of glycerine recovery, including the processes of saponification, and, fifth, to give the most important analytical methods which are of value to controlthe process of manufacture and to determine the purity and fitness of the raw material entering into it.
It is not the intention of the author to go into great detail in this work, nor to outline to any great extent the theoretical side of the subject, but rather to make the work as brief as possible, keeping the practical side of the subject before him and not going into concise descriptions of machinery as is very usual in works on this subject. Illustrations are merely added to show typical kinds of machinery used.
The author wishes to take this opportunity of thanking Messrs. L. S. Levy and E. W. Drew for the reading of proof, and Mr. C. W. Aiken of the Houchin-Aiken Co., for his aid in making the illustrations a success, as well as others who have contributed in the compiling of the formulae for various soaps. He trusts that this work may prove of value to those engaged in soap manufacture.
E. G. T.
January, 1922
Transcriber's note: This is a series of articles collected into a book. There are differences in spelling and punctuation in the different chapters (e.g. cocoanut in one chapter and coconut in another). These differences were left in the text as they appeared.
CHAPTER I.Page.Raw Materials Used in Soap Making1-301. Soap Defined12. Oils and Fats1-23. Saponification Defined2-34. Fats and Oils Used in Soap Manufacture3-4Fullers' Earth Process for Bleaching Tallow4-6Method for Further Improvement of Color in Tallow6Vegetable Oils6-9Chrome Bleaching of Palm Oil9-12Air Bleaching of Palm Oil12-165. Rancidity of Oils and Fats16-18Prevention of Rancidity186. Chemical Constants of Oils and Fats18-197. Oil Hardening or Hydrogenating19-218. Grease21-229. Rosin (Colophony, Yellow Rosin, Resina)22-2310. Rosin Saponification23-2411. Naphthenic Acids24-2512. Alkalis25-26Caustic Soda26Caustic Potash26-28Sodium Carbonate (Soda Ash)28-29Potassium Carbonate2913. Additional Material Used in Soap Making29-30CHAPTER II.Construction and Equipment of a Soap Plant31-34CHAPTER III.Classification of Soap Making Methods35-461. Full Boiled Soaps36-422. Cold Process43-443. Carbonate Saponification45-46CHAPTER IV.Classification of Soaps47-1041. Laundry Soap48Semi-Boiled Laundry Soap49-50Settled Rosin Soap50-542. Chip Soap54-55Cold Made Chip Soap55-56Unfilled Chip Soap563. Soap Powders56-59Light Powders60-614. Scouring Powders615. Scouring Soap61-626. Floating Soap62-657. Toilet Soap65-68Cheaper Toilet Soaps68-69Run and Glued-up Soaps69-71Curd Soap71-72Cold Made Toilet Soaps72-73Perfuming and Coloring Toilet Soaps73-75Coloring Soap75-768. Medicinal Soaps76-77Sulphur Soaps77Tar Soap77Soaps Containing Phenols77-78Peroxide Soap78Mercury Soaps78Less Important Medicinal Soaps78-799. Castile Soap79-8110. Eschweger Soap81-8211. Transparent Soap82-84Cold Made Transparent Soap84-8712. Shaving Soaps87-90Shaving Powder90Shaving Cream90-9313. Pumice or Sand Soaps93-9414. Liquid Soaps94-9515. Use of Hardened Oils in Toilet Soaps96-9816. Textile Soaps98Scouring and Fulling Soaps for Wool98-100Wool Thrower's Soap100-101Worsted Finishing Soaps101Soaps Used in the Silk Industry101-103Soaps Used for Cotton Goods103-10417. Sulphonated Oils104-105CHAPTER V.Glycerine Recovery105-1261. Methods of Saponification105-106Recovery of Glycerine from Spent Lye106-113Twitchell Process113-118Autoclave Saponification118Lime Saponification118-120Acid Saponification120-121Aqueous Saponification121Splitting Fats with Ferments121-123Krebitz Process123-1252. Distillation of Fatty Acids125-126CHAPTER VI.Analytical Methods127-1641. Analysis of Oils and Fats128Free Fatty Acids128-130Moisture130Titer130-132Determination of Unsaponifiable Matter132-133Test for Color of Soap133-134Testing of Alkalis Used in Soap Making134-1372. Soap Analysis137-138Moisture138-139Free Alkali or Acid139-142Insoluble Matter143Starch and Gelatine143-144Total Fatty and Resin Acids144Determination of Rosin144-147Total Alkali147-148Unsaponifiable Matter148Silica and Silicates148-149Glycerine in Soap149-150Sugar in Soap1503. Glycerine Analysis150-151Sampling151Analysis151-154Acetin Process for the Determination of Glycerol155-156The Method156-159Ways of Calculating Actual Glycerol Contents159-160Bichromate Process for Glycerol DeterminationReagents Required160-161The Method161-162Sampling Crude Glycerine162-164CHAPTER