November 3, 1922] 



SCIENCE 



519 



cured at different temperatures. The relationship 

 between the temperature developed and the per 

 cent, combined sulfur is given. 



Zinc oxide in a new physical condition — its 

 effect upon rubber compounds: Frank G. Breyek. 



Beactions of accelerators during vulcanization. 

 V. Dithiocarbamates and thiuram disulfides: 

 G. W. Bedford and Hakold Gray. The metallic 

 dithiocarbamates are true accelerators of vulcan- 

 ization. Metallic oxides are necessary to prevent 

 the decomposition of the metallic salts by hydro- 

 gen sulfide or to reform them after decomposition. 

 Hydrogen sulfide changes thiuram disulfides to 

 dithiocarbamates and decomposes the metallic 

 salts. Ammonia increases the curing power of 

 both thiurams and zinc dithiocarbamates. These 

 views are supported by chemical data olbtained in 

 the laboratory in the absence of rubber. 



A method for the measurement of resistance to 

 tear in vulcanized rubber: Erle C. Zimmerman. 

 A method is presented for measuring the re- 

 sistance to tear of vulcanized rubber in terms of 

 work. In this test a sheet of rubber 0.1 inch 

 thick is supported between hooks on the ordinary 

 tensile testing machine, and an autographic chart 

 is taken as the rubber is torn. Eesistanee to tear 

 is expressed as inch-pounds per square inch of 

 rubber torn, in the formula, 



Fe 



W = KA 



2 



Lt 



in which "K" is a constant, "A" is the work 

 area on chart, "L" is the distance torn, "t" is 

 the thickness, "e" and "F" are the elongation 

 and force in equilibrium at the end of the test. 

 Some data are given of resistance to tear in zinc 

 oxide and pure gum stocks. 



The results of variation in the sulfur and hexa- 

 methylenetetramine content on some of the prop- 

 erties of compounded rubber: H. A. Depew. A 

 non-blooming compound must not contain more 

 than 1 per cent, of free sulfur calculated on the 

 rubber. Using hexamethylenetetramine as an ac- 

 celerator, the tensile strength, elongation and 

 maximal area under the stress-strain curve 

 increase with a decrease in the amount of sulfur 

 used, and to a lesser extent are increased by 

 using a large amount of accelerator. The shape 

 of the stress-strain curve is not affected by the 

 sulfur and accelerator content. The vulcaniza- 

 tion coefficient at the optimum cure depends on 

 the sulfur content. 



An abrasion machine by which comparative 

 wear tests can be made on laboratory test pieces 



or on sections out from tire treads: H. A. Depew. 

 A simple abrasion machine is described, on which 

 laboratory test pieces or sections cut from tire 

 treads can be tested for comparative resistance 

 to the abrading or rasping influence of surfaces 

 of known composition. The test pieces fastened 

 at one end, only, are held against a common, 

 uniformly moving, abrading surface with a def- 

 inite uniform pressure. The effect of pressure 

 upon the test piece and the effects of speed and 

 composition of the abrading surface are dis- 

 cussed. A comparison of this method of testing 

 with the loose abrasive method is given. Com- 

 parisons by service tests (tires and heels) are 

 also made. 



The influence of certain compounding ingre- 

 dients in hard rubber: "W. E. Glancy. Several 

 articles have been published showing the action of 

 compounding ingredients in soft rubber goods. 

 Very little has been published thus far with re- 

 gard to the principles of hard rubber compound- 

 ing. Graphs are shown which indicate the mass 

 action effect of sulfur, the curing properties of 

 lime and magnesia and the loading qualities of 

 M. E., tire reclaim and resin in hard rubber mix- 

 tures. 



A convenient nomograph for rubber chemists: 

 W. R. HicKLER and W. E. Glancy. Rubber 

 chemists have frequently use for tables which 

 will be available for converting the cure of a 

 rubber stock from a known temperature and time 

 to a different temperature with corresponding 

 time. A formula has ibeen worked out from ex- 

 perimental values and a nomograph constructed 

 whereby it is possible to quickly find the desired 

 cure. 



Bubber softeners: P. M. Aultman and C. O. 

 North. The action of rubber softeners on rubber 

 itself has received very scant attention from 

 rubber chemists. The writers in an effort to find 

 out this action heated vulcanized rubber in each 

 of a large number of softeners until total disinte- 

 gration ensued. The comparative rate of dis- 

 integration was also observed by means of a test 

 in which the swelling of the rubber in the soft- 

 eners was measured. This method was checked 

 roughly. Sulfur, accelerators and both together 

 were added successively to the softeners to find 

 out their effect on the action, with the results 

 that in each case there was an increase in the 

 rate of solvation. The state of cure was also 

 found to have ' an effect on the results, as the 

 rate of solvation was found to be inversely pro- 

 portional to the cure. Mixtures of softeners were 

 found to have, in many cases, the average proper- 



