Since moisture, air, light and enzymes, produced by the presence of organic impurities, are necessary for the rancidity of a fat or oil, the methods of preventing rancidity are given. Complete dryness, complete purification of fats and oils and storage without access of air or light are desirable. Simple as these means may seem, they can only be approximated in practice. The most difficult problem is the removal of the last trace of moisture. Impurities may be lessened very often by the use of greater care. In storing it is well to store in closed barrels or closed iron tanks away from light, as it has been observed that oils and fats in closed receptacles become rancid less rapidly than those in open ones, even though this method of storing is only partially attained. Preservatives are also used, but only in edible products, where their effectiveness is an open question.
Besides the various physical properties of oils and fats,such as color, specific gravity, melting point, solubility, etc., they may be distinguished chemically by a number of chemical constants. These are the iodine number, the acetyl value, saponification number, Reichert-Meissl number for volatile acids, Hehner number for insoluble acids. These constants, while they vary somewhat with any particular oil or fat, are more applicable to the edible products and are criterions where any adulteration of fat or oil is suspected. The methods of carrying out the analyses of oils and fats to obtain these constants are given in the various texts[2]on oils and fats, and inasmuch as they are not of great importance to the soap industry they are merely mentioned here.
It is very well known that oils and fats vary in consistency and hardness, depending upon the glycerides forming same. Olein, a combination of oleic acid and glycerine, as well as oleic acid itself largely forms the liquid portion of oils and fats. Oleic acid (C18H34O2) is an unsaturated acid and differs from stearic acid (C18H36O2), the acid forming the hard firm portion of oils and fats, by containing two atoms of hydrogen less in the molecule. Theoretically it should be a simple matter to introduce two atoms of hydrogen into oleic acid or olein, and by this mere addition convert liquid oleic acid and olein into solid stearic acid and stearine.
For years this was attempted and all attempts to apply the well known methods of reduction (addition of hydrogen) in organic chemistry, such as treatment with tin and acid, sodium amalgam, etc., were unsuccessful. In recent years, however, it has been discovered that in the presence of a catalyzer, nickel in finely divided formor the oxides of nickel are usually employed, the process of hydrogenating an oil is readily attained upon a practical basis.
The introduction of hardened oils has opened a new source of raw material for the soap manufacturer in that it is now possible to use oils in soap making which were formerly discarded because of their undesirable odors. Thus fish or train oils which had up to the time of oil hydrogenating resisted all attempts of being permanently deodorized, can now be employed very satisfactorily for soap manufacture. A Japanese chemist, Tsujimoto[3]has shown that fish oils contain an unsaturated acid of the composition C18H28O2, for which he proposed the name clupanodonic acid. By the catalytic hardening of train oils this acid passes to stearic acid and the problem of deodorizing these oils is solved.[4]
At first the introduction of hardened oils for soap manufacture met with numerous objections, due to the continual failures of obtaining a satisfactory product by the use of same. Various attempts have now shown that these oils, particularly hardened train oils, produce extraordinarily useful materials for soap making. These replace expensive tallow and other high melting oils. It is of course impossible to employ hardened oils alone, as a soap so hard would thus be obtained that it would be difficultly soluble in water and possess very little lathering quality. By the addition of 20-25% of tallow oil or some other oil forming a soft soap a very suitable soap for household use may be obtained. Ribot[5]discusses this matter fully. Hardened oils readily saponify, may beperfumed without any objections and do not impart any fishy odor to an article washed with same. Meyerheim[6]states that through the use of hydrogenated oils the hardness of soap is extraordinarily raised, so that soap made from hardened cottonseed oil is twelve times as hard as the soap made from ordinary cottonseed oil. This soap is also said to no longer spot yellow upon aging, and as a consequence of its hardness, is able to contain a considerably higher content of rosin through which lathering power and odor may be improved. Hardened oils can easily be used for toilet soap bases, provided they are not added in too great a percentage.
The use of hardened oils is not yet general, but there is little doubt that the introduction of this process goes a long way toward solving the problem of cheaper soap material for the soap making industry.