VIIStandard Methods for the Sampling and Analysis of Commercial Fats and Oils165-1951. Scope, Applicability and Limitations of the Methods165-166Scope165Applicability166Limitations166Sampling166-169Tank Cars166-167Barrels, Tierces, Casks, Drums, and Other Packages1682. Analysis169-183Sample169Moisture and Volatile Matter170-172Insoluble Impurities172-173Soluble Mineral Matter173Free Fatty Acids174Titer174-175Unsaponifiable Matter176-177Iodine Number-Wijs Method177-181Saponification Number (Koettstorfer Number)181Melting Point181-182Cloud Test182-1843. Notes of the Above Methods184-196Sampling183Moisture and Volatile Matter184-187Insoluble Impurities187Soluble Mineral Matter187-188Free Fatty Acid188-189Titer189Unsaponified Matter190-193Melting Point193-196Plant and Machinery198-219Illustrations of Machinery and Layouts of the Plant of a Modern Soap Making Establishment198-219Appendix219-237Useful TablesIndex239
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 (caustic soda lye), or potassium hydroxide (caustic potash). 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.
There is no sharp distinction between fat and oil. By "oil" the layman has the impression of a liquid which atwarm temperature will flow as a slippery, lubricating, viscous fluid; by "fat" he understands a greasy, solid substance unctuous to the touch. It thus becomes necessary to differentiate the oils and fats used in the manufacture of soap.
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.
Glycerine, being a trihydric alcohol, has three atoms of hydrogen which are replaceable by three univalent radicals of the higher members of the fatty acids,e. g.,
OHORC3H5OH+ 3 ROH = C3H5OR+ 3 H2OOHOR
Glycerine plus 3 Fatty Alcohols equals Fat or Oil plus 3 Water.
Thus three fatty acid radicals combine with one glycerine to form a true neutral oil or fat which are called triglycerides. The fatty acids which most commonly enter into combination of fats and oils are lauric, myristic, palmitic, stearic and oleic acids and form the neutral oils or triglycerides derived from these,e. g., stearin, palmatin, olein. Mono and diglycerides are also present in fats.
When a fat or oil enters into chemical combination with one of the caustic hydrates in the presence of water, theprocess is called "saponification" and the new compounds formed are soap and glycerine, thus:
OROHC3H5OR+ 3 NaOH = C3H5OH+ 3 NaOROROH
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.
There are also other means of saponification, as, the hydrolysis of an oil or fat by the action of hydrochloric or sulfuric acid, by autoclave and by ferments or enzymes. By these latter processes the fatty acids and glycerine are obtained directly, no soap being formed.
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 (oleic acid) 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 dependshould 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.
Tallowis the name given to the fat extracted from the solid fat or "suet" of cattle, sheep or horses. The quality varies greatly, depending upon the seasons of the year, the food and age of the animal and the method of rendering. It comes to the market under the distinction of edible and inedible, a further distinction being made in commerce as beef tallow, mutton tallow or horse tallow. The better quality is white and bleaches whiter upon exposure to air and light, though it usually has a yellowish tint, a well defined grain and a clean odor. It consists chiefly of stearin, palmitin and olein. Tallow is by far the most extensively used and important fat in the making of soap.
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.
From one to two tons of tallow are melted out into the bleaching tank. This tank is jacketed, made of iron and provided with a good agitator designed to stir up sediment or a coil provided with tangential downward opening perforations and a draw-off cock at the bottom. The coil is the far simpler arrangement, more cleanly and less likely to cause trouble. By this arrangement compressed air which is really essential in the utilization of the press (see later) is utilized for agitation. A dry steam coil in an ordinary tank may be employed in place of a jacketed tank, which lessens the cost of installation.
The tallow in the bleaching tank is heated to 180° F. (82° C.) 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. (71° C).
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.
