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