Grease varies so greatly in composition and consistency that it can hardly be classed as a distinctive oil or fat. It is obtained from refuse, bones, hides, etc., and while it contains the same constituents as tallow, the olein content is considerably greater, which causes it to be more liquid in composition. Grease differs in color from an off-white to a dark brown. The better qualities are employed in the manufacture of laundry and chip soap, while the poorer qualities are only fit for the cheapest of soaps used in scrubbing floors and such purposes. There is usually found in grease a considerable amount of gluey matter, lime and water. The percentage of free fatty acid is generally high.
The darker grades of grease are bleached before being used. This is done by adding a small quantity of sodium nitrate to the melted grease and agitating, thenremoving the excess saltpeter by decomposing with sulphuric acid. A better method of refining, however, is by distillation. The chrome bleach is also applicable.
Rosin is the residue which remains after the distillation of turpentine from the various species of pines. The chief source of supply is in the States of Georgia North and South Carolina. It is a transparent, amber colored hard pulverizable resin. The better grades are light in color and known as water white (w. w.) and window glass (w. g.). These are obtained from a tree which has been tapped for the first year. As the same trees are tapped from year to year, the product becomes deeper and darker in color until it becomes almost black.
The constituents of rosin are chiefly (80-90%) abietic acid or its anhydride together with pinic and sylvic acids. Its specific gravity is 1.07-1.08, melting point about 152.5 C., and it is soluble in alcohol, ether, benzine, carbon disulfide, oils, alkalis and acetic acid. The main use of rosin, outside of the production of varnishes, is in the production of laundry soaps, although a slight percentage acts as a binder and fixative for perfumes in toilet soaps and adds to their detergent properties. Since it is mainly composed of acids, it readily unites with alkaline carbonates, though the saponification is not quite complete and the last portion must be completed through the use of caustic hydrates, unless an excess of 10% carbonate over the theoretical amount is used. A lye of 20° B. is best adapted to the saponification of rosin when caustic hydrates are employed for this purpose, since weak lyes cause frothing. While it is sometimes considered that rosin is an adulterant for soap, this is hardly justifiable, as it adds to the cleansing properties of soap. Soaps containingrosin are of the well known yellowish color common to ordinary laundry soaps. The price of rosin has so risen in the last few years that it presents a problem of cost to the soap manufacturer considering the price at which laundry soaps are sold.
As has been stated, rosin may be saponified by the use of alkaline carbonates. On account of the possibility of the soap frothing over, the kettle in which the operation takes place should be set flush with the floor, which ought to be constructed of cement. The kettle itself is an open one with round bottom, equipped with an open steam coil and skimmer pipe, and the open portion is protected by a semi-circular rail. A powerful grid, having a 3-inch mesh, covers one-half of the kettle, the sharp edges protruding upwards.
The staves from the rosin casks are removed at the edge of the kettle, the rosin placed on the grid and beaten through with a hammer to break it up into small pieces.
To saponify a ton of rosin there are required 200 lbs. soda ash, 1,600 lbs. water and 100 lbs. salt. Half the water is run into the kettle, boiled, and then the soda ash and half the salt added. The rosin is now added through the grid and the mixture thoroughly boiled. As carbon dioxide is evolved by the reaction the boiling is continued for one hour to remove any excess of this gas. A portion of the salt is gradually added to grain the soap well and to keep the mass in such condition as to favor the evolution of gas. The remainder of the water is added to close the soap and boiling continued for one or two hours longer. At this point the kettle must be carefully watched or it will boil over through the furtherescape of carbon dioxide being hindered. The mass, being in a frothy condition, will rapidly settle by controlling the flow of steam. The remaining salt is then scattered in and the soap allowed to settle for two hours or longer. The lyes are then drained off the top. If the rosin soap is required for toilet soaps, it is grained a second time. The soap is now boiled with the water caused by the condensation of the steam, which changes it to a half grained soap suitable for pumping. A soap thus made contains free soda ash 0.15% or less, free rosin about 15%. The mass is then pumped to the kettle containing the soap to which it is to be added at the proper stage. The time consumed in thus saponifying rosin is about five hours.
The naphtha or crude petroleum of the various provinces in Europe, as Russia, Galacia, Alsace and Roumania yield a series of bodies of acid character upon refining which are designated under the general name of naphthenic acids. These acids are retained in solution in the alkaline lyes during the distillation of the naphtha in the form of alkaline naphthenates. Upon adding dilute sulphuric acid to these lyes the naphthenates are decomposed and the naphthenic acids float to the surface in an oily layer of characteristic disagreeable odor and varying from yellow to brown in color[7]. In Russia particularly large quantities of these acids are employed in the manufacture of soap.