One of the difficulties experienced in the process is the heating of the press to a temperature sufficient to prevent solidification of the fat without raising the press to too great a temperature. To overcome this the first plate is heated by wet steam. Air delivered from a blower and heated by passage through a series of coils raised to a high temperature by external application of heat (super-heated steam) is then substituted for the steam. The moisture produced by the condensation of the steam is vaporized by the hot air and carried on gradually to each succeeding plate where it again condenses and vaporizes. In this way the small quantity of water is carried through the entire press, raising its temperature to 80°-100° C. This temperature is subsequently maintained by the passage of hot air. By this method of heating the poor conductivity of hot air is overcome through the intermediary action of a liquid vapor and the latent heat of steam is utilized to obtain the initial rise in temperature. To heat a small press economically where conditions are such that a large output is not required the entire pressmay be encased in a small wooden house which can be heated by steam coils. The cake in the press is heated for some time after the filtration is complete to assist drainage. After such treatment the cake should contain approximately 15 per cent. fat and 25 per cent. water. The cake is now removed from the press and transferred to a small tank where it is treated with sufficient caustic soda to convert the fat content into soap.
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.
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.
Cocoanut Oil, as the name implies, is obtained from the fruit of the cocoanut palm. This oil is a solid, white fat at ordinary temperature, having a bland taste and a characteristicodor. It is rarely adulterated and is very readily saponified. In recent years the price of this oil has increased materially because cocoanut oil is now being used extensively for edible purposes, especially in the making of oleomargarine. Present indications are that shortly very little high grade oil will be employed for soap manufacture since the demand for oleomargarine is constantly increasing and since new methods of refining the oil for this purpose are constantly being devised.
The oil is found in the market under three different grades: (1) Cochin cocoanut oil, the choicest oil comes from Cochin (Malabar). This product, being more carefully cultivated and refined than the other grades, is whiter, cleaner and contains a smaller percentage of free acid. (2) Ceylon cocoanut oil, coming chiefly from Ceylon, is usually of a yellowish tint and more acrid in odor than Cochin oil. (3) Continental cocoanut oil (Copra, Freudenberg) 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 oilin 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 (25°-35° B.). 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.
Palm Kernel Oil, which is obtained from the kernels of the palm tree of West Africa, is used in soap making to replace cocoanut oil where the lower price warrants its use. It resembles cocoanut oil in respect to saponification and in forming a very similar soap. Kernel oil is white in color, has a pleasant nutty odor when fresh, but rapidly develops free acid, which runs to a high percentage.
Palm Oilis produced from the fruit of the several species of the palm tree on the western coast of Africa generally, but also in the Philippines. The fresh oil has a deep orange yellow tint not destroyed by saponification, a sweetish taste and an odor of orris root or violet which is also imparted to soap made from it. The methods by which the natives obtain the oil are crude and depend upon a fermentation, or putrefaction. Large quantities are said to be wasted because of this fact. The oil contains impurities in the form of fermentable fibre and albuminous matter, and consequently develops free fatty acid rapidly. Samples tested for free acid have been found to have hydrolized completely and one seldom obtains an oil with low acid content. Because of this high percentage of free fatty acid, the glycerine yield is small, though the neutral oil should produce approximately 12 per cent. glycerine. Somewriters claim that glycerine exists in the free state in palm oil. The writer has washed large quantities of the oil and analyzed the wash water for glycerine. The results showed that the amount present did not merit its recovery. Most soap makers do not attempt to recover the glycerine from this oil, when used alone for soap manufacture.
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.
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:
Na2Cr2O7+ 8HCl = Cr2Cl6+ 2NaCl + 7O.
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 (about 1/8 inch mesh) 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 (2 per cent. dry salt on weight of oil used) 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 airto 110° F. and 40 pounds of fine common salt per ton added through a sieve. About one-half of the acid (40 pounds of concentrated commercial hydrochloric 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.
By following the above instructions carefully it is possible to bleach one ton of palm oil with 17 pounds of bichromate of soda and 85 pounds hydrochloric acid.
The spent liquors should be a bright green color. Should they be of a yellow or brownish shade insufficient acid hasbeen allowed and more must be added to render the whole of the oxygen available.
If low grade oils are being treated more chrome will be necessary, the amount being best judged by conducting the operation as usual and after the addition of the bichromate, removing a sample of the oil, washing the sample and noting the color of a rapidly cooled sample.
A little practice will enable the operator to judge the correspondence between the color to be removed and the amount of bleaching mixture to be added.
To obtain success with this process the method of working given must be adhered to even in thesmallest detail. This applies to the temperature at which each operation is carried out particularly.
