

THE INDIA RUBBER WORLD 



[August 1, 1915. 



What the Rubber Chemists Are Doing. 



FRANK GOTTSCH, of the Mt. Prospect Laboratory, De- 

 partment of Water Supply, Gas and Electricity, ( ity of 

 N'ew York, publishes in "The Journal .■!" Industrial and 

 Engineering i hemistry," July. 1915, an article on "Specification 

 ulcanized Rubber Gum by Volume and Its Determination 

 by a New Solution Method." Detailed methods of test and 

 anah jiven, which contain certain matter original with 



die author under the headings of "Mineral Fillers," "Foreign 

 Mcob lii Potash Extract," "Vulcanized Rubber Gum by Weight" 

 Vulcanized Rubber Gum by Volume." His method tor 

 Sulphur" is novel in the application of a well-known 

 method for total sulphur to the free sulphur determination. 



ANALYSIS. 

 Freb Si lphur. The dried acetone extract is entirely trans- 

 ferrei .c. iron or nickel crucible by acetone, choloroform 



or benzol, and the solvents evaporated off on the steam hath and 

 ci grams of potassium carbonate and 4 grams of sodium per- 

 added. Mix, cover, heat at low temperature over 

 "- shield i" avoid sulphur fumes, until the mixture fuses, 

 then bring to quiet fusion for 15 to 20 minutes. Avoid rapid 

 heating and explosions and rotate the melt while solidifying. 

 When cool put crucible and cover into a casserole with 200 c.e. 

 of water, add 5 to Id c.e. bromine water and boil melt till dis- 

 solved. Settle, decant, filter and wash through thick filter with 

 hot water. Cool, acidifj filtrate with dilute hydrochloric acid, 

 make up to -Iiiii c.e. and precipitatf boiling with Id c.e. of 10 per 

 i nl si ilution of barium chloride. 



FILLERS. — A one-gram sample is extracted by acetone 

 our hours and the rubber dried in the water oven at 100 de- 

 i entigrade until the odor of acetone is gone. Transfer 

 tin sample to a 100 c.e. beaker, burn the thimble to ash and add 

 it to the beaker. \dd 50 c.e. of clear molten salol and heat the 

 i on the hot plate at a temperature of not less than 120 

 noi more than 150 degrees ("entigrade, stirring occasion- 

 ally until the rubber is apparently dissolved. After settling, 

 transfer the liquid to a 200 e.e. beaker and if the residue in the 

 small beaker contains particles of undissolved rubber more salol 

 i- added and sedation completed. Stir 2 c.e of a 1 per cent. 

 solution of soluble cotton in amyl acetate into the warm liquid 

 in the 200 c.e. beaker, cool and add redistilled turpentine until 

 iod "flock" has formed, adding at least 75 c.e. of turpentine 

 with constant stirring. Allow the liquid to stand until the flock 

 The supernatant liquid is decanted and filtered by sue- 

 through an alundum crucible placed in a Spencer holder, 

 i the flock bj decantation with turpentine, filtering the lat- 

 ter; transfer the whole to the crucible, then dissolve carefully 

 in a fev i - of acetone, and wash the tillers with acetone, being 

 careful not to allow the tillers to cover and clog the sides of 

 tin crucible. All beakers and the crucible are to he thoroughly 

 washed with acetone. Dry to constant weight at 105 to 110 de- 

 ( entigrade, cooling in a desiccator. Evaporate all the 

 filtrate and washings, transfer to a weighed porcelain dish, burn 

 rganic matter. Add weight of residue to that .if the 

 idlers in the crucible and calculate as "mineral fillers." 



