Glue And Gelatine Substitutes
( Originally Published 1906 )
WHERE adhesiveness is the chief end to be attained, proteid substances other than glue, as well as a number of vegetable products, may be used in the place of glue. Certain algae gelatinize from solution and hence are available as substitutes for gelatine in some classes of work. At times these products are substituted with-out the purchaser's knowledge; at others, he knowingly selects them in the belief that they are cheaper than glue. It is to be borne in mind that they are avail-able as glue substitutes only 'for the purpose of adhesion, and even then they are not as economical, in actual work, as glue, although they possess some of the characteristics of the latter. In certain industries, notably in the manufacture of paper boxes, it is desirable to employ an adhesive which, while it binds, does not jell. Hence the use of such agglutinants as "Liquid Glue" and "Boston Gum," both of which may be used cold on the topping-machine. The use of glue substitutes in such case is not open to adverse comment. On the other hand, the abuse of the purchaser's credulity to the extent of offering dextrine or gum crystals as glue is to be condemned.
In the early days of the glue industry, it was a common practice to adulterate ground glues with rosin.
Sand was also used to a limited extent; and it is the "recollection of these practices, long since abandoned, that actuates 90 per cent of latter-day prejudice against ground and powdered glue. A more modern attempt at adulteration is the endeavor to combine corn dextrine with ground glue. The dextrine is first dissolved, the solution evaporated to driness, and the resultant product ground and mixed with the glue. In times of glue scarcity, when the price of all grades is abnormally high, the consumer naturally turns to some cheaper product that will answer his requirement; and it is in this way that the majority of glue substitutes have come into use.
Casein. — When the sugar of milk ferments, producing lactic acid, the milk turns sour, and casein, the characteristic proteid of milk, is separated in a coagulated mass. The entire phenomenon is due to the action of the Bacterium Lactis. Casein is also produced when acetic acid is added to fresh milk, if this be diluted and warmed. Exact neutralization with acid does not precipitate the casein owing to the interference of the alkaline phosphates present in the milk. An appreciable excess of acid must be employed.
A somewhat modified form of casein is obtained by the treatment of milk with rennet, a ferment extracted from the fourth stomach of the sucking calf. This contains the enzyme rennin or chymose, which coagulates the milk, the casein separating and the milk-sugar, lactalbumins, etc., remaining in solution. The casein so obtained differs from that produced by the addition of acid to the milk, in that the latter form is a precipitate which, under suitable conditions, can again be obtained in solution; whereas the action of the rennet is true coagulation and the casein is insoluble in any media save such as change its chemical constitution.
Commercial casein is purified by alternate solution in alkali and precipitation with acid, the precipitate being thoroughly washed each time. The number of these treatments determines its purity and hence its price. According to purity, the color of the dry product varies from brownish-yellow to almost white. Casein is insoluble in cold water (1 part to 1000), and in hot water swells to a sticky paste without undergoing real solution. It is readily soluble in weak alkalies and weak acids. To facilitate solution, casein is frequently mixed with 12 per cent of borax, the mixture coming into the market under the name Soluble Casein. Caustic alkalies exercise a drastic action on casein, deepening the color of the solution and imparting a disagreeable odor.
The application of casein to the arts is varied. It is useful as a substitute for albumin in calico printing. Upon evaporation from ammoniacal solution, casein is only. partially soluble in alkalies, and if the solution of casein in ammonia be treated with milk of lime, the casein, upon evaporation of the solution, is fast to all washing and soaping. Dolfus converts the casein into a nitro-compound, and this is dissolved with the aid of caustic soda, the consistency of the solution being reduced with water. When steamed, this becomes fixed in the cloth, resisting the action of soaping and chlorine.
Casein is applied as the thickener for gold and aluminum bronzes for printing silk. It is far cheaper than gum tragacanth, and yields even better results.
An insoluble compound results from the treatment of casein with slaked lime. This combination is useful as a cement for earthenware, etc. A water-proofing compound is obtained by treating solutions of casein with formaldehyde. A small amount of formaldehyde suffices to produce the desired result, any excess precipitating the casein from solution.
Casein is of service in the preparation of colored micas for printing wall-paper. The aniline color is precipitated upon the mica by some suitable reagent and the addition to the solution (hot) of a small quantity of casein serves to bind the color firmly to the mica. In the same industry, casein may be wholly substituted for glue as the medium for sizing the pulp colors. Its use for this purpose is attended by difficulty, inasmuch as certain of the colors, when in combination with the casein, cause the latter to ferment, the mixed color and size frequently overflowing the barrel.
Very serviceable insoluble lakes or pulp-colors may be prepared by precipitating casein from ammoniacal solution in conjunction with the color, by means of chloride of aluminium, stannous chloride or acetate.
