170 



THE INDIA RUBBER WORLD 



Decemher 1, 1920 



viscometer. The tank is also fitted with a movable wooden lid. 

 while an electric lamp placed at the back insures sufficient 

 illumination. 



So far, viscometers of the Ostwald type have been employed, 

 the bore of the capillary being chosen to suit the thickness of 

 the particular solution in use. The viscometers are supported 

 in the water in a vertical position in a wooden stand designed 

 for the purpose. 



It has been found tliat the temperature of this thermostat 

 can be icgulated to within one-tenth of a degree without anv 

 difficulty, and can be maintained constant for long periods. 

 UNITS OF MEASUREMENT 



Instead ut comparing the viscosity of the rubber solutions 

 with some arbitrary liquid such as glycerine or with the pure 

 solvent itself, as has been previously done by all investigators 

 of the subject, the measurements have been calculated to an 

 absolute value. In the .Report of the Chemical Society, of Lon- 

 don, on the Progress of Chemistry it is strongly advised that in 

 future all viscosity measurements should be expressed in abso- 

 lute values. In this way numbers can be obtained which will 

 be entirely independent of the type of apparatus used and of 

 the conditions cf tlie experiment and which can be repeated by 

 others. 



For purposes of calculation the viscosity of a liquid may be 

 defined as the force which will move a unit area of plane sur- 

 face with unit speed relative to another parallel plane surface, 

 from which it is separated by a layer of the liquid of unit thick- 

 ness. This force, measured in dynes per square centimeter, is 

 called a "poise" and a hundredth part of this rnit is termed 

 a "centipoise." The centipoise has been adopted as the unit 

 for all the viscosity measurements described below. 



In the Bulletin of the American Bureau of Standards for 

 1917, tables are published giving the viscosity of solutions of 

 pure sucrose (cane sugar) and of mixtures of ethyl alcohol 

 and water, expressed in centipoises, for different concentrations 

 and temperatures. These values have been made use of in 

 standardizing the viscometers employed. 

 EXPERIMENTAL 

 The first series of measurements described in this paper Heals 

 with the viscosity of different kinds of plantation rubber dis- 

 solved in chloroform. The solutions all have a concentration 

 of 1 per cent and are made up by shaking the weighed amount 

 of finely divided rubber with known volume of pure chloroform 

 in a power-driven shaking machine. 



In Table I are to be found the chemical constants which were 

 first of all determined for the rubber samples. 



T.SBLE I 



P.vLE AND Light Amber Crepes from IJhterent K.st.\te.s. First Grade 



Rubbers from First Latex. 



Caoutchouc hy 

 OilTerence, 



Including Mineral 



Serial No. Vrotcids Resin Moisture Mattt-r 



for Reference Per Cent Per Cent Per Cent Per Cent 



1 96.93 2,62 0.28 0.17 



2 96.77 2.65 0.30 0.28 



3 97.01 2.40 0.30 0.29 



4 97.1.'! 2.38 0.22 0.2.^; 



S 97.13 2.30 0.30 0.27 



The viscosity values were as follows : 



Viscosity at 25 Degrees C. 

 Serial No. in Centipoises 



4 .: 41.6 



3 37.5 



1 34.6 



5 27.3 



2 ;.. 22.5 



Examination of these values will show that, generally speak- 

 ing, a high viscosity is associated with a low resin and high 

 caoutchouc content, while a low viscosity corresponds to a high 

 percentage of resin and a lower caoutchouc content. 



In Table 11 are drawn up the results obtained on a number of 

 high grade smoked plantation sheets from different estates. 



Table II 

 Caoutchouc by 

 Difference. 



Including Mineral 



Serial Xo. Proteids Resin Moisture Mailer 



f(.r Reference Per Cent Per Cent Per Cent Per Cent 



8 96.81 2.61 0.34 0.24 



9 95.81 3.38 0.47 0.34 



10 96.27 3.05 0.40 0.28 



11 96.29 2.92 0.58 0.21 



12 96.75 2.52 0.48 0.25 



13 96.15 2.89 0.50 0.40 



14 95.95 3.23 0.42 0.40 



15 95.87 3.25 0.60 0.28 



16 96.41 2.56 0.64 0.36 



17 96.87 2.47 0.48 0.18 



IS 96.84 2 60 0.40 0.16 



19 96.67 2.50 0.34 0.23 



Viscosity at 

 Serial .\'o 25 Degrees C. in Centipoisea 



15 26.6 



13 25.9 



17 25.2 



19 25.2 



18 23.9 



11 23.8 



It 23.8 



8 21.8 



12 21.8 



16 21.8 



10 19.1 



9 16.3 



Examination of these values will show, that with one or two 

 notable exceptions, including No. 15, there is again a tendency 

 for low resin content to correspond with high viscosity and 

 vice versa. Moreover, on the average the resin contents are 

 higher than those of the pale crepes and the viscosities corre- 

 spondingly lower. 



Samples Nos. 6 and 7 which are not included above were two 

 lower grade compound crepes and their viscosities were 17 and 

 19.8, respectively. 



A certain number of determinations w^ere carried out of the 

 tensile strengths of a trial compound made from different sam- 

 ples of rubber. The breaking strain of rings cut from the com- 

 pounds was measured on the Schopper machine and the result 

 calculated from the dimensions of the rings to pounds per square 

 inch. The results were as follows: 



Viscosity values were as follows : 



Tensile Strength 



Seri.-il Xo. in lbs. per sq. in. Viscosity 



13 1,923 25.9 



al 1,689 23.8 



12 1,662 21.8 



17 1,615 25.2 



16 1.502 21.8 



18 1,479 23.9 



15 1,343 26.6 



These preliminary e.xperiments support Schidrowitz's view 

 that the relation between viscosity and tensile strength of the 

 rubber is not direct. Further work on this point is required 

 and the writer hopes to undertake it shortly. 



The only conclusion which may be of some value which can 

 be drawn from these early experiments seem to be that the vis- 

 cosity of rubber solutions in cliloroform is modified in the case 

 of high grade plantation rubbi-rs by their resin content in the 

 way described above. 



RUBBER FILLER 



Ground tufa rock of specific gravity 2.25 is being advocated as 

 a filling ingredient for general rubber compounding. Its composi- 

 tion is given as chiefly silica and alumina with small percentages 

 of lime, magnesia, oxide of iron and compound of sodium and 

 potassium. It shows loss of 6.5 per cent on ignition. 



The Miller Rubber Co. has been highly complimenteu on 

 the striking window display which it is offering to dealers in its 

 products. It consists of reproductions in' eight colors of original 

 pantings by means of the Tullograph oil color reproduction 

 process, in w^hich no ink is used, but only oil and paint, so that 

 the colors will stand up under sun and rain and can be cleaned 

 with a damp cloth. This makes the display adaptable for out 

 of doors if desired. 