The method of conducting this process is identical with the chrome process to the point where the hydrochloric acid is to be added to the oil. In this method no acid or chrome is necessary, as the active bleaching agent is the oxygen of the air.
The equipment is similar to that of the former process, except that a wooden tank in which no iron is exposed will suffice to bleach the oil in. The process depends in rapidity upon the amount of air blown through the oil and its even distribution. Iron should not be present or exposed to the oil during bleaching, as it retards the process considerably.
After the impurities have been removed, as outlined under the chrome process, the temperature of the oil is raised by open steam to boiling. The steam is then shut off and air allowed to blow through the oil until it is completely bleached, the temperature being maintained above 150° F. by occasionally passing in steam. Usually a ton of oil is readily and completely bleached after the air hasbeen passed through it for 18 to 20 hours, provided the oil is thoroughly agitated by a sufficient flow of air.
If the oil has been allowed to settle over night, it is advisable to run off the condensed water and impurities by the lower cock before agitating again the second day.
When the oil has been bleached to the desired color, which can be determined by removing a sample and cooling, the mass is allowed to settle, the water run off to a waste tank from which any oil carried along may be skimmed off and the supernatant clear oil run to the storage or soap kettle.
In bleaching by this process, while the process consumes more time and is not as efficient in bleaching the lower grade oils, the cost of bleaching is less and with a good oil success is more probable, as there is no possibility of any of the chrome liquors being present in the oil. These give the bleached oil a green tint when the chrome method is improperly conducted and they are not removed.
Instead of blowing the air through it, the heater oil may be brought into contact with the air, either by a paddle wheel arrangement, which, in constantly turning, brings the oil into contact with the air, or by pumping the heated oil into an elevated vessel, pierced with numerous fine holes from which the oil continuously flows back into the vessel from which the oil is pumped. While in these methods air, light and heat act simultaneously in the bleaching of the oil, the equipment required is too cumbersome to be practical.
Recent investigations[1]in bleaching palm oil by oxygen have shown that not only the coloring matter but the oil itself was affected. In bleaching palm oil for 30 hours with air the free fatty acid content rose and titer decreased considerably.
Olive Oil, which comes from the fruit of the olive trees, varies greatly in quality, according to the method by which it is obtained and according to the tree bearing the fruit. Three hundred varieties are known in Italy alone. Since the larger portion of olive oil is used for edible purposes, a lower grade, denatured oil, denatured because of the tariff, is used for soap manufacture in this country. The oil varies in color from pale green to golden yellow. The percentage of free acid in this oil varies greatly, though the oil does not turn rancid easily. It is used mainly in the manufacture of white castile soap.
Olive oil foots, which is the oil extracted by solvents after the better oil is expressed, finds its use in soap making mostly in textile soaps for washing and dyeing silks and in the production of green castile soaps.
Other oils, as poppy seed oil, sesame oil, cottonseed oil, rape oil, peanut (arachis) oil, are used as adulterants for olive oil, also as substitutes in the manufacture of castile soap, since they are cheaper than olive oil.
Cottonseed Oilis largely used in the manufacture of floating and laundry soaps. It may be used for toilet soaps where a white color is not desired, as yellow spots appear on a finished soap in which it has been used after having been in stock a short time.
Corn Oil and Soya Bean Oilare also used to a slight extent in the manufacture of toilet soaps, although the oils form a soap of very little body. Their soaps also spot yellow on aging.
Corn oil finds its greatest use in the manufacture of soap for washing automobiles. It is further employed for the manufacture of cheap liquid soaps.
Fatty Acidsare also used extensively in soap manufacture. While the soap manufacturer prefers to use a neutral oil or fat, since from these the by-product glycerine isobtained, circumstances arise where it is an advantage to use the free fatty acids. Red oil (oleic acid, elaine) and stearic acid are the two fatty acids most generally bought for soap making. In plants using the Twitchell process, which consists in splitting the neutral fats and oils into fatty acids and glycerine by dilute sulphuric acid and producing their final separation by the use of so-called aromatic sulphonic acids, these fatty acids consisting of a mixture of oleic, stearic, palmitic acids, etc., are used directly after having been purified by distillation, the glycerine being obtained from evaporating the wash water.
