340 



THE INDIA RUBBER WORLD 



[April 1, 1914. 



WHAT THE RUBBER CHEMISTS ARE DOING. 



[Extracts from recent articles on the Cliemistry of Rubber w/iiV/i 

 have appeared in some of the foreign publications.] 



IN the "Kolloid Zeitschrift," Vol. 13, page 265, Spcnce and 

 Young make their seventh contribution on the "Theory of 

 Vulcanization." These authors vulcanized two compounds at 

 temperatures varying from 50 degs. C. to 75 degs. C. at inter- 

 vals of 5 degs. Compound A. which contained 90 parts of 

 extracted plantation rubber and 10 parts of sulphur, after be- 

 ing kept for 90 days at 75 degs. C. contained only 0.32 per 

 cent, combined sulphur. Compound B differed from com- 

 pound A in that it contained 1 per cent, of acetone soluble 

 substances. Compound B showed a regular increase in the 

 velocity of vulcanization, as measured by the combined sul- 

 phur, with increase of temperature. It was not possible to 

 observe any critical tenipcrature at which vulcanization 

 started. From results obtained a temperature cocfticient of 

 2.84 is calculated which is in accordance with that reiiuirfd 

 by a chemical reaction. 



The authors also carried out vulcanization experiments with 

 extracted plantation Para, extracted gutta percha and ex- 

 tracted and purified balata. These substances were com- 

 pounded with 37 per cent sulphur and vulcanized. It was 

 found that these hydrocarbons all vulcanized at the same 

 rate and yielded the same end-product (CioHjoSnln of identical 

 physical properties. As results of these experiments the au- 

 thors conclude that the vulcanization of Para, gutta percha 

 and balata is a catalytic chemical reaction, that vulcanization 

 takes place at all temperatures, and that the same compound 

 (C,„H„S.')n is always formed, provided there is an excess of 

 sulphur. 



In the "Gummi Zeitung." Vol. 28, page 747, E. Fickendey 

 contributes an article "On the Eflect of Scraping the Manihot 

 Tree on the Yield of Rubber Obtained." In this article at- 

 tention is called to the German patent No. 265.937 issued to 

 the government of Cameroon for a process for increasing the 

 yield of latex of the Hevea brasiliensis. The process consists 

 in scraping, prior to tapping, the external portions of the bark 

 as far as the green cork cambium. This scraping is repeated 

 at definite periods of time during the tapping season. Trees 

 so scraped nearly always yielded twice the normal output of 

 rubber and in some cases four times the amount. 



In the case of Kickxia, it was found that this scraping had 

 no effect on the yield of latex and it is suggested that this 

 fact is probably connected with the observation that the 

 Kickxia tree does not exhibit what is known as wound reflex. 

 It was therefore of interest to determine whether a tree such 

 as the Manihot, which does exhibit the property of wound 

 reflex, would be affected by this scraping of the bark. It was 

 actually found that this scraping process did materially in- 

 crease the yield of latex in the case of the Manihot, altho the 

 increase was not quite so marked as in the case of the Hevea. 



In the "Journal of the Society of Chemical Industry." Vol. 

 XXXII, page 1041, W. A. Caspari contributes an article on 

 the "Composite Nature of Raw India Rubber." Attention has 

 been called by previous investigators to the fact that crude 

 rubber is not completely soluble in the usual solvents and 

 that it consists of a soluble and an insoluble portion. Caspari 

 found that by using petroleum ether, B.P. 40 to 65 degs. C. 

 a very satisfactory separation of the component parts of the 

 rubber could be effected. By means of this solvent it is pos- 

 sible to obtain two distinct bodies, which may be described 

 as soluble and insoluble rubber. The soluble portion is a 

 colloid of relatively slight mechanical strength and has a pro- 

 nounced tendency to become soft and sticky, especially on the 

 application of heat. With solvents it forms a transparent 

 solution and does not swell very materially prior to solution. 

 The insoluble pectous portion is a colloid of considerable 



elasticity, with a tendency to retain its structure in the presence 

 of solvents, tho subsequently swelling to a "jel," usually 

 with increase in volume. Both portions arc doubtless con- 

 stituted of the same hydrocarbon and have about the same 

 specific gravity. The author constructed an apparatus for 

 determining quantitatively the amounts of these two con- 

 stituent parts of the rubber and gives the results of the de- 

 terminations carried out with a variety of crude rubbers. 



MANUFACTURE AND PROPERTIES OF SUBLIMED 

 WHITE LEAD. 



OUliLIMFU white lead is the commercial name for the basic 

 '-' sulphate of lead produced by the oxidation of galena, the 

 sulphide of lead, under the intense heat of an oxidizing atmos- 

 phere. The violence of the combustion produces a white sub- 

 limate, which, when purified, is known as sublimed white lead. 



Commercial sublimed white lead, however, contains a higher 

 percentage of lead sulphate than is required for its theoretical 

 formula, conditions l)cing so adjusted that a ooni[i(>und is ob- 

 tained showing about 16 per cent, of lead oxide. 



Sphalerite or sulphide of zinc is present in nearly all non- 

 argentiferous lead ores, and when it produces zinc oxide to the 

 extent of about 6 per cent., enhances the value of the pigment 



Hard coke is used as fuel, with metallic iron and limestone 

 as fluxes, together with the silica present in the ore. Blue Fume 

 (or sublimed blue lead), which is frequently used as additional 

 charge material, is formed in the smelting of lead ores, and is 

 found to contain about 35 per cent, of lead oxide and about 

 50 per cent, of lead sulphate. According to Mr. John A. 

 Schaeffer, of the Pichcr Lead Co., Joplin, Mo., this fume pigment 

 (or sublimed blue lead), ground in oil, is being rapidly adopted 

 fur the protection of iron and steel. 



The o.xidizing furnaces (two of which are considered a unit) 

 consist of oval iron water-jackets on a solid brick base, with a 

 small tap-hole for tlie continuous removal and sorting of slag 

 and metallic lead. Immediately upon feeding the charge into 

 the furnace, the temperature of wliich is maintained at a point of 

 incandescence, sublimation occurs with great violence, the vola- 

 tdized lead passing upward into the combustion chamber. A 

 powerful fan draws the condensed fume onward through the 

 cooling system into the bag room, which is of a special type 

 somewhat like those used for the collection of all fumes. In 

 this room are three rows of hoppers, each carrying 24 bags. The 

 gases are forced through the cloth of the bags, while the sub- 

 limate is deposited. 



Sublimed white lead as removed from the hoppers is white 

 in color. It consists of very fine amorphous particles, about 

 1/35,000 of an inch in diameter, its specific gravity being 6.2. 



Its composition is approximately 78 per cent, lead sulphate, 

 16 per cent, lead oxide and 5.5 per cent, zinc oxide. The lead 

 oxide present is chemically combined as a basic sulphate of lead, 

 the sulphate of lead in excess of the amount required for the 

 theoretical formula being held by practically all authorities to 

 be neutral sulphate of lead. 



In common with other white lead compounds, sublimed white 

 lead is most valuable as a paint pigment when compounded 

 with zinc oxide and a small percentage of inert crystalline pig- 

 ment. It is being extensively used in compounding the finer 

 grades of rubber goods. Moreover, it practically inhibits the 

 corrosion of iron and steel, when applied as a protective coating, 

 even after long exposure, thus preventing decay by eliminating 

 ilie cause which destroys the metal and lengthening its life as a 

 structural material. 



Should be on every rubber man's desk — Crude Rubber and 

 Compounding Ingredients ; Rubber Country of the Amazon ; 

 Rubber Trade Directory of the World. 



