364 



THE INDIA RUBBER WORLD 



[July 1, 1911. 



The Valuation of Crude Rubber. 



THE following propositions relating to the uniform execu- 

 tion of comparative preliminary work in the determina- 

 tion of the value of crude rubber were prepared by Dr. 

 Fritz Frank, Berlin, for tlie German section of the International 

 Rubber Testing Committee. 



A. Gener.\l Report. 



At the first session of the German section of the "International 

 Rubber Testing Committee" in Berlin, Professor Dr. Warburg, 

 Berlin, secretary of the German section, and the president. Dr. 

 Berkhout, presented a most important question, the provision of 

 standards for the valuation of raw rubber materials. 



Dr. Frank, Berlin, reported on experiments in this direction. 

 He proposed to follow the suggestions made independently of 

 each other and according to different methods, by members of 

 the commission, including Dr. Axelrod — whose death had oc- 

 curred in the meantime — and later by Dr. Schidrowitz, London, 

 by the comparative measurement of the viscosity of rubber solu- 

 tions. After Dr. Kuhlmann, Harburg and Dr. Thiel, Obcr- 

 Schonweide, as rubber manufacturers had described their own 

 satisfactory experience in the valuation of rav/ rubber by com- 

 parative measurement of the viscosity of similar solutions pre- 

 pared from it, Dr. Frank was commissioned to work up this 

 apparently practicable method of working in such manner as 

 to make it possible for him to submit it, in the form of a 

 proposition to the committee as a whole and to make it gen- 

 erally known, so that, by as numerous a body as possible, ex- 

 periments could be conducted at different points and in this 

 manner unobjectionable matter could be obtained, from which 

 it might be learned whether this method of working is adapted 

 for an international system of testing crude rubber. 



By written communication with all the members of the Ger- 

 man section of the committee, in the further development of 

 initial steps, the details of the proposition, in regard to a gen- 

 erally comparable working system, were perfected. 



Before undertaking in the course of his paper to report on 

 the propositions and the carrying out in detail of the working 

 plan, the author emphatically stated that the members of the 

 commission do not question that the proposed method is still 

 in the early stages of its development. It is intended to be 

 only a proposition, the general or special usefulness or non- 

 utility of which remains to be determined by the comparative 

 combined work of the colleagues interested. Inasmuch as the 

 comparative working results demand the employment of corre- 

 sponding, or at least similar processes, it is proposed to describe 

 them as they are here employed and as they have already found 

 further introduction, on the basis of these propositions. 



The theoretical speculative foundation for the hitherto un- 

 proved applicability of the viscosity calculation of rubber solu- 

 tions, in estimating the value of rubber, lies in the empirical 

 experience that solid, good rubber varieties furnish more viscous 

 solutions than such as are soft and of low grade value. On 

 this experience the acceptance of the applicability of calcula- 

 tions of this nature, in the valuation of crude rubber, has been 

 based. As already stated, in Dr. Axelrod, the deceased member 

 of the commission, it found a special advocate, and in the works 

 of the English member. Dr. Schidrowitz, it has found further 

 support. Numerous comparative operations, conducted here, 

 have, moreover, furnished a certain support for the general 

 dissemination of the proposition. In regard to the experiments 

 made here, it seems fitting to state that it is not the comparison 

 of the positive viscosity figures that appears to constitute an 

 actual value standard, but that only the comparison of figures, 

 with regard to the various kinds, or according to their place of 



origin, will be practicable. As comprehensive a co-operation of 

 all circles as possible is desired. It is not intended, however, 

 that the propositions made known herewith shall in any respect 

 limit the efforts and experiments that may be made to solve 

 the problem by other methods. The programme of the com- 

 parable and more general work according to the proposed plan 

 of working is briefly set forth as follows: 



1. Comparative determinations of the viscosity of rubber 

 solutions in uniformly prescribed apparatus according to uni- 

 formly determined methods of definite intervals. 



2. Comparison of the viscosity values determined, with the 

 chemical-physical investigation results obtained with vulcanized 

 crude rubbers, subjected to the same preliminary treatment and 

 prepared in the same manner. 



B. Special Retort on the App.nratus and Working Methods 

 IN Detail. 

 I. The Appar.^tus for Determining Viscosity. 

 The apparatus proposed for general use (*) after having 

 undergone various modifications, 

 consists of the following parts. (Fig. 

 1.) The receiver a, is a pear-shaped 

 glass vessel, which is equipped on 

 the side with the inflow socket b, 

 provided with a ground in stopper, 

 and at c with a similar socket, which 

 carries the closing rod d. The ves- 

 sel shows three marks for the meas- 

 urement of 200 cc. m. The three 

 marks serve for measuring in and at 

 the same time for the establishment 

 of a certain level. At the low-er end, 

 at e, the vessel has a discharge pipe 

 of metal of a predetermined length, 

 which is firmly set in a glass socket. 

 The closing rod d is ground to close 

 this outlet perfectly. The aluminum 

 closing rod is, moreover, carried by 

 the double guides in the holder /. 

 By means of the ground collar g, 

 the glass vessel a is attached to the 

 receiving cylinder h. Both grindings 

 have in i connecting openings to al- 

 low the air to escape, or by slightly 

 turning the vessel h they may be 

 closed. The receiving cylinder It is 

 graduated, and from the 95 cc. m. 

 to the 105 cc. m. mark is contracted 



to permit of accurate reading. The cylinder is mounted on a 

 broad wooden foot. The dimensions are invariable. The ap- 

 paratus is constructed, under my directions, by a Berlin firm.** 



II. Conducting the Crude Rubber Test. 

 A properly taken average sample of crude rubber of 250 to 



*In the construction of the apparatus, I have followed the suggestions of 

 Axelrod. Gummi-Zeitung, 1905, page 1054. In exhaustive tests, in new 

 construction, great difficulty was experienced owing to its Ijeing almost 

 impossible to make the outflow pipe, of 7 m. m. clear width, absolutely- 

 uniform and to grind or melt oil the end absolutely level. Further diffi- 

 culty was experienced in the lead and boring of the cock: finally the width 

 of the _ receiving cylinder prevented exact reading. .Ml these separate 

 difficulties resulted in such inaccuracies in the apparatus constructed, that 

 one after another, the above-named sources of error hari to be eliminated. 



**German Registered Design of the firm of Paul .Mtniann, Berlin. Louisa 

 street. No. 47. The apparatus, under exact enumeration, is tested by the 

 Chemical Laboratory for Commerce and Industry of l)r. Henriques, suc- 

 cessor. The second illustration shows a complicated apparatus consisting 

 of the parts of the viscosimeter with two closing rods, thermometer, filling 

 funnel, seconds clock and a bottle of glycerine of 1.25 spec, grav., for 

 testing the apparatus. 