Egg- and Blood-Albumin. — The albumin of eggs is distinguished from that of blood-serum, etc., by the designation ALBUMEN. White of egg is a nearly pure solution of proteids, the chief of which is egg-albumin or ALBUMEN. Upon evaporation at 60° C., white of egg yields about 14 per cent of albuminous residue. If the white of egg is thoroughly beaten with water, the albumin and salts pass into solution, membraneous material remaining behind. The albumin may be separated from the soluble salts by precipitation with basic acetate of lead, the precipitate decomposed with carbonic acid, and the lead removed with sulphuretted hydrogen. Coagulation occurs upon cautiously warming the liquid to 60° C., the first flakes of albumin carrying down with them the last traces of lead sulphide, leaving the supernatant liquid colorless. This is evaporated at 35° C., when the albumen is obtained in pale yellow scales. (Allen.)
Albumen may be obtained in the solid state by cautiously evaporating white of egg at a temperature below 50° C. It is fairly transparent and of a pale yellow color. It is frequently adulterated owing to the fact that it is more valuable than blood-albumin.
Blood- or serum-albumin results from the evaporation of the separated serum of perfectly fresh blood. The evaporation is conducted at about 50° C., when the albumin is obtained in the form of scales or flakes varying in color from grayish to black. Three or four qualities of blood-albumin are known, the purest being a dirty yellow, and the poorest, black.
Both egg- and blood-albumin are applied to the printing of cotton fabrics, when they are rendered insoluble by coagulation with steam, acting as mordants for a number of colors. Egg-albumin is also employed in silk printing as one of the ingredients of the color-thickener. It finds further application in the manufacture of confectionery. Black blood-albumin is not used for printing fabrics, but is useful in sugar-refining and in dyeing with Turkey-red. Blood-albumin may be employed for printing all but the most delicate colors. It is cheaper than egg-albumin and has greater thickening power. Egg-albumin is largely substituted for gelatine in photography in the preparation of sensitive coatings for printing-papers, which consist of albumen treated with silver haloids. The author has frequently been called upon for an opinion respecting "glue," which has turned out to be nothing more than blood-albumin and sometimes egg-. It is difficult to understand how one could be inveigled into the purchase of albumin for glue, the characteristic odor of the former being sufficient to distinguish the two, as well as being so disagreeable as to bar it from many uses to which glue is adapted.
Dextrine Crystals. Dextrines result from the treatment of the corresponding starches with acids at various temperatures, the duration of the treatment determining the color as well as the solubility of the product. The best are those produced from potato starch, and in order of serviceability rank tapioca-dextrines, corn-dextrines and sago-dextrines. British gum is made from the various starches by simply roasting these for a certain length of time without the aid of acid. Its solution is heavier in body than those of dextrines, and is much lighter in color.
Canary potato-dextrine is of medium yellow color in solution, which, if prepared sufficiently concentrate, yields dark yellow crystals closely resembling the particles of a ground foreign glue of light shade. These require preliminary softening or soaking prior to solution, and this is similar in appearance and characteristics to the solutions of weak animal glue, with the exception, of course, that the dextrine solution does not jell. Solutions of dextrine admirably fulfil the minor requirement of the paper-box maker, as they are as adhesive as weak glue. They have not equal binding strength, however, nor are they cheaper than glue, as many would believe. They are readily prone to de-composition and molding, unless properly preserved with formaldehyde or carbolic acid.
Gum Arabic. — This gum is too well known to require detailed description in these pages. It is extensively employed in the manufacture of mucilages, in conjunction with dextrines. The poorer varieties are some-times substituted for glue. The particles of gum require long soaking before applying heat to bring them into solution, and the solution must be prepared very thick to equal in adhesiveness that of a weak glue. Under these circumstances, the gum is more costly than animal glue. The addition of some glycerine is necessary to impart sufficient flexibility to the dried gum.
Japanese Gelatine, etc. Certain alge e or sea-weeds yield a highly gelatinous substance upon treatment with boiling water. Chief among these is the Gelideum Corneum, familiarly known as Chinese Moss or Japanese Gelatine. Its chief constituent is gelose, which has ten times the gelatinizing power of isinglass, setting to a jelly when dissolved in five hundred times its weight of water. It occurs in commerce in bundles of long strips and resembles some forms of isinglass. It swells in cold water and is thoroughly soluble in hot. Upon cooling, the solution sets to a jelly which, al-though its melting point is higher than that of isinglass, lacks tenacity. The jelly is colorless and translucent, like that of a high-grade gelatine.