The soaps formed from naphthenic acids have recently been investigated[8]and found to resemble the soaps made from cocoanut oil and palm kernel oil, in that they aredifficult to salt out and dissociate very slightly with water. The latter property makes them valuable in textile industries when a mild soap is required as a detergent, e. g., in the silk industry. These soaps also possess a high solvent power for mineral oils and emulsify very readily. The mean molecular weight of naphthenic acids themselves is very near that of the fatty acids contained in cocoanut oil, and like those of cocoanut oil a portion of the separated acids are volatile with steam. The iodine number indicates a small content of unsaturated acids.
That naphthenic acids are a valuable soap material is now recognized, but except in Russia the soap is not manufactured to any extent at the present time.
The common alkali metals which enter into the formation of soap are sodium and potassium. The hydroxides of these metals are usually used, except in the so called carbonate saponification of free fatty acids in which case sodium and potassium carbonate are used. A water solution of the caustic alkalis is known as lye, and it is as lyes of various strengths that they are added to oils and fats to form soap. The density or weight of a lye is considerably greater than that of water, depending upon the amount of alkali dissolved, and its weight is usually determined by a hydrometer. This instrument is graduated by a standardized scale, and while all hydrometers should read alike in a liquid of known specific gravity, this is generally not the case, so that it is advisable to check a new hydrometer for accurate work against one of known accuracy. In this country the Baumé scale has been adopted, while in England a different graduation known as the Twaddle scale is used. The strength of a lye or any solution is determined by the distance the instrumentsinks into the solution, and we speak of the strength of a solution as so many degrees Baumé or Twaddle which are read to the point where the meniscus of the lye comes on the graduated scale. Hydrometers are graduated differently for liquids of different weights. In the testing of lyes one which is graduated from 0° to 50° B. is usually employed.
Caustic sodais received by the consumer in iron drums weighing approximately 700 lbs. each. The various grades are designated as 60, 70, 74, 76 and 77%. These percentages refer to the percentage of sodium oxide (Na2O) in 100 parts of pure caustic soda formed by the combination of 77-1/2 parts of sodium oxide and 22-1/2 parts of water, 77-1/2% being chemically pure caustic soda. There are generally impurities present in commercial caustic soda. These consist of sodium carbonate, sodium chloride or common salt and sometimes lime. It is manufactured by treating sodium carbonate in an iron vessel with calcium hydroxide or slaked lime, or by electrolysis of common salt. The latter process has yet been unable to compete with the former in price. Formerly all the caustic soda used in soap making was imported, and it was only through the American manufacturer using a similar container to that used by foreign manufacturers that they were able to introduce their product. This prejudice has now been entirely overcome and most of the caustic soda used in this country is manufactured here.
The output of the salts containing potassium is controlled almost entirely by Germany. Formerly the chief source of supply of potassium compounds was from the burned ashes of plants, but about fifty years ago the inexhaustible salt mines of Stassfurt, Germany, were discovered.The salt there mined contains, besides the chlorides and sulphates of sodium, magnesium, calcium and other salts, considerable quantities of potassium chloride, and the Stassfurt mines at present are practically the entire source of all potassium compounds, in spite of the fact that other localities have been sought to produce these compounds on a commercial basis, especially by the United States government.
After separating the potassium chloride from the magnesium chloride and other substances found in Stassfurt salts the methods of manufacture of caustic potash are identical to those of caustic soda. In this case, however, domestic electrolytic caustic potash may be purchased cheaper than the imported product and it gives results equal to those obtained by the use of the imported article, opinions to the contrary among soap makers being many. Most of the caustic potash in the United States is manufactured at Niagara Falls by the Niagara Alkali Co., and the Hooker Electrochemical Co., chlorine being obtained as a by-product. The latter concern employs the Townsend Cell, for the manufacture of electrolytic potash, and are said to have a capacity for making 64 tons of alkali daily.
Since the molecular weight of caustic potash (56) is greater than that of caustic soda (40) more potash is required to saponify a pound of fat. The resulting potash soap is correspondingly heavier than a soda soap. When salt is added to a potassium soap double decomposition occurs, the potassium soap being transformed to a sodium soap and the potassium uniting with the chlorine to form potassium chloride. This was one of the earliest methods of making a hard soap, especially in Germany, where potash was derived from leeching ashes of burned wood and plants.
