Soap-Making Manual Part 16

The stills are usually built of copper, which are heated by both direct fire and superheated steam. Distillation under vacuum is advisable. To begin the distilling operation, the still is first filled with dry hot fatty acids to the proper level. Superheated steam is then admitted and the condenser is first heated to prevent the freezing of the fatty acids, pa.s.sing over into same. When the temperature reaches 230 deg. C.

the distillation begins. At the beginning, the fatty acids flow from the condenser, an intense green color, due to the formation of copper soaps produced by the action of the fatty acids on the copper still. This color may easily be removed by treating with dilute acid to decompose the copper soaps.

In vacuum distillation, the operation is begun without the use of vacuum. Vacuum is introduced only when the distillation has proceeded for a time and the introduction of this must be carefully regulated, else the rapid influence of vacuum will cause the contents of the still to overflow. When distillation has begun a constant level of fatty acids is retained therein by opening the feeding valve to same, and the heat is so regulated as to produce the desired rate of distillation. As soon as the distillate flows darker and slower, the feeding valve to the still is shut off and the distillation continued until most of the contents of the still are distilled off, which is indicated by a rise in the temperature. Distillation is then discontinued, the still shut down, and in about an hour the contents are sufficiently cool to be emptied.

The residue is run off into a proper receiving vessel, treated with dilute acid and used in the distillation of tar.

In the distillation of tar the same method as the above is followed, only distillation proceeds at a higher temperature. The first portion and last portion of the distillate from tar are so dark that it is necessary to add them to a fresh charge of fatty acids. By a well conducted distillation of tar about 50 per cent. of the fatty acids from the tar can be used to mix with the distilled fatty acids. The residue of this operation called stearine pitch or candle tar consists of a hard, brittle, dark substance. Elastic pitch only results where distillation has been kept constant for several days without interrupting the process, and re-distilling the tar. In a good distillation the distillation loss is 0.5 to 1.5% and loss in pitch 1.5%. Fatty acids which are not acidified deliver about 3% of pitch.

Very impure fats yield even a higher percentage in spite of acidifying.

For a long time it was found impossible to find any use for stearine pitch, but in recent years a use has been found for same in the electrical installation of cables.

FOOTNOTES:

[12] Journ. Ind. Eng. Chem. (1909), I, p. 654.

CHAPTER VI

a.n.a.lytical Methods.

While it is possible to attain a certain amount of efficiency in determining the worth of the raw material entering into the manufacture of soap through organoleptic methods, these are by no means accurate. It is, therefore, necessary to revert to chemical methods to correctly determine the selection of fats, oil or other substances used in soap making, as well as standardizing a particular soap manufactured and to properly regulate the glycerine recovered.

It is not our purpose to cover in detail the numerous a.n.a.lytical processes which may be employed in the examination of fats and oils, alkalis, soap and glycerine, as these are fully and accurately covered in various texts, but rather to give briefly the necessary tests which ought to be carried out in factories where large amounts of soap are made. Occasion often arises where it is impossible to employ a chemist, yet it is possible to have this work done by a competent person or to have someone instruct himself as just how to carry out the more simple a.n.a.lyses, which is not a very difficult matter. The various standard solutions necessary to carrying out the simpler t.i.trations can readily be purchased from dealers in chemical apparatus and it does not take extraordinary intelligence for anyone to operate a burette, yet in many soap plants in this country absolutely no attention is paid to the examining of raw material, though many thousand pounds are handled annually, which, if they were more carefully examined would result in the saving of much more money than it costs to examine them or have them at least occasionally a.n.a.lyzed.

a.n.a.lYSIS OF FATS AND OILS.

In order to arrive at proper results in the a.n.a.lysis of a fat or oil, it is necessary to have a proper sample. To obtain this a sample of several of the packages of oil or fat is taken and these mixed or molten together into a composite sample which is used in making the tests. If the oil or fat is solid, a tester is used in taking the sample from the package and if they are liquid, it is a simple matter to draw off a uniform sample from each package and from these to form a composite sample.