Chondrus crispus, Irish Moss, is an alga gathered from the rocks at low tide on the west coast of Ireland, where it constitutes an article of diet. The greater part of the moss consists of the gelatinous substance, carrageenin, somewhat analogous to gelose, though yielding a far darker jelly. The jelly finds application in medicine and is also used in the manufacture of textile fabrics, either as a finishing size or as a thickening medium for printing colors on cotton or silk.
Agar- Agar, the edible sea-weed of Ceylon and other localities, contains a gelatinous principle very similar to gelose.
Gluten. — Starch-tailings, consisting mainly of gluten, or the latter itself, are the basis of the so-called dry pastes which are offered in place of regular flour-paste; and this substance is worthy of some consideration as a possible glue substitute. Wheat flour consists of starch and gluten, the latter containing the two proteids, glutenin and gliadin. When flour is kneaded in a bag under a stream of water, the starch gradually passes into solution and the gluten remains behind as a brownish, sticky mass. This dries to a grayish, brittle sub-stance which, though insoluble in cold water, is fairly soluble in boiling, the undissolved portions combining with those in solution to produce an extremely heavy, sticky paste. Solution of the dried gluten is facilitated by the addition of a small amount of alkali, and the gray color of the dried product is improved and whitened by the addition of chalk, silver white, and possibly a trace of ultramarine blue.
Though somewhat more troublesome of manipulation than ready-prepared flour-paste, "dry" pastes are far more adhesive, owing to the greater content of gluten. The serviceability of regular flour-pastes is largely dependent upon the proper development of the gluten of the flour. By treatment with a small amount of borax, cooking at a proper temperature, a flour-paste may be produced which is fully the equal, if not the superior, of weak glues in binding as well as adhesion. The author has seen such pastes bind two sticks of wood so that considerable force was necessary to break them apart; in one instance, the wood breaking before the cemented joint gave way. Flour-pastes, well made, regular or "dry," have largely supplanted glue in trunk-making as well as the production of leather novelties, such as bags, belts, and pocket-books. The heavy canvas covering of trunks is often laid on with good paste, which holds just as well as a medium quality of glue, and is far cheaper and easier of manipulation, requiring no preliminary soaking.
Gluten has, of course, its disadvantages in use. It is prone to rapid decomposition and putrefaction, the gases evolved being of the most unpleasant character. The problem of a proper preservative for flour-paste remains unsolved. Mercuric chloride is commonly employed, in solution in hydrochloric acid. Hydrofluoric acid works well as does also formaldehyde, though the pungent odor of the latter is a decided disadvantage.
"Liquid Glue." — This is used in the manufacture of paper boxes, in conjunction with flour-paste, for the lighter work. It contains no animal glue whatsoever, being a solution of British gum and light and dark canary corn-dextrine. To this, flour-paste is at times added with a view to increasing the "body" of the solution. "Liquid Glue" is dark brown in color and dries not unlike a solution of a weak, dark bone glue. Properly prepared, it is fairly adhesive in solution and is preserved with cresylic acid (crude "carbolic" acid), formaldehyde, etc., an essential oil being frequently added to disguise the odors of the preservatives.
Boston Gum. — A solution of dextrines, blackish in color owing to the admixture of crude phenol or cresylic acid as a preservative, is employed by some paper-box manufacturers in preference to "liquid glue." It is extremely useful for "topping," as it may be run cold on the machine for this work. It excels "liquid glue" in adhesiveness and resembles more closely than the latter a solution of weak animal glue. It has also the advantage in that it does not impair the gloss of the paper, as do many preparations of superior adhesiveness and binding power, which are made by bringing starches into solution in the cold with the aid of caustic alkali. These latter invariably dry to a dull coating.
Preparations such as Brightwood gum, envelope gum and similar dextrine pastes or solutions are now used exclusively in the manufacture of envelopes where formerly glue was employed.
Methods of Detection and Analysis. — Not only are some of the above-described products substituted for glue, but several of them are liable to adulteration. This applies particularly to commercial albumin, especially egg, which is hocused to a great extent by the unscrupulous.
In general, casein may be distinguished from albumins and all from genuine glue, by their characteristic odors. The odor of casein, whether dry or in solution, is markedly cheesy — a characteristic never observed in glue. The odor of albumin, while impossible of description, is easy of recognition, and once known is not easily forgotten. Solutions of dextrine are sweet to the taste and smell, unless these characteristics have been destroyed by preservatives. Gluten has an odor, when dry, not unlike that of stale crackers. In the wet state it preserves this same odor and is further recognizable from its consistency and appearance, which resembles that of an exceedingly dirty flour dough.
Casein. Though casein itself is not liable to adulteration, it may be employed to adulterate glue or - albumen. Solutions of casein are not coagulated by boiling, while those of albumins are. The casein may be precipitated from solution by an excess of common salt, magnesium sulphate, chloride of barium, and calcium. It is completely precipitated by the usual reagents for proteids sulphate of copper, bichloride of mercury, acetate of lead, etc.
