580 



THE INDIA RUBBER WORLD 



May 1, 1921 



action was followed only by the gradual disappearance of sulphur 

 into combination. The composition of the original mixture was 

 sulphur (SX) 10.4 per cent, methyl-rubber 89.6 per cent. Ex-. 

 pcrimcnts were made at 168 degrees, 178 degrees, and 188 degrees 

 C. 



It is remarkable that the disappearance of most of the sulphur 

 into combination appears to follow the approximately rectilinear 

 course already observed with natural rubber. If, as suggested by 

 van Iterson, this is due to autocatalysis it is evident that the non- 

 caoutchouc constituents of natural rubber are not responsible. 



The results are not quite as smooth as could be desired, but if 

 comparison is made of the time required for the attainment of the 

 various degrees of vulcanization at different temperatures, the 

 temperature coefficients in each case are greater for the interval 

 168 degrees— 178 degrees than for 178 degrees— 188 degrees. 



The apparent slight increase in the temperature appears to in- 

 dicate the existence of a very brief initial period of greater re- 

 activity. This may be due to the fact that the sulphur initially 

 is composed practically entirely of S?^, which rapidly undergoes 

 conversion into the less active equilibrium mixture ; it might, 

 however, be caused by the presence in the synthetic rubber of a 

 small proportion of some more active material. There is nc 

 such regular alteration observable in the figures calculated in a 

 similar way from the experiments with ordinary rubber and sul- 

 phur at 138 degrees — 168 degrees C. 



A better comparison of the temperature coefficients is probably 

 given by the ratio of the tangents of the angles included between 

 the horizontal axis and the line between the origin and the point 

 representing the end of the "rectilinear" course of the vulcaniza- 

 tion process. This method of comparison likewise shows a 

 smaller increase in the rate of reaction for the second interval. 



Time (minutes) Tenii'eraturc coeificient 



Vulcanizing I6S° 178° 188° 178°-168° 188°-178° 

 coefficient 



4 2.i 14 — 1.8 — 



5 34 18 10 1.9 1.8 



6 43 21 11 2.0 1.9 



7 S2 24 12 2.2 " 2.0 



8 61 28 14 2.2 2.0 



9 73 31 15 2.4 2.1 



angle 33° -,6' 71° — — 



tan, angle 0.65 1.48 2.O0 2.3 2.0 



The smaller coefficient for the higher temperature interval sug- 

 gests that the sulphur equilibrium mixture at the higher tempera- 

 ture is relatively less effective than the equilibrium mixture ex- 

 istent at the lower temperature; as the difference in the composi- 

 tion of the two equilibrium mi.xtures will be a smaller proportion 

 of S^ and a greater proportion of St and Si^ at the higher tem- 

 perature, and as the earlier considerations lead to the view that 

 the effectiveness of St is very little different from that of S^, 

 it follows that the results again indicate a somewhat inferior 

 vulcanizing capacity for S/*. It must be remembered, however, 

 that the observed dififerences in such experiments, based on the 

 relative activity of interchangeable modifications of a chemical 

 substance, will be diminished by the tendency of the equilibrium 

 automatically to adjust itself as the more active form disappears. 



Although these results indicate a difference between the ac- 

 tivity of Sf^ and of S^ or St the outstanding fact is not the exist- 

 ence of this difference but its relatively small magnitude. The three 

 forms are of such diverse general characteristics that much 

 greater differences mighf have been expected. Under the con- 

 ditions of ordinary technical practice indeed, the possibility of 

 alteration in the relative proportions of the various modifications 

 of sulphur is not likely to form an appreciable disturbing factor 

 in vulcanization, and the only instance of any special form of 

 sulphur (as such) showing special vulcanization features appear.'; 

 to be that possibly involved in the recently discovered method 

 of treating raw rubber with sulphur dioxide and hydrogen sul- 

 phide. 