In purchasing an oil or fat for soap making, the manufacturer is usually interested in the amount of free fatty acid contained therein, of moisture, the t.i.ter, the percentage of unsaponifiable matter and to previously determine the color of soap which will be obtained where color is an object.

DETERMINATION OF FREE FATTY ACIDS.

Since the free fatty acid content of a fat or oil represents a loss of glycerine, the greater the percentage of free fatty acid, the less glycerine is contained in the fat or oil, it is advisable to purchase a fat or oil with the lower free acid, other properties and the price being the same.

While the mean molecular weight of the mixed free fatty acids varies with the same and different oils or fats and should be determined for any particular a.n.a.lysis for accuracy, the free fatty acid is usually expressed as oleic acid, which has a molecular weight of 282.

To carry out the a.n.a.lysis 5 to 20 grams of the fat are weighed out into an Erlenmeyer flask and 50 cubic centimeters of carefully neutralized alcohol are added. In order to neutralize the alcohol add a few drops of phenolphthalein solution to same and add a weak caustic soda solution drop by drop until a very faint pink color is obtained upon shaking or stirring the alcohol thoroughly. The mixture of fat and neutralized alcohol is then heated to boiling and t.i.trated with tenth normal alkali solution, using phenolphthalein as an indicator. As only the free fatty acids are readily soluble in the alcohol and the fat itself only slightly mixes with it, the flask should be well agitated toward the end of the t.i.tration. When a faint pink color remains after thoroughly agitating the flask the end point is reached. In order to calculate the percentage of free fatty acid as oleic acid, multiply the number of cubic centimeters of tenth normal alkali used as read on the burette by 0.0282 and divide by the number of grams of fat taken for the determination and multiply by 100.

When dark colored oils or fats are being t.i.trated it is often difficult to obtain a good end point with phenolphthalein. In such cases about 2 cubic centimeters of a 2 per cent. alcoholic solution of Alkali Blue 6 B is recommended.

Another method of directly determining the free fatty acid content of tallow or grease upon which this determination is most often made is to weigh out into an Erlenmeyer flask exactly 5.645 grams of a sample of tallow or grease. Add about 75 cubic centimeters of neutralized alcohol.

Heat until it boils, then t.i.trate with tenth normal alkali and divide the reading by 2, which gives the percentage of free fatty acid as oleic. If a fifth normal caustic solution is used, the reading on the burette gives the percentage of free fatty acid directly. This method, while it eliminates the necessity of calculation, is troublesome in that it is difficult to obtain the exact weight of fat.

MOISTURE.

To calculate the amount of moisture contained in a fat or oil 5 to 10 grams are weighed into a flat bottom dish, together with a known amount of clean, dry sand, if it is so desired. The dish is then heated over a water bath, or at a temperature of 100-110 degs. C., until it no longer loses weight upon drying and reweighing the dish. One hour should elapse between the time the dish is put on the water bath and the time it is taken off to reweigh. The difference between the weight of the dish is put on the water bath and the time it is taken off when it reaches a constant weight is moisture. This difference divided by the original weight of the fat or oil 100 gives the percentage of moisture.

When highly unsaturated fats or oils are being a.n.a.lyzed for moisture, an error may be introduced either by the absorption of oxygen, which is accelerated at higher temperature, or by the formation of volatile fatty acids. The former causes an increase in weight, the latter causes a decrease. To obviate this, the above operation of drying should be carried out in the presence of some inert gas like hydrogen, carbon dioxide, or nitrogen.

t.i.tER.

The t.i.ter of a fat or oil is really an indication of the amount of stearic acid contained therein. The t.i.ter, expressed in degrees Centigrade, is the solidification point of the fatty acids of an oil or fat. In order to carry out the operation a Centigrade thermometer graduated in one or two-tenths of a degree is necessary. A thermometer graduated between 10 degs. centigrade to 60 degs. centigrade is best adapted and the graduations should be clear cut and distinct.

