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742 of very little worth. But by a series of new treaties, to which practically every State in central and south-eastern Europe has given its consent, the protection of these minorities is now placed under the authority of the League. When it is remem- bered how very mixed are the populations of the new States created by the Treaties of Peace, and how strong are the national feelings left by the war, it cannot be doubted that, if the League succeeds in securing the effective protection of minorities, it will do much to remove a very potent cause of trouble.

With regard to the League's work for disarmament, in addi- tion to the Permanent Commission to which reference has already n made, the Assembly recommended to the Council that it should adopt again the plan to which it had had resort in con- nexion with the project for the Court of International Justice; and accordingly the Council appointed a Temporary Mixed Commission, consisting of military men, of politicians, of econo- mists, of employers and of workmen, to study in more detail the application of Article 8, and to propose plans for the adoption of the. Council and of the Assembly. This Commission had only just begun its work in the summer of 1921.

As a result, then, of the general review which has been given of the Covenant in action, it may fairly be held that in technical spheres the results which the League had achieved up to the middle of 1921 had been good. In political matters they had, whenever the Covenant had been acted upon, been no less good. But only too often the Governments of the members of the League and the members of the Council had failed to apply the provisions of the Covenant to matters of political importance with which it was intended that the League should deal. Until the members of the League use the methods of the Covenant for dealing with all international questions of first-rate political importance which arise, the League cannot have that full author- ity by means of which alone it will be able at times of crisis to prevent the outbreak of great world wars. If the members of the League do use the methods of the Covenant, experience justifies the belief that they will secure the effective settlement of their disputes, and that in doing so they will calm the passions and mitigate the hatreds which otherwise are calculated so gravely to menace the peace of the world.

See also the articles INTERNATIONAL LABOUR ORGANIZATION and MEDICINE, INTERNATIONAL. (R. C.) LEATHER (sec 16.330). The decade 1910-20 saw considerable advances made in many of the processes incidental to leather manufacture. In addition to improvements in the older-fashioned methods of tanning, and the manufacture of leather generally, several new processes were perfected. The application of chemical control ih the leather industry during this period made great headway. Whereas previously most leather manufacturers worked on empirical methods, it is now the general rule for all large leather works to employ the services of a chemist; and in consequence methods of leather manufacture have become more scientifically exact than was previously the case. Changes of procedure made necessary by the cutting-off of certain supplies during the World War period have ultimately had a beneficial influence on the industry. Alterations in the manufacturing process, thus rendered com- pulsory, have resulted in the perfecting of more economical working of various processes, and many of the methods used have consequently been retained with advantageous results.

Tanning Materials. Additions to the earlier list of materials (see 16.332) are mimosa bark and mimosa extract. These tanning materials have attained a considerable degree of importance in the tanning of light and heavy leathers. Whereas mimosa was originally cultivated in Australia, it has latterly been introduced into S. Africa, which is now the principal source of supply. Acacia pycnantha (golden wattle) contains upwards of 4O%-45% tannin. Acacia decurrens (green or black wattle) contains 36%4O% tannin. This latter variety is the one which is now most commonly cultivated in Natal and Cape Colony ; its cultivation is also being carried out in northern Africa, Ceylon, and elsewhere. The manufacture of mimosa extract in S. Africa has become a commercial industry of considerable and increasing importance. This extract, which is exported from Natal in the solid form, contains from 6o%-62% tannin matter. The product possesses excellent tanning properties, producing a leather of a slightly pinkish colour; it is a fermentable

tannin which gives fair weight and rapid penetration, and is likely to compete with quebracho extract produced in Argentina.

Synthetic Tannins. Great advances have been made in the manufacture of synthetic tannins. The original product of this important branch of tanning agents was " Neradol," prepared by the action of formaldehyde upon phenolic bodies, under suitable conditions. Since the introduction of this product, patented by E. Stiasny and manufactured by the Badische Anilin und Soda Fabrik in 1911, considerable progress has been made in the production of tanning agents of this character. Products of this class made by British firms are commercially obtainable under the names of " Syn- thetic tannin," " Syntan," " Cresyntan," " Paradol," " Maxyntan."