While carbonate of soda is widely distributed in nature the source of supply is entirely dependent upon the manufactured product. Its uses are many, but it is especially important to the soap industry in the so called carbonate saponification of free fatty acids, as a constituent of soap powders, in the neutralization of glycerine lyes and as a filler for laundry soaps.
The old French Le Blanc soda process, which consists in treating common salt with sulphuric acid and reducing the sodium sulphate (salt cake) thus formed with carbon in the form of charcoal or coke to sodium sulphide, which when treated with calcium carbonate yields a mixture of calcium sulphide and sodium carbonate (black ash) from which the carbonate is dissolved by water, has been replaced by the more recent Solvay ammonia soda process. Even though there is a considerable loss of salt and the by-product calcium chloride produced by this process is only partially used up as a drying agent, and for refrigerating purposes, the Le Blanc process cannot compete with the Solvay process, so that the time is not far distant when the former will be considered a chemical curiosity. In the Solvay method of manufacture sodium chloride (common salt) and ammonium bicarbonate are mixed in solution. Double decomposition occurs with the formation of ammonium chloride and sodium bicarbonate. The latter salt is comparatively difficultly soluble in water and crystallizes out, the ammonium chloride remaining in solution. When the sodium bicarbonate is heated it yields sodium carbonate, carbon dioxide and water; the carbon dioxide is passed into ammonia which is set free from the ammonium chloride obtained as above by treatment with lime (calcium oxide) calcium chloride being the by-product.
Sal soda or washing soda is obtained by recrystallizing a solution of soda ash in water. Large crystals of sal soda containing but 37% sodium carbonate are formed.
Potassium carbonate is not extensively used in the manufacture of soap. It may be used in the forming of soft soaps by uniting it with free fatty acids. The methods of manufacture are the same as for sodium carbonate, although a much larger quantity of potassium carbonate than carbonate of soda is obtained from burned plant ashes. Purified potassium carbonate is known aspearl ash.
Water is indispensable to the soap manufacturer. In the soap factoryhardwater is often the cause of much trouble. Water, which is the best solvent known, in passing through the crevices of rocks dissolves some of the constituents of these, and the water is known as hard. This hardness is of two kinds,temporaryandpermanent. Temporarily hard water is formed by water, which contains carbonic acid, dissolving a portion of calcium carbonate or carbonate of lime. Upon boiling, the carbonic acid is driven from the water and the carbonate, being insoluble in carbon dioxide free water, is deposited. This is the cause of boiler scale, and to check this a small amount of sal ammoniac may be added to the water, which converts the carbonate into soluble calcium chloride and volatile ammonium carbonate. Permanent hardness is caused by calcium sulphate which is soluble in 400 parts of water and cannot be removed by boiling.
The presence of these salts in water form insoluble lime soaps which act as inert bodies as far as their value for the common use of soap is concerned. Where the percentage of lime in water is large this should be removed.A method generally used is to add about 5% of 20° B. sodium silicate to the hard water. This precipitates the lime and the water is then sufficiently pure to use.
Salt, known as sodium chloride, is used to a large extent in soap making for "salting out" the soap during saponification, as well as graining soaps. Soap ordinarily soluble in water is insoluble in a salt solution, use of which is made by adding salt to the soap which goes into solution and throws any soap dissolved in the lyes out of solution. Salt may contain magnesium and calcium chlorides, which of course are undesirable in large amounts. The products on the market, however, are satisfactory, thus no detail is necessary.
Filling materialsused are sodium silicate, or water glass, talc, silex, pumice, starch, borax, tripoli, etc.
Besides these other materials are used in the refining of the oils and fats, and glycerine recovery, such as Fuller's earth, bichromates of soda or potash, sulphate of alumina, sulphuric and hydrochloric acids and alcohol.
A lengthy description of these substances is not given, as their modes of use are detailed elsewhere.
