July 1, 1911. 



THE INDIA RUBBER WORLD 



365 



300 g. weight is first of all, for the preliminary work done in 

 factories and laboratories, cut up, softened for 30 minutes in 

 hot water, rapidly washed in the washing rollers by a competent 

 operator, and then dried in the air, in a place protected from 

 light, without artificial heat. All stretching during the washing 

 process and all kneading and heating must absolutely be avoided, 

 but the sample must be washed to a film as thin as paper, which 

 facilitates rapid drying and solution. Treatment in the rollers 

 must not last longer than 20 minutes. 



Departures from the method of washing must be absolutely 

 avoided ; where this is impossible with differing methods, the 

 departures must be accurately recorded in detail, in the report 

 of the results of the experiment. Generally speaking stress must 

 be laid on the necessity for the most careful recording of the 

 various observations, so that differences may be explained. 



It is reserxed for later experiments so to simplify the washing 

 that material that has not been rollered can be used for vis- 

 cosity determinations, in order that planters and dealers, who 

 have no washing apparatus, may be enabled themselves to con- 

 trol their crop as a commercial product. 



Fig. II. 



III. The Solvent. 



As a solvent commercial xylole is recommended, because it 

 has a relatively high flashing point of only 21° C, and conse- 

 quently does not evaporate so rapidly, moreover, it can be 

 obtained everywhere uniformly at a comparatively reasonable 

 price and of good purity. This solvent is required to show: 

 Specific gravity, at 15° C, 0.867-0.869. Boiling point : accord- 

 ing to commercial practice and the processes described in all 

 technical analysis books, should range between 135 and 140° C, 

 90 per cent, distilled off. 



IV. The Dissolving Vessel for the Rubber. 

 (a) A small glass vessel of about 1 liter capacity of dark 

 glass, with a screw-threaded metal cover, through which a 

 stirring apparatus operates, such as is frequently used in the 

 household, may be used. 



The stirring apparatus should consist of simple, strongly 

 connected, dry and hard wooden strips, or they may be of por- 

 celain or glass, which are easy to clean. This dissolving vessel 

 should always be tared and the tare etched on it. 



(b) A liter bottle, of brown glass, with ground in glass 

 stopper and the tare etched on it. 



V. The Solution of the S.\mple. 

 The solutions for testing should be exactly 3 per cent. 



(a) Nine to 15 grammes of the dried rubber sample is weighed 

 out, cut up, and for the first steeping covered with about 100 cubic 

 centimeters of xylole poured over it and allowed to stand until 

 as uniform a solution as possible is effected. Then it is stirred 

 and gradually, according to the nature of the rubber, the solution 

 is made up and completed. The quantity of solution weighed in 

 must be at least 300 to 500 grammes. The gross weight of the 

 dissolving vessel, with the solution must be determined on each 

 occasion before the commencement of the determination of vis- 

 cosity, so that possible losses of solvent in the finished solution 

 may be replaced and uniformly mixed in again. 



(b) The dry rubber is weighed out, then placed at first in 

 a small quantity of xylole and left to steep a short time, for 

 a first steeping. Then gradually, as needed, the remainder of 

 the xylole is added, the vessel closed and the final solution so 

 assisted by occasional vigorous shaking up that it is finally 

 completed in 30 hours. 



VI. Conducting the Determin.'^tion of Viscosity. 

 The glass retort a, Fig. 1, the discharge opening being closed, 

 is filled with the solution e-xactly to the 200 cc. m. mark. For 

 the measuring temperature, 20° C. is always employed. In the 

 older apparatus, the cock was turned from stop to stop; in the 

 newer testing apparatus, the closing rod d is raised by a quick, 

 but always steady movement to the stop and at the same time 

 the stop-pin of the stop watch (seconds watch) is pressed open. 

 As soon as the fluid has run as far as the lOO mark down into 

 the lower vessel, the closing rod and stop watch are simultan- 

 eously set and the elapsed seconds read off. As so far no unit 

 has been established, it is possible only to give the time required 

 for 100 cubic centimeters of the above described preparation to 

 run out.f The second determination of viscosity is carried out 

 after 8 or 10 days with the remainder of the solution, wdiich 

 must be kept in a dark place.tt 



VII. Cle.\ning the Vessels. 

 -Mter running and pouring off the rubber solutions, the ves- 

 sels are cleaned exclusively by pouring alcohol into them. The 

 rubber is precipitated as a homogeneous mass and can either 

 be washed out in a whole piece, by means of the alcohol, or 

 removed mechanically. The discharge-tubes are freed, by 

 means of a feather brush, from adhering rubber particles. 

 Acids or alkalies should never be used. Before undertaking a 

 new experiment, the alcohol must always be completely evapo- 

 rated and the vessel absolutely dry. 



VIII. Compar.\tive Vulcaniz.\tiox Experiments. 

 The residue of the dried rubber film that has not been used to 

 make solution is mixed with 8 to 10 per cent, of sulphur, with 

 no other addition, in the customary manner and pressed or 



tjt appears to me advisable to use, to commence with, a glycerine of 

 1.25 (30 degs. Be.) as the unit fivid, because this can be obtained every- 

 where of uniformly equal purity. It would thereby become possible, as in 

 oil viscosimeters, to establish really uniform normal values even in the 

 case of minor and unavoidable constructive errors in the apparatus. 

 Furthermore, I would recommend, in order to reduce the working errors 

 as far as possible, to allow not 100 cubic centimeters, but 200 cubic centi- 

 meters of the rubber solution to run out. 



ttThe behavior of the solutions, when standing, appears to be character- 

 istic of the conservation of raw rubber. In connection with Dr. Marck- 

 wald, I observed that a rapid thinning or a turbidity, or the formation of 

 a solid precipitate, in certain kinds, was an indication of typically low 

 grade varieties. On the other hand, sustained viscosity and the permanent, 

 uniform suspension of non-rubber substances, in the light and in the dark, 

 were characteristics displayed only by rubber varieties which proved good 

 in the course of manufacture and in storage. Concerning this line of 

 experiments there will be more said later. 