METHODS OF ANALYSIS 

 DETERMINATION OF ANTIMONY IN RUBBER GOODS 



THE METHOD for determining antimony in rubber goods as 

 given by S. Collier, M. Levin, and J. .\. Scherrer\ follows: 

 The sample (0.5-gram) is extracted with acetone and, if 

 mineral oil or "substitute" is present, further with chloroform 

 until the extract is no longer colored ; after drying in a vacuum, 

 the material is heated with 25 cc. cymene at 130 degrees — ■ 140 

 degrees C. in a 300 cc. flask until the rubber has completely dis- 

 solved ; the cooled liquid is diluted with 250 cc. of light petroleum 

 spirit (maximum boiling point 45 degrees C.) and the mixture 

 left overnight, being then decanted through a Gooch crucible. 

 .'\fter washing ten times with petroleum spirit the residue is 

 dried and shaken with 30 cc. hydrochloric acid, until the antimony 

 sulphide has passed into solution. The solution is filtered slowly 

 through the dried Gooch crucible and after dilution, the antimony 

 is precipitated with hydrogen sulphide. The antimony is tlien 

 estimated, e. g., by heating with 12 to 15 cc. sulphuric acid and 

 5 grams potassium sulphate in a Kjeldahl flask until a colorless 

 solution is obtained, diluting to about 100 cc. with water, adding 

 20 cc. hydrochloric acid and 1 to 2 grams sodium sulphite, boiling 

 to expel all sulphur dioxide, and titrating with tenth normal per- 

 manganate. 



DETERMINATION OF TOTAL SULPHUR IN RUBBER 

 The following methods for nibber analysis are given by A. R. 

 Pearson in Amlyst. 1920, 45. 405-409. 



Twenty cc. of nitric acid (sp. gr. 1.5) is placed in a flask and 

 0.5-grani of the rubber is added in small pieces at a time ; the 

 mixture is heated gradually and kept on a water-bath for 30 min- 

 utes. Small successive quantities of permanganate are added 

 until some manganese oxide remains unreduced after one hour's 

 heating, 20 cc. of concentrated hydrochloric acid is added, the 

 mixture again heated, evaporated to dryness, the residue treated 

 with hydrochloric acid, again evaporated, the residue treated with 

 hot dilute hydrochloric acid, the solution filtered, and the sul- 

 phuric acid in the filtrate determined gravimetrically. 



DETERMINATION OF CARBONATES IN RUBBER MIXINGS 

 One gram of the finely divided sample is heated with 25 cc. of 

 glacial acetic acid in a flask provided with a short reflux con- 

 denser, the latter being connected with a U-tube containing solid 

 lead acetate, a U-tube containing in one limb sodium acetate and 

 in the other calcium chloride, and two weighed tubes containing 

 soda-lime and calcium chloride. The contents of the first two 

 U-tubes must be saturated with carbon dioxide before use. A 

 current of air is aspirated throu.gh the apparatus during the whole 

 operation. 



'Tlie IndiaRiiblier Journal, 1920, 60, 1297-1298. 



CHEMICAL PATENTS 

 THE UNITED STATES 



RUBBER Mix and Process of Comi'oij'ndixg Rubber, consisting 

 in adding to rubber, water carrying in suspension hydroxide 

 of aluminum, mi.xing the water and aluminum hydroxide with 

 the rubber, driving off the water, and heating the mix with a 

 vulcanizing agent to effect vulcanization. — Robert C. Hartong, 

 assignor to The Goodyear Tire & Rubber Co., both of Akron, 

 Ohio. Umted States patent No. 1,370,965. 



Heat-Ixsulating Matekial and Method of Making It. 

 Heat insulating material capable of maintaining its rigidity, at 

 ordinary temperatures of artificial refrigeration the material being 

 cellular and of approximately the following composition : asphalt- 

 um 27.0; infusorial earth 11.0; magnesium carbonate 5.0; crude 

 rubber 26.9; sulphur 14.9; sulphur treated corn oil 2.6; petrol- 

 eum tailings S.S; bicarbonate of soda 6.0; alum O.S.^Clark H. 

 Bennett, Chicago, Illinois, John F. Palmer, St. Joseph, Michigan, 

 and Frank V. Wedlock, Chicago, Illinois, assignors to Bentex 

 Co., Chicago, Illinois. United States patent Xo. 1.371.016. 