To make the determination about 30 grams of fat are roughly weighed in a metal dish and 30-40 cubic centimeters of a 30 per cent. (36 degs.

Baume) solution of sodium hydroxide, together with 30-40 cubic centimeters of alcohol, denatured alcohol will do, are added and the ma.s.s heated until saponified. Heat over a low flame or over an asbestos plate until the soap thus formed is dry, constantly stirring the contents of the dish to prevent burning. The dried soap is then dissolved in about 1000 cubic centimeters of water, being certain that all the alcohol has been expelled by boiling the soap solution for about half an hour. When the soap is in solution add sufficient sulphuric acid to decompose the soap, approximately 100 cubic centimeters of 25 degs.

Baume sulphuric acid, and boil until the fatty acids form a clear layer on top of the liquid. A few pieces of pumice stone put into the mixture will prevent the b.u.mping caused by boiling. Siphon off the water from the bottom of the dish and wash the fatty acids with boiling water until free from sulphuric acid. Collect the fatty acids in a small ca.s.serole or beaker and dry them over a steam bath or drying oven at 110 degs.

Centigrade. When the fatty acids are dry, cool them to about 10 degs.

above the t.i.ter expected and transfer them to a t.i.ter tube or short test tube which is firmly supported by a cork in the opening of a salt mouth bottle. Hang the thermometer by a cord from above the supported tube so it reaches close to the bottom when in the t.i.ter tube containing the fatty acids and so that it may be used as a stirrer. Stir the ma.s.s rather slowly, closely noting the temperature. The temperature will gradually fall during the stirring operation and finally remain stationary for half a minute or so then rise from 0.1 to 0.5 degs. The highest point to which the mercury rises after having been stationary is taken as the reading of the t.i.ter.

DETERMINATION OF UNSAPONIFIABLE MATTER.

In order to determine the unsaponifiable matter in fats and oils they are first saponified, then the unsaponifiable, which consists mainly of hydrocarbons and the higher alcohols cholesterol or phytosterol, is extracted with ether or petroleum ether, the ether evaporated and the residue weighed as unsaponifiable.

To carry out the process first saponify about 5 grams of fat or oil with an excess of alcoholic pota.s.sium hydrate, 20-30 cubic centimeters of a 1 to 10 solution of pota.s.sium hydroxide in alcohol until the alcohol is evaporated over a steam bath. Wash the soap thus formed into a separatory funnel of 200 cubic centimeters capacity with 80-100 cubic centimeters water. Then add about 60 cubic centimeters of ether, petroleum ether or 86 degs. gasoline and thoroughly shake the funnel to extract the unsaponifiable. Should the two layers not separate readily, add a few cubic centimeters of alcohol, which will readily cause them to separate. Draw off the watery solution from beneath and wash the ether with water containing a few drops of sodium hydrate and run to another dish. Pour the watery solution into the funnel again and repeat the extraction once or twice more or until the ether shows no discoloration.

Combine the ether extractions into the funnel and wash with water until no alkaline reaction is obtained from the wash water. Run the ether extract to a weighed dish, evaporate and dry rapidly in a drying oven.

As some of the hydrocarbons are readily volatile at 100 degs.

Centigrade, the drying should not be carried on any longer than necessary. The residue is then weighed and the original weight of fat taken divided into the weight of the residue 100 gives the percentage unsaponifiable.

TEST FOR COLOR OF SOAP.

It is often desirable to determine the color of the finished soap by a rapid determination before it is made into soap. It often happens, especially with the tallows, that a dark colored sample produces a light colored soap, whereas a bleached light colored tallow produces a soap off shade.