When present in conjunction with glue, the casein may be separated by precipitating both with alcohol and boiling the precipitate, which coagulates the casein, rendering it insoluble. The precipitated glue may be then taken up with hot water.
Egg- and Blood-Albumin. Egg-albumin is usually translucent and of a pale yellow color. It should be free from blisters which are the evidence of imperfect coagulation. All commercial albumen of good quality should be free from any suggestion of the odors of putrefaction and unpleasant taste. On treatment with cold water and constant stirring, it should dissolve without leaving any residue.
Albumin is frequently adulterated with gelatine, sugar, dextrine, and even flour. For its examination, Allen proposes the following method which has yielded the author uniformly successful results:
Five grams of the powdered sample are treated with 50 c. c. of cold water and stirred frequently until all soluble matters are in solution. Pure samples leave no residue. A few drops of acetic acid are added and any insoluble residue filtered off through silk or fine muslin. This may consist of coagulated albumin, casein, starch, or membranous matter. The casein may be dissolved out by treatment with very dilute caustic soda and precipitated by exact neutralization with acetic acid. The aqueous solution of the sample is now boiled, when the albumin is thrown down as a flocculent precipitate which may be filtered off, washed, and weighed; or treated by Kjeldahl's process and the albumin deduced from the ammonia obtained. The filtrate from the albumin is treated with acetic acid and potassium ferrocyanide, to make sure that all the albumin has been precipitated. Any organic, precipitate produced by this treatment will consist of casein. Zinc, which may have been added to increase the thickening power, will be thrown down at this juncture as white ferrocyanide. If no proteid remain in solution, gelatin may be precipitated by the addition of tannin, the liquid filtered and concentrated to small bulk, when any gum or dextrine will be precipitated by treatment with alcohol. Sugar, if present, will remain in solution with the alcohol and may be detected by boiling off the alcohol, heating the liquid with hydrochloric acid, and treating with Fehling's solution. Sugar might also be extracted by treating the original dry sample with alcohol.
For the assay of commercial albumin, Ziegler dissolves 20 grams of the sample in 100 c. c. cold water. The solution is strained through a sieve and 10 c. c. of the clarified solution is added to a boiling 20 per cent solution of alum. The appearance and volume of the coagulum is noted, and then it is washed, dried, and weighed. With pure albumin the results are very good and their accuracy is not affected by the presence of dextrine. Gum arabic, however, interferes seriously with the precipitation of the albumin. (De Koninck.)
Blood- and egg-albumin may be distinguished from each other by the following reactions:
Solutions of blood-albumin in which are present the ordinary salts are unaffected by agitation with ether, whereas egg-albumin is coagulated. If in dilute solution the precipitate appears at the junction of the layers of ether and water. It is to be observed that if no salts are present this behavior is reversed, the blood-albumin being precipitated while the egg- remains unaffected.
Blood-albumin is readily soluble in concentrated nitric acid, while egg-albumin is only sparingly soluble in this medium.
Dextrine Crystals. The active constituent of dextrines may be designated as dextrin. Chemically, this product is intermediate between starch and grape-sugar.
Its empirical formula alone is known, and is (C6H1005)n, that is, some multiple of the starch formula C6 H10 O5. If the process of dextrinization, i.e., the treatment of a starch with a trace of nitric acid with the aid of heat, be prolonged, the starch is first converted into dextrin and subsequently into grape-sugar, C6 H12 O6. The conversion of starch into dextrin, and, subsequently, of dextrin into grape-sugar, may therefore be assumed to be that of hydrolysis and may roughly be stated by the equation, C6 H10 O5 + H2O = C6 H12 O6.
Commercial dextrine must be regarded as a mixture of unconverted starch, dextrin, and grape-sugar. The further conversion is carried, the more soluble the product, the deeper the shade of its solution, and the greater the quantity of grape-sugar present. Dextrines are sometimes produced by the action of malt-infusion upon solutions of starch, the diastase of the malt converting the starch first into dextrin and ultimately into the sugar, maltose. The temperature of the operation should never exceed 60° F.
Both levulose and maltose reduce Fehling's solution, and hence if the solution of agglutinant be suspected to be dextrine, this may readily be recognized. This test is applicable to the detection of "Liquid Glue" or Boston Gum, although the general appearance and characteristics of these serve to identify them in the majority of instances.
Japanese Gelatine, etc. — These will be recognized by the form in which they appear in commerce, the long, slender strips resembling only a certain form of isinglass, and the difference in the characters of the jelly will soon differentiate them from the latter.