Ox-Gall
The Chemical Constituents of Ox-Gall
In the bile of every animal are two peculiar acids both containing nitrogen. One of them free of sulphur, the other containing it, both by boiling with acids and alkalis yield the same acid free of nitrogen, which is called cholic acid.
If these two acids be separated from each other in a chemical way we obtain glycocholic acid, an acid free of sulphur and the other taurocholic acid containing sulphur. The alkali salts contained in bile are quite soluble in water or alcohol but insoluble in ether. To produce it in a pure state mix the bile with as much animal coal, (spodium) so that finally, on evaporation in the water-bath a dry powder results, from which is drawn, by the use of absolute alcohol, the now colorless cholic acid esters, cholesterine, choline, lactic acid, etc. When ether containing a little water is added, the cholic acid esters are precipitated as colorless plaster-like masses and crystallize, when left in the fluid for some time.
The so-called crystallized bile is the final material for the preparation of acids. The acids of ox-gall have been investigated in the most thorough manner.
Glycocholic acid is obtained as a colorless precipitate from a watery solution of crystallized ox-gall, by adding dilute sulphuric acid until the fluid becomes flocculent, which after a while, especially, if the water contains a little ether, is changed into a voluminous ‘magma’ of fine white needles.
If collected upon a filter, these needles unite and form a lustrous felt.
Glycocholic acid is sparingly soluble in water but soluble in alcohol. It forms the principal constituent of bile, it reacts feebly with acid and tastes bitter-sweet. Taurocholic acid is found only in small quantities in ox-gall and has no important effect on the colors.
The Effect of Ox-Gall Upon Colors
By chemical analysis we have seen that glycocholic acid is the principal constituent of ox-gall and in combination with taurocholic acid, glycin, choline and lactic acid is soluble in water. On the other hand, when pure, it is soluble with difficulty and therefore is only of use to us when in combination with other acids, as it must combine intimately with water-colors.
The atomic weight of gall and the insolubility of pure glycocholic acid in water are the most valuable properties of it for the marbling colors.
The first gives to the colors the expanding power, the latter the adhesion to paper.
All the lower fatty acids, among which ox-gall may be numbered, possess properties similar to fatty bodies, namely a less atomic weight than water. They differ from fatty bodies in this, that they mix with water.
The expanding power and lightness of ox-gall are, consequently, peculiarities of equal value. Marbling size forms the base for the colors, which by the consistency of the glutinous mass and by the gall added to them are prevented from sinking to the bottom. They float like drops of oil upon the water and only differ from them by the fact that the colors will spread out on the size, while the drops of oil on the water are contracted to circular spots of small size. If a drop of oil were thrown upon the size it would spread out very quickly.
This purely physical occurrence is caused by the different weights of the bodies and the consistency of the size. The fatty bodies, which are much lighter than water, float upon it but the gravity of the drop itself prohibits its spreading out, as it sinks somewhat and is held together by it. It is different with the size; by the consistency of the glutinous mass the gravity of the drop is antagonized and as a result it flattens and spreads out.
As I have already mentioned the insolubility of glycocholic acid binds the color to the paper. To explain this I will mention a few examples; the saturated alum solution will cause glycocholic acid to curdle. If, therefore, we add to ox-gall which is basic the saturated solution of alum, a soft plaster-like mass is precipitated which consists of glycocholate of aluminium, insoluble in water. This chemical reaction explains the durability of the colors. If we desire to marble books or papers we impregnate them with alum water, allow them to dry partly and take the edge from the size.
In the same moment that the paper soaked with alum comes in contact with the colors, the latter become bound by the formation of glycocholates of aluminium and do not run. They have the same property of fixing colors that resinous soaps used in the paper manufacture for gluing machine paper have. If this resinous soap were not too strongly basic, which is injurious to many colors, it might be applied as a surrogate for ox-gall.
As the resinous soap on account of its binding quality and insolubility could also be used in marbling with such colors, upon which it exercises no injurious effect, I will here give its preparation and former use in the manufacture of paper. If 2-5 ounces of rosin be boiled with 1-1/3 ounces of sodium lye and if you add by teaspoonful from time to time so much lye until a sample of it is dissolved by hot water to a clear fluid, the mass on cooling congeals and forms a quite solid soap. If we mix a solution of resinous soap with one of alum then we obtain an insoluble compound of resinous acids and aluminium. In this way resinous soap is used in gluing paper by adding to the paper pulp, first resinous soap and then a solution of alum. During this process a thin layer of insoluble soap of aluminium is formed around every particle of the paper and thus the running of the ink is prohibited. The same process occurs with ox-gall contained in the colors, when the edge is lifted off on paper or book-edges impregnated with alum, by which the running of the colors is prohibited.