FOOTNOTES:[1]Seifensieder Zeit, 1913, 40, p. 687, 724, 740.[2]Official Methods, see Bull. 107, A. O. A. C., U. S. Dept. Agricult.[3]Journ. Coll. of Engin. Tokyo Imper. Univ. (1906), p. 1. Abs. Chem. Revue f. d. Fett-u. Harz, Ind. 16, p. 84; 20, p. 8.[4]Meyerheim—Fort. der Chem., Physik. und Physik. Chem. (1913), 8. 6, p. 293-307.[5]Seifs. Ztg. (1913), 40, p. 142.[6]Loc. cit.[7]Les Matieres Graisses (1914), 7, 69, p. 3367.[8]Zeit. f. Angew. Chem. (1914), 27, 1, p. 2-4.
[1]Seifensieder Zeit, 1913, 40, p. 687, 724, 740.
[1]Seifensieder Zeit, 1913, 40, p. 687, 724, 740.
[2]Official Methods, see Bull. 107, A. O. A. C., U. S. Dept. Agricult.
[2]Official Methods, see Bull. 107, A. O. A. C., U. S. Dept. Agricult.
[3]Journ. Coll. of Engin. Tokyo Imper. Univ. (1906), p. 1. Abs. Chem. Revue f. d. Fett-u. Harz, Ind. 16, p. 84; 20, p. 8.
[3]Journ. Coll. of Engin. Tokyo Imper. Univ. (1906), p. 1. Abs. Chem. Revue f. d. Fett-u. Harz, Ind. 16, p. 84; 20, p. 8.
[4]Meyerheim—Fort. der Chem., Physik. und Physik. Chem. (1913), 8. 6, p. 293-307.
[4]Meyerheim—Fort. der Chem., Physik. und Physik. Chem. (1913), 8. 6, p. 293-307.
[5]Seifs. Ztg. (1913), 40, p. 142.
[5]Seifs. Ztg. (1913), 40, p. 142.
[6]Loc. cit.
[6]Loc. cit.
[7]Les Matieres Graisses (1914), 7, 69, p. 3367.
[7]Les Matieres Graisses (1914), 7, 69, p. 3367.
[8]Zeit. f. Angew. Chem. (1914), 27, 1, p. 2-4.
[8]Zeit. f. Angew. Chem. (1914), 27, 1, p. 2-4.
No fixed plan for the construction and equipment of a soap plant can be given. The specifications for a soap factory to be erected or remodeled must suit the particular cases. Very often a building which was constructed for a purpose other than soap manufacture must be adapted for the production of soap. In either case it is a question of engineering and architecture, together with the knowledge obtained in practice and the final decision as to the arrangement is best solved by a conference with those skilled in each of these branches.
An ideal soap plant is one in which the process of soap making, from the melting out of the stock to the packing and shipping of the finished product, moves downward from floor to floor, since by this method it is possible to utilize gravitation rather than pumping liquid fats and fluid soaps. Convenience and economy are obtained by such an arrangement.
The various machinery and other equipment for soap manufacture are well known to those connected with this industry. It varies, of course, depending upon the kind of soap to be manufactured, and full descriptions of the necessary machinery are best given in the catalogs issued by the manufacturers of such equipment, who in this country are most reliable.
To know just what equipment is necessary can very easily be described by a brief outline of the process various soaps undergo to produce the finished article. After the saponification has taken place in thesoap kettlethe molten soap is run directly into the soapframes,which consist of an oblong compartment, holding anywhere from 400 to 1,200 pounds, with removable steel sides and mounted upon trucks, in which it solidifies. In most cases it is advisable to first run the soap into acrutcheror mixer which produces a more homogeneous mass than if this operation is omitted. Color and perfume may also be added at this point, although when a better grade of perfume is added it must be remembered that there is considerable loss due to volatilization of same. When adrying machineis employed the molten soap is run directly upon the rollers of this machine, later adding about 1.0% zinc oxide to the soap from which it passes continuously through the drying chamber and is emitted in chip form ready for milling. After the soap has been framed, it is allowed to cool and solidify, which takes several days, and then the sides of the frame are stripped off. The large solid cake is cut with wires by hand or by aslabberinto slabs of any desired size. These slabs are further divided into smaller divisions by thecutting table. In non-milled soaps (laundry soaps, floating soaps, etc.), these are pressed at this stage, usually by automatic presses, after a thin hard film has been formed over the cake by allowing it to dry slightly. In making these soaps they are not touched by hand at any time during the operation, the pressing, wrapping and packing all being done by machinery. For a milled soap the large slabs are cut into narrow oblong shapes by means of the cutting table to readily pass into the feeder of thechipper, the chips being spread upontraysand dried in adry houseuntil the moisture content is approximately 15%.