The leather produced by synthetic tannin is of a white colour and possesses light-weighing properties. Its principal use is in conjunc- tion with natural tannins, either employing the material as a prelim- inary tannage prior to the application of the natural tannin, or using same in combination with the natural stuffs. Synthetic tan- nins differ from most natural tannin materials chiefly in the direc- tion that they permeate the pelt with great rapidity and thereby accelerate the tanning process. These products are very useful for employment by curriers and leather dressers in the retanning of leather which has only been lightly or half tanned, e.g. E. India tanned kips, goat and sheep skins. The rapid penetration of the tannin above referred to enables the retanning to be done in a minimum of time. Whilst, in the early stages of its introduction, many difficulties were encountered in the method of application of these products, improved processes used in their manufacture have eliminated most of these, and the results are quite reliable, and syn- thetic tannins are now somewhat extensively used.

The introduction of synthetic tannins undoubtedly marks an epoch in the history of leather manufacture. Whilst the progress made up to the present is not sufficient to allow of their entire sub- stitution for the natural products, it would appear probable that, aided by the great advances made in chemical technology, the day may not be so far distant when leather will be produced entirely by products of this kind.

Sulphite Cellulose Extract. This product, sold under the names of " Wood Pulp Extract," " Spruce Extract," etc., results as a by- product from the manufacture of paper from wood pulp. The liquor resulting on the treatment of wood with calcium and sodium bisulphite in the manufacture of cellulose was, prior to about ten years ago, a waste product which had no industrial application. By a special method of treatment, with a view to ridding the product of objectionable impurities, e.g. calcium and iron salts, and subsequent concentration, an extract was prepared of i8-25 Baum6, which has considerable application in the manufacture of leather. Whilst the product may not be regarded as a true tanning agent, it may be employed in conjunction with natural tannins. The material is most generally applied towards the latter end of the tanning process; and when retanning leather for the purpose of obtaining increased weight, the application is made when the tanning process is almost entirely complete. The fact that this is a by-product and can, consequently, be cheaply prepared, has caused it to be used to quite a considerable extent. The amount of matter absorbable by hide powder present in the commercial products varies from about 18 % to as high in some cases as 25 %.

Analysis of Tanning Materials. The method of analysis most generally used is the hide-powder method, resulting upon the work of the International Association of Leather Trades' Chemists and the Society of Leather Trades' Chemists. This method for the estimation of tannin, whilst still being somewhat empirical, en- ables the obtainment of concordant results, and furnishes a figure which bears some relationship to that obtainable in practical tanning.

The following is the method of carrying out the analysis which is officially recognized by the Society of Leather Trades' Chemists : Such a quantity of material shall be employed as to give a solution containing as nearly as possible four grams of tanning matter per litre, and not less than 3-5 or more than 4^5 grams. Liquid extracts shall be weighed in a basin or beaker and washed with boiling dis- tilled water into a litre flask, filled up to the mark with boiling water, and well mixed and rapidly cooled to a temperature of 17-5 C., after which it shall be accurately made up to the mark, again well mixed, and filtration at once proceeded with. Sumach and myr- abolam extracts should be dissolved at a lower temperature. Solid extracts shall be dissolved by stirring in a beaker with successive quantities of boiling water, the dissolved portions being poured into a litre flask, and the undissolved being allowed to settle and treated with further portions of boiling water. After the whole of the soluble matter is dissolved, the solution is treated similarly to that of a liquid extract. Solid tanning materials, previously ground till they will pass through a sieve of five wires per centimetre, are ex- tracted in Koch's or Procter's extractor with 500 c.c. of water at a temperature not exceeding 50 C., and the extraction continued with boiling water till the filtrate amounts to one litre. It is desirable to allow the material to soak for some hours before commencing the percolation, which should occupy not less than three hours, so as to extract the maximum of tannin. Any remaining solubles in the material must be neglected, or reported separately as " difficultly soluble " substances. The volume of liquor in the flask must, after cooling, be accurately made up to one litre.