Oleic acid (red oil) and stearic acid are obtained usually by the saponification of oils, fats and greases by acid, lime or water under pressure or Twitchelling. The fatty acids thus are freed from their combination with glycerine and solidify upon cooling, after which they are separated from the water and pressed at a higher or lower temperature. The oleic acid, being liquid at ordinary temperature, together with some stearic and palmitic acid, is thus pressed out. These latter acids are usually separated by distillation, combined with the press cake further purified and sold as stearic acid.
The red oil, sometimes called saponified red oil, is often semi-solid, resembling a soft tallow, due to the presence of stearic acid. The distilled oils are usually clear, varying in color from light to a deep brown. Stearic acid, which reaches the trade in slab form, varies in quality from a soft brown, greasy, crumbly solid of unpleasant odor to a snow white, wax-like, hard, odorless mass. The quality of stearic acid is best judged by the melting point, since the presence of any oleic acid lowers this. The melting point of the varieties used in soap manufacture usually ranges from 128° to 132° F. Red oil is used in the manufacture of textile soaps, replacing olive oil foots soap forthis purpose, chlorophyll being used to color the soap green. Stearic acid, being the hard firm fatty acid, may be used in small quantities to give a better grade of soap body and finish. In adding this substance it should always be done in the crutcher, as it will not mix in the kettle. It finds its largest use for soap, however, in the manufacture of shaving soaps and shaving creams, since it produces the non-drying creamy lather so greatly desired for this purpose. Both red oil and stearic acid being fatty acids, readily unite with the alkali carbonates, carbon dioxide being formed in the reaction and this method is extensively used in the formation of soap from them.
Rancidity in neutral oils and fats is one of the problems the soap manufacturer has to contend with. The mere saying that an oil is rancid is no indication of its being high in free acid. The two terms rancidity and acidity are usually allied. Formerly, the acidity of a fat was looked upon as the direct measure of its rancidity. This idea is still prevalent in practice and cannot be too often stated as incorrect. Fats and oils may beacid, orrancid, oracid and rancid. In an acid fat there has been a hydrolysis of the fat and it has developed a rather high percentage of free acid. A rancid fat is one in which have been developed compounds of an odoriferous nature. An acid and rancid fat is one in which both free acid and organic compounds of the well known disagreeable odors have been produced.
It cannot be definitely stated just how this rancidity takes place, any more than just what are the chemical products causing rancidity. The only conclusion that one may draw is that the fats are first hydrolyzed or split up into glycerine and free fatty acids. This is followed by an oxidation of the products thus formed.
Moisture, air, light, enzymes (organized ferments) and bacteria are all given as causes of rancidity.
It seems very probable that the initial splitting of the fats is caused by enzymes, which are present in the seeds and fruits of the vegetable oils and tissue of animal fats, in the presence of moisture. Lewkowitsch strongly emphasizes this point and he is substantiated in his idea by other authorities. Others hold that bacteria or micro-organisms are the cause of this hydrolysis, citing the fact that they have isolated various micro-organisms from various fats and oils. The acceptance of the bacterial action would explain the various methods of preservation of oils and fats by the use of antiseptic preparations. It cannot, however, be accepted as a certainty that bacteria cause the rancidity of fats.
The action of enzymes is a more probable explanation.
The hydrolysis of fats and oils is accelerated when they are allowed to remain for some time in the presence of organic non-fats. Thus, palm oil, lower grades of olive oil, and tallow, which has been in contact with the animal tissue for a long time, all contain other nitrogenous matter and exhibit a larger percentage of free fatty acid than the oils and fats not containing such impurities.
Granting this initial splitting of the fat into free fatty acids and glycerine, this is not a sufficient explanation. The products thus formed must be acted upon by air and light. It is by the action of these agents that there is a further action upon the products, and from this oxidation we ascertain by taste and smell (chemical means are still unable to define rancidity) whether or not a fat is rancid. While some authorities have presumed to isolate some of these products causing rancidity, we can only assume the presence of the various possible compounds produced by the actionof air and light which include oxy fatty acids, lactones, alcohols, esters, aldehydes and other products.
The soap manufacturer is interested in rancidity to the extent of the effect upon the finished soap. Rancid fats form darker soaps than fats in the neutral state, and very often carry with them the disagreeable odor of a rancid oil. Further, a rancid fat or oil is usually high in free acid. It is by no means true, however, that rancidity is a measure for acidity, for as has already been pointed out, an oil may be rancid and not high in free acid.
The percentage of free fatty acid is of even greater importance in the soap industry. The amount of glycerine yield is dependent upon the percentage of free fatty acid and is one of the criterions of a good fat or oil for soap stock.