To rapidly determine whether the color easily washes out of the tallow with lye, 100 cubic centimeters of tallow are saponified in an enameled or iron dish with 100 cubic centimeters of 21 degs. Baume soda lye and 100 cubic centimeters of denatured alcohol. Continue heating over a wire gauze until all the alcohol is expelled and then add 50 cubic centimeters of the 21 degs. Baume lye to grain the soap. Allow the lyes to settle and with an inverted pipette draw off the lyes into a test tube or bottle. Close the soap with 100 cubic centimeters of hot water and when closed again grain with 50 cubic centimeters of the lye by just bringing to a boil over an open flame. Again allow the lyes to settle and put aside a sample of the lye for comparison. Repeat the process of closing, graining and settling and take a sample of lye. If the lye is still discolored repeat the above operations again or until the lye is colorless. Ordinarily all the color will come out with the third lye.

The soap thus obtained contains considerable water which makes it appear white. The soap is, therefore, dried to about 15 per cent. moisture and examined for color. The color thus obtained is a very good criterion as to what may be expected in the soap kettle.

By making the above a.n.a.lyses of fats or oils the main properties as to their adaptability for being made into soap are determined. In some cases, especially where adulteration or mixtures of oils are suspected, it is necessary to further a.n.a.lyze same. The methods of carrying out these a.n.a.lyses are fully covered by various texts on fats and oils and we will not go into details regarding the method of procedure in carrying these out.

TESTING OF ALKALIS USED IN SOAP MAKING.

The alkalis entering into the manufacture of soap such as caustic soda or sodium hydroxide, caustic potash or pota.s.sium hydrate, carbonate of soda or sodium carbonate, carbonate of potash or pota.s.sium carbonate usually contain impurities which do not enter into combination with the fats or fatty acids to form soap. It is out of the question to use chemically pure alkalis in soap making, hence it is often necessary to determine the alkalinity of an alkali. It may again be pointed out that in saponifying a neutral fat or oil only caustic soda or potash are efficient and the carbonate contained in these only combines to a more or less extent with any free fatty acids contained in the oils or fats.

Caustic soda or potash or lyes made from these alkalis upon exposure to the air are gradually converted into sodium or pota.s.sium carbonate by the action of the carbon dioxide contained in the air. While the amount of carbonate thus formed is not very great and is greatest upon the surface, all lyes as well as caustic alkalis contain some carbonate.

This carbonate introduces an error in the a.n.a.lysis of caustic alkalis when accuracy is required and thus in the a.n.a.lysis of caustic soda or potash it is necessary to remove the carbonate when the true alkalinity as sodium hydroxide or pota.s.sium hydroxide is desired. This may be done by t.i.tration in alcohol which has been neutralized.

In order to determine the alkalinity of any of the above mentioned alkalis, it is first necessary to obtain a representative sample of the substance to be a.n.a.lyzed. To do this take small samples from various portions of the package and combine them into a composite sample.

Caustic potash and soda are hygroscopic and samples should be weighed at once or kept in a well stoppered bottle. Sodium or pota.s.sium carbonate can be weighed more easily as they do not rapidly absorb moisture from the air.

To weigh the caustic soda or potash place about five grams on a watch gla.s.s on a balance and weigh as rapidly as possible. Wash into a 500 cubic centimeter volumetric flask and bring to the mark with distilled water. Pipette off 50 cubic centimeters into a 200 cubic centimeter beaker, dilute slightly with distilled water, add a few drops of methyl orange indicator and t.i.trate with normal acid. For the carbonates about 1 gram may be weighed, washed into a 400 cubic centimeter beaker, diluted with distilled water, methyl orange indicator added and t.i.trated with normal acid. It is advisable to use methyl orange indicator in these t.i.trations as phenolphthalein is affected by the carbon dioxide generated when an acid reacts with a carbonate and does not give the proper end point, unless the solution is boiled to expel the carbon dioxide. Litmus may also be used as the indicator, but here again it is necessary to boil as carbon dioxide also affects this substance. As an aid to the action of these common indicators the following table may be helpful:

_Color in _Color in _Indicator._ Acid Alkaline _Action of Solution._ Solution._ CO_{2}._

Methyl orange Red Yellow Very slightly acid Phenolphthalein Colorless Red Acid Litmus Red Blue Acid