The process of milling is accomplished by passing the dried soap chips through asoap mill, which is a machine consisting of usually three or four contiguous, smooth,granite rollers operated by a system of gears and set far enough apart to allow the soap to pass from a hopper to the first roller, from which it is constantly conveyed to each succeeding roller as a thin film, and finally scraped from the last roller to fall into themilling boxin thin ribbon form. These mills are often operated in tandem, which necessitates less handling of soap by the operator. The object of milling is to give the soap a glossy, smooth finish and to blend it into a homogeneous mass. The perfume, color, medication or any other material desired are added to the dried soap chips prior to milling. Some manufacturers use anamalgamatorto distribute these uniformly through the soap, which eliminates at least one milling. When a white soap is being put through the mill, it is advisable to add from 0.5% to 1% of a good, fine quality of zinc oxide to the soap, if this substance has not been previously added. This serves to remove the yellowish cast and any translucency occasioned by plodding. Too great a quantity of this compound added, later exhibits itself by imparting to the soap a dead white appearance. Inasmuch as the milling process is one upon which the appearance of a finished cake of toilet soap largely depends, it should be carefully done. The number of times a soap should be milled depends upon the character of a soap being worked. It should of course be the object to mill with as high a percentage of moisture as possible. Should the soap become too dry it is advisable to add water directly, rather than wet soap, since water can more easily be distributed through the mass. As a general statement it may be said it is better policy to overmill a soap, rather than not mill it often enough.
After the soap has been thoroughly milled it is ready for plodding. Aplodderis so constructed as to take thesoap ribbons fed into the hopper by means of a worm screw and continuously force it under great pressure through a jacketed cylinder through which cold water circulates in the rear to compensate the heat produced by friction and hot water at the front, to soften and polish the soap which passes out in solid form in bars of any shape and size depending upon the form of theshaping platethrough which it is emitted. The bars run upon aroller board, are cut into the required length by a specialcake cutting table, allowed to dry slightly and pressed either automatically or by a foot powerpressin any suitable soapdie. The finished cake is then ready for wrapping and after due time in stock reaches the consumer.
Besides the various apparatus mentioned above there are many other parts for the full equipment of a modern soap plant, such as remelters, pumps, mixers, special tanks, power equipment, etc. As has been stated, however, practical experience will aid in judging the practicability as to installation of these. The various methods of powdering soap are, however, not generally known. Where a coarse powder is to be produced, such as is used for common washing powders, no great difficulty is experienced with the well known Blanchard mill. In grinding soap to an impalpable powder the difficulties increase. The methods adapted in pulverizing soaps are by means of disintegrators, pebble mills and chaser mills. The disintegrator grinds by the principle of attrition, that is, the material is reduced by the particles being caused to beat against each other at great velocity; a pebble mill crushes the substance by rubbing it between hard pebbles in a slowly revolving cylinder; the chaser mill first grinds the material and then floats it as a very fine powder above a curb of fixed height. The last method is particularly adapted for the finest of powder (140 mesh and over).
In the saponification of fats and oils to form soap through the agency of caustic alkalis, as has been stated, the sodium or potassium salts of the mixed fatty acids are formed. Sodium soaps are usually termed hard soaps, and potassium soaps soft. There are, however, a great many varieties of soaps the appearance and properties of which depend upon their method of manufacture and the oils or fats used therein.
The various methods adopted in soap making may be thus classified:
1. Boiling the fats and oils in open kettles by open steam with indefinite quantities of caustic alkali solutions until the finished soap is obtained; ordinarily namedfull boiled soaps. These may be sub-divided into (a) hard soaps with sodium hydrate as a base, in which the glycerine is recovered from the spent lyes; (b) hard soaps with soda as a base, in which the glycerine remains in the soap, e. g., marine cocoanut oil soaps; (c) soft potash soaps, in which the glycerine is retained by the soap.
2. Combining the required amount of lye for complete saponification of a fat therewith, heating slightly with dry heat and then allowing the saponification to complete itself. This is known as thecold process.
