104 



THE INDIA RUBBER WORLD 



November 1, 1920 



and (3) by the temperature. Doctor Stevens does not at this 

 stage put forward a theory to account for the preservative action 

 of the water vapor, as further experiments to this end are in 

 progrress. 



CONCLUSIONS 



1. The hfe of vulcanized rubber is prolonged by storing in 

 air saturated with moisture or petroleum vapor. Even over- 

 cured rubber can be preserved by this means for si.x or seven 

 months al tropical temperatures. 



2. Preserved under these conditions, the acetone extract does 

 not increase, showing that the rubber is protected from oxida- 

 tion and decomposition. Nevertheless, the physical changes char- 

 acteristic of "after-vulcanization" proceed normally. 



3. In dry air the chemical change (oxidation) takes place 

 more rapidly than in air containing moisture, and an increase 

 in the acetone extract takes place. 



4. As the oxidation of soft vulcanized rubber lakes place the 

 more rapidly the higher the coefficient, and is accompanied by 

 an increase in the coefficient, and as vulcanized rubber, when 

 perished, tends to become soluble in acetone, the percentage of 

 combined sulphur or coefficient in such case should be based 

 on the weight of the specimen after acetone extraction. 



VISCOSITY OF RUBBER SOLUTIONSi 



In investigating the viscosity of rubber solutions, the following 

 method was used by the Delft rubber laboratories : 



.^bout one gram of the finely cut up rubber sample is placed 

 in a hollow flask and shaken on the machine with 100 cc. chem- 

 ically pure benzol, boiling point 80 degrees C, until the rubber is 

 about 80 per cent dissolved. The solution is filtered through 

 glass wool and the viscosity measured in Ostwald's viscosimeter, 

 of the Fol type, at constant temperature, in diffused light. The 

 first number is taken as the basis. The test is repeated in order 

 to guard against errors. This always shows low values. The 

 time taken to flow out divided by the time taken to flow out of 

 pure benzol gives the relative viscosity. The concentration was 

 determined by evaporating 25 cc. of the solution. 



factohs influencing results 



Inkluence of the Light and of the Discharge Through a 

 Capillary on the \'iscosity of Rubber Solutions. It is recom- 

 mended that the work be carried out in a subdued light and to 

 use the first observation of the viscosity. 



Influence of Moisture and of Acid on the Viscosity of 

 Rubber Solutions. While water appears to play no great part 

 in the determination, acid, even in traces, must be kept out for 

 a correct determination. 



Influence of Incomplete Solution on the Viscosity of 

 Rubber Solutions. The resins are more easily soluble than the 

 rubber, therefore if the solution is not complete enough low 

 viscosity numbers will be obtained, while if agitation is carried 

 too far the nitrogen compounds dissolve and the viscosity is 

 raised. In all ca.scs the greatest part of the rubber must be 

 dissolved, otherwise the viscosity numbers must be taken with 

 reservation. 



Influence of the Nature of the Solvent on the Viscosity 

 or Rubber Solutions. It was found that the quotient of the 

 relative viscosity of various rubbers for two different solvents 

 is not constant, that it is proportionately greater with rubbers 

 having high viscosities than with those of less viscosity. It is 

 therefore important that the same solvent should be used if a 

 comparison is to be made. 



Influence of the Resinous Bodies on the Viscosity of 

 Rubber Solutions. Extracted rubber shows a less viscosity 

 than crude rubber. This is not a fact which applies to all 

 cases. The separation of the resin causes this diminution of 



the viscosity or it may be the extraction treatment. In any 

 case it is not possible from a solution of the resins on the one 

 hand and the extracted rubber on the other by mixing these 

 to form a mixture in which the original viscosity is raised. 



Influence of Sulphur and Compounds on the Viscosity of 

 Rubber Solutions. The simple mixing of sulphur and com- 

 pounding materials does not change the viscosity. In the cal- 

 culation it is only necessary to bear in mind the change of the 

 concentration due to the compounding ingredients. 



The Importance of the Viscosity Determination. There 

 exists an actual relationship between the viscosity and the tensile 

 strength. The viscosity also shows the important factors con- 

 cerning the quality of the rubber. 



The Measurement of the Swelling Power of the Rubber 

 Gives VALitABLE Conclusions Concerning the Quality of the 

 Rubber. However, as yet, not enough work has been done on 

 this property to give definite results. The swelling power is 

 proportional to the viscosity. 



LABORATORY APPARATUS. 



FLASK SHAKING DEVICE 



A patented device for securely clamping and shaking a half 

 dozen flasks at one time is shown in the illustration. The 

 size of the flasks held may vary from si.x to 24 ounces capacity. 

 The use of this machine great- 

 ly facilitates the operations of 

 solution or precipitation where 

 much routine work of such char- 

 acter is involved. 



The power required for oper- 

 ation of the apparatus is about 

 one-sixth horse-power. The ma- 

 chine is arranged for attaching 

 to a bench by screws and is con- 

 nected by a round leather belt 

 to a motor. — Eimer & Amend, 

 211 Third avenue. New York 

 City. 



Clamp Shaking Machine 



IMMERSION HEATER FOR LABORATORY 



The new immersion type water heater shown herewith, con- 

 sists of nickel-chromium heating elements incased in a flat brass 

 casting which protects them from mechanical injury, and making 



a simple and durable heater that 

 is easily cleaned. When pro- 

 tected in this manner the life of 

 tlie heating elements is in- 

 creased, requiring less frequent 

 renewals than with the ordinary 

 immersion type heater. 



This heater is particularly use- 

 ful in the chemical laboratory 

 for heating or evaporating wa- 

 ter in any shallow container, and 

 may also be used with glue pots, 

 paste kettles, sterilizers and 

 other apparatus. 



Electric Water Heater 



' Communications of tlic Nethcrland Government Institute for Advising 

 the Rubber Trade and the Rubber Industry, Delft, Holland. 



To install the heater, a IJ^-inch hole is drilled through the bot- 

 tom of the container and the heater inserted from the top, so 

 the extension through which the Cord is run projects downward 

 through the hole. Tightening the nuts and washers holds the 

 heater rigid and prevents leakage. 



By means of a snap switch on the heater cord three different 

 heats may be obtained: 1,200 watts, 600 watts and 30O watts. 

 Standard heaters are made for 110, 120, and 220 volts, and may 