The Preparation of Ox-Gall and Its Uses
The preparation of ox-gall to be used in marbling is simple. Take a quart of fresh bile (ox-gall or fish-gall), place in a bottle which contains when filled from 1-1/2 to 2 quarts, add 1/2 pint of absolute alcohol, shake well and leave stand for from 14 days to 3 weeks. Within this time all particles of gum and all fatty substances which are present in some galls in comparatively large quantities, will fall to the bottom and the gall will be thin-fluid, pure and diaphanous, brownish, yellow or greenish according to the nourishment of the animal from which it was taken.
Cow-gall contains more gum and fatty substances, than ox-gall; fish-gall, on the other hand, is thinner than ox-gall and would be the most useful of them all, if it could be obtained in sufficient quantities. If the gall is thin and pure it is filtered through paper which is easily and quickly done as it runs like water. If by filtering the dregs of the gall the filter should become clogged, a new one must be used.
The addition of alcohol causes the precipitation of glutinous and fatty substances and preserves the gall from decomposition. If prepared in such a way it can be preserved for years without spoiling.
All colors which we intend to use for marbling must be bound to bodies absolutely insoluble in water; it is therefore a mistake to say, that the colors dissolve in water. You may grind the color on a marble slab or in a machine as long as you please, but you will only obtain a great degree of fineness of the bodies but never a dissolution of the same.
Each body possesses its limit of divisibility; in amorphous bodies the high divisibility is but natural, but in crystalline bodies this division must be produced by grinding or washing.
The gall does not combine with these bodies, nor does it penetrate them, but only clings to them loosely. It can be readily removed in case the colors should be rendered useless by the addition of too much gall. The color is allowed to precipitate in the bottle and the water standing above is poured off, fresh water is added and this manipulation is repeated several times.
The gall which surrounds every particle of color forms, as it were, the support of it and adapts it to float upon the size.
Bodiless colors, which give a complete solution with water will run into each other on being thrown on the size and will flow from the paper when it is lifted off. The insolubility of the color bodies therefore prevents them from running although they are disarranged on the size in drawing and although one color may be compressed or expanded by a second, yet they all remain separate without mixing, except, perhaps, that the shade of the first color becomes more intense, because its color particles are pushed together by the more violent expansion of the second color.
From this it will be seen that the colors, to be useful for our purposes, must be thoroughly insoluble. The gall is added during the process of grinding the color, so that the particles of colors are fully surrounded by the gall. The gall has an excellent effect on the colors but it also can act very injuriously if the necessary precautions are not taken. Carelessness is mostly the reason that the edges do not possess the demanded lustre of color and why they appear pale, as the marbler often uses the gall too soon when he notices the smallest obstacle, (due in most cases to the size.) It is therefore not astonishing that brilliant comb or peacock-edges are so rarely seen.
It is an obstacle to marbling, that the gall mixes so easily with the size. It often happens that the gall spoils the size before an edge was ever produced on it. This happens especially when the size on which the colors are prepared according to the old method, is too thick. The size is frequently soiled and spoiled when the colors are prepared, because the colors can not be perfectly drawn off on thick size. There will always remain some particles which will not only soil the size but impregnate it with gall, and which will cause the entire uselessness of size and color.
A very consistent size will make the preparation of colors extremely difficult, as they need a double quantity of gall for the purpose of spreading out. If there is but one color used, the preparation on such a size would be possible without spoiling it, but with four colors this is entirely impossible because the repeated drawing off of the colors, which always leaves particles behind, will, by and by, impregnate the size so that when the fourth color is prepared the first will not spread out any further.
The more the impregnation of the gall and size increases, the power of expansion of the colors decreases and this continues until both materials are useless.
It is therefore advisable, as I have already stated, in the chapter upon the varieties of sizes that the colors should be prepared separately on a small part of size to determine the correct consistency of the latter and to prohibit the whole size being soiled.
The gall should be kept in a small bottle containing about 1/10 quart with a perforated stopper from which a small tube protrudes and from which the gall can be added to the colors in drops.
Although the preparation of the color in this way takes more time, this trouble is amply repaid by the result.
Fatty bodies are injurious to the size, therefore they must be carefully avoided because they have the same effect as the gall, they form, although not insoluble in water, a combination with the size and prohibit the colors from spreading out. Fatty bodies can be transferred by glutinous fluids into a state of the most minute division and they then form emulsions.
Natural emulsions are milk, the yolk of egg, and the milky saps of plants. For this reason, in many establishments raw milk is used as a propelling medium for hair-veined edges.
There are also fatty bodies which, in an artificial way, form an emulsion even with water; for instance, almond, poppy and hemp, if they are ground to a pulp with a little water yield a milky mixture. All these emulsions artificial as well as natural, can be employed as expanding mediums and give better results for marbling than petroleum or naptha.