3. Utilizing the fatty acid, instead of the neutral fat, and combining it directly with caustic alkali or carbonate, which is incorrectly termedcarbonate saponification, since it is merely neutralizing the free fatty acid and thus is not a saponification in the true sense of the word. No glycerine is directly obtained by this method, as it isusually previously removed in the clearage of the fat by either the Twitchell or autoclave saponification method.
In the methods thus outlined the one most generally employed is the full boiled process to form a sodium soap. This method of making soap requires close attention and a knowledge which can only be obtained by constant practice. The stock, strength of lyes, heat, amount of salt or brine added, time of settling, etc., are all influencing factors.
The principles involved in this process are briefly these:
The fat is partly saponified with weak lyes (usually those obtained from a previous boiling in the strengthening change are used), and salt is added to grain the soap. The mass is then allowed to settle into two layers. The upper layer is partly saponified fat; the lower layer, or spent lye, is a solution of salt, glycerine, and contains any albuminous matter or any other impurity contained in the fat. This is known as thekillingor glycerine change. Strong lyes are now added and the fat entirely saponified, which is termed thestrengthening change. The mass is then allowed to settle and the fluid soap run off above the "nigre." This operation is called the finish orfinishingchange.
The method may be more fully illustrated by a concrete example of the method of manufacture of a tallow base:
Charge—Tallow88 per cent.Cocoanut oil10 per cent.Rosin w. w.2 per cent.Amount charge10 tons
About five tons of tallow and one ton of cocoanut oil are pumped or run into the soap kettle and brought to a boil with wet steam until it briskly comes through the hot fat. The caustic soda (strengthening lyes from formerboilings may be used here) is gradually added by the distributing pipe, any tendency to thicken being checked by the introduction of small quantities of brine ("salt pickle"). If the lye is added too rapidly the soap assumes a granular appearance, indicating that the addition of same must be discontinued. Water should then be added and the mass boiled through until it again closes. When the addition of the proper amount of caustic soda is nearing its completion the soap gradually thins. The steam is now cut down to about one turn of the valve, and brine is rapidly added or salt shoveled in. In ten to fifteen minutes the steam again breaks through and, from the appearance of the soap, it can be seen whether sufficient brine has been added. A sample taken out by means of a long wooden paddle should show the soap in fine grains with the lyes running from it clear. The steam is then shut off and the soap allowed to settle from one and one-half to two hours. In all settlings the longer time this operation is permitted to continue, the better will the subsequent operations proceed.
The mixture now consists of a partly saponified layer of fat above the spent lyes. The lyes are drawn off until soap makes its appearance at the exit pipe. The valve is then closed and the soap blown back into the kettle by steam. The lyes thus obtained are known asspent lyes, from which the glycerine is recovered. They should show an alkalinity of approximately 0.5 per cent. if the operation is carefully carried out.
The remaining tallow is now added and the above operations repeated.
After the spent lyes have been drawn off, the soap is closed with water and the proper percentage of rosin soap previously formed, or rosin itself is added to the mass in the kettle. More lye is then allowed to flow in until themixture is up to "strength." This is usually tested by the "bite" on the tongue of a small cooled sample. After boiling until the steam comes through, the mass is grained with salt as before and allowed to settle one and one-half to three hours. These lyes, known asstrengthening lyesare run to storage to be used subsequently with fresh fat to take up the caustic soda contained therein.
The soap is now ready for finishing and is first boiled through and tried for strength. A drop of phenolphthalein (1 per cent. phenolphthalein in 98 per cent. alcohol) is allowed to drop on the molten soap taken up on a trowel. The red color should be instantly produced and develop to a full deep crimson in a few seconds, or more lye must be added until this condition is realized. Should it flash a deep crimson immediately it is on the strong side. This cannot be conveniently remedied; it can only serve as a guide for the next boil, but in any case it is not of any serious consequence, unless it is too strong.
With the steam on, the soap is now examined with a trowel which must be thoroughly heated by working it about under the surface of the hot soap. The appearance of the soap as it runs from the face of the trowel indicates its condition. It is not possible to absolutely describe the effect, which can only be properly judged by practice, yet the following points may serve as a guide. The indications to be noticed are the shape and size of the flakes of soap as the sample on the trowel breaks up and runs from the hot iron surface, when the latter is turned in a vertical position, as well as the condition of the iron surface from which the soap flakes have fallen. A closed soap will run slowly into a homogeneous sheet, leaving the trowel's surface covered with a thin layer of transparent soap; a grained mass will run rapidly down in tiny grains, about one-half an inch in diameter or less, leaving the hot trowelabsolutely dry. The object of the finish is to separate the soaps of the lower fatty acids from those of the higher, and both from excess of liquid. A point midway between "open" and "closed" is required to arrive at this point.
