496 



THE INDIA RUBBER WORLD 



April 1, 1921 



can lie worked satisfactorily with steam shovel, whereas most 

 Tennessee and practically all Missonri deposits are so small that 

 they are milted by pick and shovel. 



Barytes as received at the factory is crushed, mixed with coal 

 and burned at 1,200 to 1,300 degrees C. from two to three hours 

 in rotary kilns. The black ash formed is leached, giving a solution 

 of barium sulphide. 



ZINC SULPHATE SOLUTION 



In the manufacture of zinc sulpliatc any form of zinc or zinc 

 oxide such as skimmings, zinc ash from galvanizing kettles, im- 

 pure oxides or zinc carbonate ores may be dissolved in sulphuric 

 acid. Zinc sulphide or roasted zincblende may also be used. The 

 resulting solution is purified by various oxidizing processes, de- 

 pending on the nature of the liquor. 



LITHOPONE 



Bv mixing proper proportions of the zinc and barium li(|uors, 

 lithopone is precipitated. Plate and frame presses or continuous 

 lilters are used in filtering the pigment and the cake is dried and 

 healed in muffle furnaces to about 500 degrees C. When uniformly 

 heated the material is raked out, quenched in water and ground 

 to remove grit due to sand from the furnace walls or to the 

 sintering of overheated particles of lithopone. The ground pulp 

 is washed, filtered, dried, pulverized, sometimes air floated, and 

 packed in barrels of 400 pounds or bags of SO pounds. 



USES OF LITHOPONE 



Lithopone is surpassed in whiteness only by the finer grades of 

 zinc oxide. Large quantities of lithopone are used in the manufac- 

 ture of paint, rubber goods, linoleum, wall paper, window shades 

 and printing inks. The lithopone industry has grown from 920 

 tons in 1900 to a production of 79.619 tons in 1919, and it is 

 expected that the 100,000-ton mark will be reached in 1920 or 1921. 



THE ABSORPTION OF LIGHT BY CAOUTCHOUO 

 By S. Judd Lewis and B. D. Porritt' 



In view of the changes which are produced in rubber when 

 exposed to light and air, it is somewhat surprising that no record 

 appears to exist of any effort having been made to study the 

 action of light on caoutchouc in a quantitative manner. It 

 was therefore decided to carry out some preliminary experiments 

 to determine the character of the absorption of light of short- 

 wave length by caoutchouc, to which experience has shown that 

 the successive physical and chemical changes which occur during 

 "perishing" must be attributed. 



With this object a specially good sample of fine hard Para 

 rubber was selected in the crude condition before subjection to 

 any manufacturing operation. This was cut into fine strips and 

 sulimitted to repeated extraction with cold distilled water for a 

 period of over a week, followed by extraction with cold acetone 

 until the washings were no longer colored. A final prolonged 

 digestion with several changes of absolute alcohol was employed 

 to ensure the complete removal of resins and soluble coloring 

 matters, and the extracted rubber was thereafter dried at ordinary 

 temperature in a current of hydrogen to prevent oxidation. The 

 dry material was then transferred to a stoppered separating 

 funnel in which it was allowed to swell and slowly dissolve in 

 anhydrous ethyl ether (purified by treatment with sodium and 

 fractional distillation) without agitation. The clear caoutchouc 

 solution was withdrawn at intervals before it became unduly 

 viscous, from the bottom tap, the passage of proteid and insoluble 

 matter being prevented by the insertion of a small plug of asbestos 

 fiber, and the volume removed was replaced by the addition of 

 fresh solvent. 



In this way a sufficient quantity of a perfectly transparent, 

 colorless solution of caoutchouc was obtained containing approxi- 

 mately 0.94 ])cr cent of solute by weight. As it was found that 

 this solution gave only very feeble absorption, it was reduced 

 by spontaneous evaporation to about two-thirds of its original 



volume, thus increasing its strength to aiiproximatcly 1.5 per 

 cent. 



The method of procedure followed was similar to that described 

 elsewhere with the exception of the photometer emjiloyed, which 

 was of the new sector type, the details of which have lately been 

 published*. 



The 2-cm. cell containing the solution was placed in one path 

 of light, and a duplicate cell filled with the puriiicd ether, similar 

 to that u.sed for the preparation of the solution, was placed in the 

 other beam for the pur]>ose of providing a control. The absorp- 

 tion effect was therefore confined to the solute alone, that of the 

 solvent being eliminated. The ether employed was found to give 

 no absorption at wave lengths above 2170 sufticient to interfere 

 with the experiment. 



The results obtained are exhibited in the accompanying curve, 

 m which are plotted the values of the extinction coefficient, that 

 is of log 1/r, relative to a three per cent solution in a cell of 

 vinit thickness as ordinates against wave lengths as absciss:e (I is 

 the intensity of the incidental light, and I' is that of the light 

 transmitted). The curve has not been srhoothed out, as the slight 

 irregularities may prove to be significant. 



In considering these preliminary results it is in the first place 

 remarkable that caoutchouc should be so transparent to light as 

 to call for the use of so concentrated a solution as 1.5 per cent in 

 a 2-cm. observation tube. 



1-2 



10 



0-8 



0-6 



0-4 



2 



4000 



SSOO 



Wave Length 



3000 



2500 



Ultra-Violet Absorption Spectrum Curve of Ethereal 



Solution of Caoutchouc Calculated on a 3 Per Cent 



Solution in a One-Cm. Cell 



The curve exhibits only a general absorption which is fairly 

 strong for wave-lengths below 2700, but rapidly diminishes with 

 increase in wave-length. 



Neither with the strong solution nor with weaker ones has 

 there been any decisive evidence of absorption bands, but the in- 

 vestigation has not gone far enough to say whether caoutchouc is 

 capable of exhibiting these or not. 



Further work is in progress on different types of rubber and 

 allied compounds with a view to confirming these preliminary 

 observations, and if possible securing some evidence regarding 

 the constitution of caoutchouc. 



'Toiirnal of the Society of Chemical Industry. Jamijiry 31, 19.;1. 

 -Rubber Kesearch A.ssociation, ITniversity College, Londrn. 

 "Procei-dir.Ks cf the Roval S«iety. Ilristol. 89, 329. 

 •Chemical Society Transactinn.s. 1919. 115, 312. 



