Part 1 (1/2)
Soap-Making Manual.
by E. G. Thomssen.
PREFATORY NOTE.
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 a.n.a.lyses 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 cla.s.sify the methods and ill.u.s.trate 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 a.n.a.lytical methods which are of value to control the 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.
Ill.u.s.trations 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 ill.u.s.trations 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
CHAPTER I
Raw Materials Used in Soap Making.
Soap is ordinarily thought of as the common cleansing agent well known to everyone. In a general and strictly chemical sense this term is applied to the salts of the non-volatile fatty acids. These salts are not only those formed by the alkali metals, sodium and pota.s.sium, 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 polis.h.i.+ng 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 pota.s.sium 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 pota.s.sium hydroxide (caustic potash). Sodium soaps are always harder than pota.s.sium soaps, provided the same fat or oil is used in both cases.
The detergent properties of soap are due to the fact that it acts as an alkali regulator, that is, when water comes into contact with soap, it undergoes what is called hydrolytic dissociation. This means that it is broken down by water into other substances. Just what these substances are is subject to controversy, though it is presumed caustic alkali and the acid alkali salt of the fatty acids are formed.
OILS AND FATS.
There is no sharp distinction between fat and oil. By ”oil” the layman has the impression of a liquid which at warm 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 const.i.tuent part, these fatty acids. Hydrocarbon oils or paraffines, included in the term ”oil,” are thus useless in the process of soap-making, as far as entering into chemical combination with the caustic alkalis is concerned. The oils and fats which form soap are those which are a combination of fatty acids and glycerine, the glycerine being obtained as a by-product to the soap-making industry.
NATURE OF A FAT OR OIL USED IN SOAP MANUFACTURE.
Glycerine, 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._,
OH OR C_{3} H_{5} OH + 3 ROH = C_{3} H_{5} OR + 3 H_{2}O OH OR
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.