THE INDIA RUBBER WORLD 



most exactly with the hypothetical straight vulcanization-time 

 curve represented by the dotted line O B in Figures 1 and 2. 



Separate slab cures were then made for physical tests, at the 

 temperatures and times required to produce vulcanization co- 



v:iZATION-TlME Cl 



Temperatures. 



•.CREASING 



efficients of 1.56, 2.96, and 3.86. The results of these tests are 

 shown in the last three columns of Table II. 



Total Time at the 

 Time of Differ- Tensile 



\'ulcan ent. Tempera- Combined Strength. Elonga- Permanent 



izalion. Temps. _ture^ Sulphur. Lbs. per 



Min. Deg. F. 



60 285.5 



107 285.5 



107 285.5 



Sq. In. Per cent. Per ceni 

 2168 715 17.97 



2 — That in vulcanization at a constant temperature, in order 

 to procure ma-ximum physical properties, sulphur must be pres- 

 ent in the mi.xture in such an amount that its active mass is not 

 decreased to an extent which will appreciably slow up the rate 

 of reaction before the desired vulcanization coefficient is attained. 



3 — That for rubber-sulphur mixtures containing 5 per cent or 

 less of total sulphur, the physical properties of the mixture, when 

 vulcanized by a series of increasing temperatures, are superior 

 to those obtained by vulcanization at constant temperature; this 

 is particularly true at vulcanization coefficients of 2.8 or above. 



4 — That the vulcanization coefficient for Hnva rubber is 

 probably between 1.7 and 2.8. 



5 — That it is dangerous to evaluate samples of vulcanized rub- 

 ber solely on the basis of their vulcanization coefficients. 



AIR BRAKES FOR MOTOR TRUCKS AND TRAILERS. 



The use of motor-truck trailers has been limited to light 

 loads and fairly level roads, due to the impossibility of 

 controlling heavily loaded trailers with ordinary brakes. With 

 the application of specially designed air-brake equipment this 

 difficulty disappears and the motor truck and trailer become 

 successful factors in the transportation of interurban freight. 

 This opens a new field of business for the manufacturers of air- 

 brake hose and one that piesents an assured future. 



A two-ton truck and a five-ton trailer with a seven-tun load 

 afforded an exceptional test in a recent trial run where 250 



298.0 

 285.5 

 298.0 

 302.5 

 285.5 

 298. 

 302.5 

 285.5 



To facilitate comparison, the results of these physical tests, 

 together with those obtained at the same sulphur coefficient when 

 vulcanization was effected at a constant temperature of 298 de- 

 grees F., have been grouped together in Table III. From this 

 table it is seen that there is very little difference in the tensile 

 strength of the mixture at coefficients of 1.69 or 2.94 when vul- 

 canized by either method. But in both instances, a series of in- 

 creasing temperatures appears to produce a product of superior 

 elongation. When the coefficient is increased to 3.9, however, it 

 is seen that the product obtained by employing a series of in- 

 creasing temperatures is markedly superior to that obtained at 

 constant temperature, both as to tensile strength and percentage 

 of elongation. 



It is recognized that the results which have been recorded 

 herein are not subject to indiscriminate or general application. 



This work has been confined to the investigation of one 

 rubber-sulphur mixture only, and our calculations have been 

 based on the correct or "technical cure"' of the mixture as being 

 obtained after vulcanization for 60 minutes at 298 degrees F. 

 However, as the comparisons made are relative, and as the prin- 

 ciple involved will apply to other mixtures and other vulcaniza- 

 tion coefficients, we are warranted in drawing the following con- 

 clusions : 



1— That it is possible to calculate and apply a series of in- 

 creasing temperatures such that the vulcanization-time curve for 

 any rubber-sulphur mixture may be made a straight line, the 

 slope of which is dependent on the temperatures employed and 

 the amount of catalyst present. 







^'.*#'" 



■^•^^ij^ 



Truck 



;d Trailer Eouipped 



miles of mountains were encountered with grades as stiff as 

 19 per cent, and four miles long. The fact that the train 

 was held under control under all conditions without damaging 

 the brake linings, speaks well for the brake equipment. For 

 exceptionally severe service, as in construction work, the use 

 of armored hose is contemplated. 



With this equipment the use of pneumatic tires is more 

 appealing to the truck owner, as there is always a reliable 

 means of inflation at hand, and as the pneumatic tire gains 

 prestige in the trucking field, air brakes should be the stand- 

 ard equipment on all trucks, whether a trailer is to be used 

 or not. (The Parker Appliance Co., 2619 Vermont avenue, 

 N. W., Cleveland, Ohio.) 



NO RUBBER STANDARD AT SINGAPORE. 

 In -Singapore there is no official rubber standard, and each 

 person uses the description that he considers most apt. The 

 Singapore unofficial standard of sheet, called "prime," is higher 

 than the London official siandard of sheet, called "f. a. q.," 

 and rubber that would be thrown out in Singapore as not 

 coming up to the level of "priine sheet," might often pass 

 the London "f. a. q." standard. On the other hand, rubber 

 with the marks of a well-known "crack" rubber estate might 

 fetch a premium of a half-penny or so in London over the 

 price for standard quality. That rubber w^ould be "prime" 

 in Singapore. 



