658 



THE INDIA RUBBER WORLD 



June 1, 1921 



unity. The following table contains the values obtained with 



10 per cent sulphur, 2 per cent accelerator and ISO per cent zinc 



oxide or its equivalent voUinic of other tiller based on 100 parts 



of rubber : 



Base stock 1.00 



Zinc oxide (150 per cent) 1.65 



Glue 87 



Asbestine 91 



Lampblack 1.02 



Gas black 1.14 



Crimson antimony 1.15 



Whiting 1.23 



Lithoponc 1.33 



Magnesium carbonate 1.45 



Soapstone 1.45 



Clay 1.67 



Litharge 1.78 



Red oxide 1.86 



Fossil flour 1.90 



Barytcs (ground) 2.28 



Barytes (precipitated barium dust) 2.65 



Frictioned fabric 1.07 



The state of cure of the various stocks was found to have no 

 effect on tlie conductivity. 



REACTIONS OF ACCELERATORS DURING VULCANIZATION— III 



CARBO-SULPHYDRYL ACCELERATORS AND THE 



ACTION OF ZINC OXIDE - 



By C. W. Bedford and L. B. Sebrell 



Reactions of accelerators producing mercapto groups by action 

 of sulphur are discussed. ThiocarbaniUde with aniline in benzol 

 solution will dissolve zinc oxide and will vulcanize a zinc oxide 

 cement at room temperature. Other zinc salts of mercaptans, 

 such as zinc thiophenol and zinc-ethyl-xanthate, will vulcanize 

 pure gum cements containing sulphur at room temperature. 

 These accelerators are free from nitrogen or alkali and also 

 function in press or steam cures. Without zinc oxide no accel- 

 erator has been found which will vulcanize at room temperature. 

 Zinc salts of carbo-sulphydryl accelerators furnish the key to 

 the paper. 



RAPID BOMB METHOD FOR DETERMINING SULPHUR IN 



RUBBER COMPOUNDS 



By W. W. Evans and Ruth Merling 



A new method for determining sulphur in rubber compounds. 

 The sample consists of 0.2-gm. of rubber suitably packed ii; 

 sodium peroxide with a little sugar and potassium chlorate on 

 top. Ignition is secured in a Parr calorimeter. The total time 

 for running a determination was placed at three hours. Results 

 follow : 



Sulphur 

 Incorporated 



3.50 

 6.35 



Nitric Acid- 

 Bromine Bomb 

 Method Method 

 . . 2.23 2.39 

 . . 2.75 2.98 

 . . 3.55 3.73 

 . . 6.41 6.36 



The method works with high amounts of sulphur, as in an 

 antimony tube or hard rubber analysis. A blank should be run, 

 as chemically pure sodium peroxide sometimes contains sodiuin 

 sulphate. 



VOLUME INCREASE OF COMPOUNDED RUBBER UNDER STRAIN 

 By Henry Green 

 At the Philadelphia meeting a year and a half ago, H. F. 

 Schippcl pointed out that compounded rubber increases in volume 

 when strained. He demonstrated this fact by indirect methods. 

 The present author has been able to observe and photograph, by 

 means of the microscope, the actual changes which take place. 

 Working with rather coarse barytes, he obtained cavities at 

 either end of the barytes crystals. He noted that some particles 

 developed cavities when the piece containing them was stretched, 

 but some did not. In seeking an explanation of this, he advanced 

 the theory that many of the particles were surrounded with an 

 adsorbed film of air. In such cases the rubber did not adhere 

 to the crystal. In other cases, when this film was absent, there 

 was adhesion between the rubber and crystals and no cavities 

 were obtained. Referring to zinc oxide, Air. Green stated that 



in a stock containing 100 volumes of zinc oxide to 100 volumes 

 of rubber, no agglomerates were discernible under the microscope. 



ROUND TABLE DISCUSSION 

 FACTORY CONTROL OF VULCANIZATION 



.\ simple form of apparatus for comparison of thermometers 

 used on vulcanizers and curing presses was described by Arnold 

 H. Smith. It consists of a wrought-iron pipe three or four 

 inches in diameter and about three feet long with capped ends, 

 arranged for steam inlet and drainage. A number of openings 

 are provided on the top and one side of the pipe for receiving 

 the thermometers to be compared with the correct or standard 

 instrument reserved for reference. This device is practically the 

 same as one illustrated and described in The India Rubbek 

 World, June 1, 1904. 



In the discussion it was noted that to render the tests reliable 

 a pet-cock should be provided at each thermometer connection to 

 insure venting trapped air and provide circulation of steam 

 around the thermometer bulb. 



TESTING CRUDE RUBBER AS RECEIVED AT THE FACTORY 



Sampling a lot of crude rubber for test is either a matter of 

 selecting from each bale and averaging, or selecting portions 

 from the broken down averaged lot and averaging again for test 

 purposes. 



The view was advanced that test of the curing quality of crude 

 rubber should be: (1) by compounding with zinc oxide, sulphur 

 and an organic accelerator, or, (2) by compounding with litharge 

 and sulphur. Dr. G. S. Whitby suggested that stress-strain 

 curves will be found very illuminating in connection with judging 

 the curing value of crude rubbers. 



REACTIONS BETWEEN SULPHUR AND VARIOUS SOFTENERS 



This topic did not elicit much comment, except that the 

 function of softeners in compounding was principally to augment 

 plastic flow in the mixing. Dr. Bingham, of Lehigh University, 

 Easton, Pennsylvania, and Henrj' Green of The New Jersey Zinc 

 Co., have published researches on the subject of plastic flow. 



PHYSICAL TESTING COMMITTEE 



A new physical testing committee was appointed as follows : 

 C. Olin North, chairman ; W. J. Wiegand, S. Collier, E. H. Graf- 

 ton, and H. E. Simmons. This committee was instructed to coa 

 sider the standardization of methods of plotting stress-strain 

 curves and other data, standardization of experimental mixings, 

 and testing of various rubbers and other materials. .\n investiga- 

 tion of new methods of physical testing was advocated for better 

 judging degrees of vulcanization for the probable life of rubber 

 compounds. 



SHOE BILL PROHIBITS LEATHER SUBSTITUTES UNLESS 

 LABELED 



The Caulfield bill recently referred to the Committee on General 

 Laws of the State of New York amends the general business law 

 regulating the sale of boots and shoes, and adds the following new 

 sections, to lake effect September 1, 1922: 



Unlawful Sale: No person, association or corporation, 

 within this state, shall sell, offer or expose for sale any boot 

 or shoe with a counter, sole, insole, middle sole or slip sole 

 made in whole or in part of leatherboard, strawboard, leather- 

 oid, libreboard, horn fibre, pate or any other substitute for 

 leather whatsoever, without printing upon a tag securely 

 affixed to each boot or shoe, in plain sight and in the English 

 language, stating what substitute for leather, if any, has been 

 used, designating each part of such boot or shoe where such 

 substitute has been used. And if no substitute for leather 

 has been used, the tag shall bear a statement to that effect. 

 The removal of such tag upon a sale, exposure or offer of 

 sale of any hoots or shoes by any person other than by the 

 purchaser shall he deemed a violation of this article. 



ExcF.PTioNs: This article shall not be construed to apply to 

 the use of a rubber heel on any boot or shoe, or eyelets, or 

 straps used to assist in pulling on the boot or shoe. 