Fori i iholk Potash Extract. — The dry rubber residue 



from tin acetone extract is extracted with 50 c.e. of alcoholic 

 potash, stoppered, in an air oven kept between 105 and 110 de- 

 vice- Centigrade for 4 hours. Cool, filter and wash the residue 

 clean with hot absolute alcohol. Precipitate potassium chloride 

 by acidifying filtrate strongly with hydrochloric acid, settle, (fl- 

 ash with hot chloroform and evaporate the filtrate on 

 in bath till odor of hydrochloric acid just disappears. Take 

 up residue with chloroform, filter ami wash with hot chloroform 

 inn- 3 beaker, and evaporate t . . dryness. If the residue is not 



oil) "r greasj t.. touch, it may he disregarded. If oily or greasy 

 the residue is washed with small portions of 88 degrees Beamme 

 naphtha, filtered through a washed plug of cotton into a small 

 weighed beaker, evaporated and dried in water oven at 95 to 

 100 degrees (entigrade in 15-minute periods until the weight is 

 constant, or increases. The result is calculated as "foreign al- 

 coholic p. -tash extract." 



Vulcanized Rubber Gum by Weight. — Subtract the sum of 

 the percentages of free sulphur, organic acetone extract, min- 

 eral tillers and corrected foreign matter from 100 per cent. 

 The balance is the vulcanized rubber gum by weight. 



\ i lcanized Rubber Gum by Volume. — Multiply the percent- 

 age by weight of vulcanized rubber gum by the specific gravity. 

 The product is that specified by the term vulcanized rubber gum 

 by volume. 



The author in his discussion states that his method for free 

 sulphur is designed to absolutely obviate the influence of organic 

 matter by its complete removal. Concerning estimation of min- 

 eral tillers, it is found that salol will dissolve soft rubber in less 

 than an hour ami vulcanite in from two to three hours. Owing 

 to the condition of extreme fineness met with in many of the 

 mineral fillers of rubber a coagulant is found necessary to filter 

 them off. even through an alundum crucible. Such a coagulant 

 is found in soluble cotton dissolved in amyl acetate. After dis- 

 covering in salol a suitable solvent for vulcanized rubber gum, 

 difficult) was experienced in finding a diluting agent which would 

 not reprecipitate the rubber. Ether, chloroform and turpentine 

 were the only satisfactory ones found. Of these only turpentine 

 satisfactorily reprecipitates the soluble cotton used to form a flock 

 suitable for filtration. 



Vulcanized rubber gum by weight represents the pure gum 

 (free of resin, ash, moisture and air) plus its combined sul- 

 phur. It is this vulcanized rubber gum that gives rubber goods 

 their specific and desirable properties, and it is consequently 

 specified and determined. 



Vulcanized rubber gum by volume is more properly related 

 P. the physical properties and quality of rubber compounds than 

 is the percentage by weight. This volume conception is ni 

 sary to an undertsanding of rubber mixings. The specific gravity 

 of vulcanized rubber, without mineral fillers, has been shown to 

 be safely taken at unity. No closer method of determining tin 

 volume is necessary than to multiply the percentage by weight 

 of vulcanized rubber gum present by the specific gravity of the 

 compound. This volume would be strictly correct if divided by 

 the true specific gravity of the vulcanized rubber gum present, 

 hut the factor obtained as specified expresses the true volume 

 close enough for practical needs. 



The minimum vulcanized rubber gum by volume that will give 

 a sound article can hardly he less than 55 per cent, if made up 

 of rubber, sulphur and mineral fillers only. Eess than this 

 amount needs such materials as resins, oils, waxes or asphaltums 

 to iill the pores between the particles of fillers. As the volume 

 percentage id' vulcanized gums decreases in a compound com- 

 posed of rubber, sulphur and mineral fillers only, the liability of 

 decay l.v oxidation increases. By specifying a minimum per- 

 centage by volume of vulcanized rubber gum the choice of tillers 

 is left entirely to the manufacturer, as it should be. Whether 

 be uses light or heavy fillers is immaterial as long as the volume 

 specified is obtained and the chemical and physical requirements 

 are met. The same result can he obtained by fixing a minimum 

 specific gravity and a minimum percentage, by weight, of vul- 

 canized rubber present, hut the kind of fillers would then be 

 limited to a few having a certain density. The method specified 

 permits any manufacturer to make as good a compound as he 