Having arrived at the above condition, the soap is allowed to settle anywhere from one to three days and then run off through the skimmer pipes to the nigre and framed or pumped to the tank feeding the drying machine.
The stock thus obtained should be fairly white, depending upon the grade of tallow used and slightly alkaline to an alcoholic phenolphthalein solution. If removed at exactly the neutral point or with a content of free fat the soap will sooner or later develop rancidity. The soap thus obtained is an ordinary tallow base, and the one by far greatest used in the manufacture of toilet soaps. The percentage of cocoanut oil indicated is not fixed and may readily be varied, while in fine toilet soap the rosin is usually eliminated.
In the manufacture of full boiled soda soaps in which no glycerine is obtained as a by-product, it being retained in the soap itself, the soap formed is known as a "run" soap. The process is used most extensively in the manufacture of marine soaps by which the method may be best illustrated. This soap is known as marine soap because of its property of readily forming a lather with salt water and is mostly consumed aboard vessels.
Marine soaps are manufactured by first placing in the kettle a calculated amount of lye of 25 deg. to 35 deg. B., depending upon the amount of moisture desired in the finished soaps, plus a slight excess required to saponify a known weight of cocoanut oil. With open steam on, the cocoanut oil is then gradually added, care being taken that the soap does not froth over. Saponification takes place readily and when the oil is entirely saponified the finishedsoap is put through the process known as running. This consists in constantly pumping the mass from the skimmer pipe back into the top of the kettle, the object being to prevent any settling of the nigre or lye from the soap, as well as producing a homogeneous mass. It is customary to begin the saponification in the morning, which should be completed by noon. The soap is then run for about three hours and framed the next morning. After having remained in the frame the time required to solidify and cool, the soap is slabbed and cut into cakes. This process is difficult to carry out properly, and one not greatly employed, although large quantities of marine soap are purchased by the government for use in the navy and must fulfill certain specifications required by the purchasing department.
In making potash soaps it is practically impossible to obtain any glycerine directly because of the pasty consistency of the soap, and no graining is possible because the addition of salt to a soft soap, as already explained, would form a soda soap. Large quantities of soft soaps are required for the textile industries who desire mostly a strong potash soap, and the large number of automobiles in use at the present time has opened a field for the use of a soft soap for washing these. A soap for this purpose must be neutral so as not to affect the varnish or paint of automobiles.
A suitable soap for textile purposes may be made as follows:
Red oil80partsHouse grease20partsCaustic soda lye, 36 degs. B.3partsCarbonate of potash5-1/2partsCaustic potash23-1/4parts
Olive oil, corn oil, soya bean oil, olive oil foots or cottonseedoil may replace any of the above oils. A large quantity of cottonseed oil will cause the soap to fig.
To carry out the process, the caustic potash and carbonate of potash are dissolved and placed in the kettle together with the soda lye, and the oils added. This is most satisfactorily accomplished by being finished the day before the boiling is begun. The next day the boiling is begun and water added to bring the soap up to the desired percentage of fatty acid, due allowance being made for the water formed by the condensation of the open steam in boiling. Care must be taken that the soap in the kettle does not swell and run over during the saponification. A good procedure is to use open steam for a period of about two hours, then close the valve and allow the saponification to continue without boiling, and repeat this until it is entirely saponified. After the saponification has been completed the soap is briskly boiled all day and the proper corrections made; that is, if too alkaline, more oil is added, and if free fat is present, more potash. About 2 per cent. carbonate of potash is the proper amount for a soap containing 50 per cent. fatty acid. The soap is sampled by allowing it to drop on a clean, cold glass surface. In so doing, the soap should not slide or slip over the glass surface when pressed thereon, but should adhere to the glass, or it is too alkaline. A sample worked between the fingers showing too much stringiness should have more strong potash and oil added. A sample taken out in a pail and allowed to cool over night will serve as a guide as to the body of the soap in the kettle. When the soap has thus been properly finished it is run into barrels.
For an automobile soap the following is a good working formula: