Gum tragacanth, also called gum-dragon, is the product of various species of astragalus which is found in Greece and Turkey and is a natural exudation of shrubs and from exudations resulting from incisions made in the stem near the root. This shrub is from 28 to 35 inches high and two inches in diameter. It is collected in July and August after the exudations have ceased. It is a hard, tough substance more or less white according to its purity in very irregular flattened shapes and in tortuous vermicular filaments. It contains aside from a little gum and starch, a consistent plant-mucilage without smell or taste and it is used in technical ways, in printing of textile fabrics and finishing, in producing plastic masses, as a binding medium for the production of confections and in the book-bindery for marbling size.

The leaf tragacanth of Smyrna is the best. It is brought to the markets of the world via Constantinople or via Smyrna in boxes of 100 to 200 lbs.

It forms flat ribbon-like pieces which consist of peculiar layers of horn-like consistency, white and diaphanous; when broken it is dull and splintered.

An inferior quality is the tragacanth of Morea, which generally comes from Greece via Trieste. This consists of oddly shaped, peculiarly twisted pieces, partly of pure white, partly of yellowish and brownish colors. For a long while, tragacanth was known as a good material for marbling size and, for that reason, it is used to-day in a good many of our book-binderies for this purpose.

It is much more liked than carrageen moss because the consistency of its mucilage and its durability are great and the preparation of the colors does not demand such great attention. But since my experiments and investigations upon the excellent effects of borax on the durability of carrageen size have become known, tragacanth has lost much of its popularity, because with it the edges can never be produced in a similar fine way as with carrageen size and besides the price is higher. Tragacanth is one of these short-viscous plant mucilages which swell in cold water but do not give a perfectly homogeneous solution. The mucilage consists of innumerable small granules, in which the starch is enclosed by cells.

These small granules prohibit, within the first two or three days of a fresh tragacanth size, the drawing of edges, as they make the colors thrown on appear rugged, and in drawing injure the fine hair lines. Five or six days after the dissolving of the tragacanth, the mucilage becomes more homogeneous and therefore better adapted for marbling.

If the swelled up mucilage is boiled, after the first or second day, then the solution will become perfectly homogeneous and will be as good as carrageen size except that the colors, which normally spread out on carrageen size, will expand much more on tragacanth size as it possesses more consistency and therefore they will become paler. The more dense the size, the thicker colors and the less gall is necessary to produce a normal expansion. The same difference in the power of expansion of the colors as in carrageen and the tragacanth is noticed in colors which normally spread out on tragacanth but which, very largely, expand on the size of plantago-psyllium (flea-bane) because the latter has the most consistency and homogeneity of them all. The different effects of the varieties of size on the colors are due to the consistency and to the different conditions of gravity. The objections of the consumers of my marbling colors who use tragacanth, are, that they consider the edges too pale. The cause of this is that my products are only prepared for carrageen size, inasmuch as my investigations have shown that it is the best, the cheapest and the most adapted for all varieties of edges.

The homogeneousness of the tragacanth mucilage in cold solution comes naturally after the size is five or six days old, because within this time fermentation of lactic acid occurs, which opens the cells of the small granules of starch while at the same time boiling heat has an immediate result in the same direction.

As soon as these cells are opened the formation of acids of the sugary parts and the fermentation of lactic acid of the starch contained in the size take place as fast as in any other variety of size, hence the size of tragacanth has no superiority over any other, besides the best, or picked-leaf tragacanth of Smyrna costs about four times the price of the best Carrageen.

For the preparation of the size, take 3 ounces of tragacanth, pour two quarts of water over it, leave it stand for 24 hours, then stir well and leave it standing for 12 hours more, repeat this until the homogeneous thick mucilage has been produced, then add 4 quarts of water, again stir it up well and filter it and the size is ready for the marbling process.

For tragacanth size, colors of great consistency, mostly fine earth colors are the best. They must be ground exceedingly well and very little ox-gall is to be added. But as these earth colors lack in the power to spread out and in divisibility, a characteristic of colors prepared for carrageen size, and as they never will have such fineness and smoothness, always appearing rugged, it is impossible for me to recommend gum tragacanth for the preparation of size.

I must mention further an effect, which earth colors exert on tragacanth size, viz., that they can be used on paper not prepared with alum, without running, while this is not the case with colors, which were prepared for the Carrageen size. In another chapter upon ox-gall I shall explain why the colors used with Carrageen size must be transferred on alum paper.