188 



THE INDIA RUBBER WORLD 



[January 1, 1913. 



sirability of uniform specifications, a "National Standard" was 

 adopted in May, 1902, in which only two important changes were 

 made from the old specifications. One item, regarding the 

 stretch of the rubber lining to five times its original length 

 (which had appeared in the N. F. P. A. specifications) was 

 omitted, and another item requiring a test of 200 pounds on each 

 50 ft. length, not originally in the Mutual specifications, was 

 added. Since that time, the specifications of both organizations 

 have been essentially the same, although their ideas regarding 

 method of enforcement have differed widely. 



The years up to 1911 were occupied with continual tests, dur- 

 ing the progress of which, the paper states, evidence was accumu- 

 lated that most manufacturers of hose were not turning out a 

 product made in accordance with the specifications. The num- 

 ber and character of the analyses and tests gradually changed. 



In 1906 the system of "Label Service" was developed by the 

 Underwriters' Laboratories of Chicago, according to which an 

 inspector would be stationed at the factory, and inspect every 

 length of hose sent out ; a label stating that the hose had been 

 manufactured under the supervision of the laboratory, to which 

 samples could at any time be sent for more detailed tests. Ow- 

 ing to several objectionable features which it was found im- 

 possible to have removed, in spite of a number of conferences, 

 the "Label Service" has never been adopted by the Mutual 

 companies. 



Owing to the opposition of manufacturers, and their objec- 

 tions to using the labels, all those on the "Approved List" of the 

 Chicago laboratories were dropped during 1909 and 1910. In 

 the early part of 1911, however, two of them submitted samples 

 to the Underwriters' Laboratories, which were approved, and 

 adopted the "Label Service." Later in the year another manu- 

 facturer followed. At the present time, it is added, these three 

 are the only ones using the labels. According to the system as 

 developed, the rubber from the beginning of the manufacturing 

 operations, until the hose is completed, is either in the inspector's 

 presence, or under lock ; the key being in his possession. 



After a long series of conferences between the National Fire 

 Protection Association and the manufacturers, a set of specifica- 

 tions was drawn up. which at the time was mutually satisfactory. 

 and allowed a much lower grade of rubber than the present 

 specifications. Owing to a misunderstanding as to their applica- 

 tion these specifications were subsequently cancelled, when a 

 much more stringent set was proposed at the annual meeting of 

 the National Fire Protection Association in May, 1911 and 

 formally adopted in May, 1912. 



Meanwhile, the accumulated experience of the Factory Mutual 

 Laboratories during the last five years, has shown, it is remarked, 

 that much more stringent and definite requirements regarding 

 rubber lining would have to be included in the specifications. A 

 new set was drawn up in the fall of 1910, at the same time that 

 the more definite specifications, already mentioned, were being 

 prepared by the Underwriters' Laboratories for the annual 

 meeting of the National Fire Protection Association of May, 

 1911. Owing to there being some differences between the two. 

 a specification was finally drawn up satisfactory to both associa- 

 tions. This was formally adopted by the Factory Mutual Com- 

 panies in December, 1911, and by the National Fire Protection 

 Association in May, 1912. 



Owing to various delays the Mutual companies have not yet 

 put these new specifications into effect, but in the near future 

 the manufacturers of Underwriters' hose will be notified that 

 after a certain date, hose must be made in accordance with the 

 new specifications; with which some manufacturers have volun- 

 tarily expressed their hearty concurrence. 



The most important change made by the new specifications is 

 a definite call for 40 per cent. "Fine Para" instead of "Pure 

 Para." Tests are specified which the compound must meet, in- 

 cluding acetone extract, free and total sulphurs, alcoholic potash 



extract, tensile strength, elongation and the so-called "permanent 

 set." 



Including this description of the work of the Factory Mutual 

 Companies, which has apparently led to a settlement of the ques- 

 tions at issue, it is remarked that their only object is to make it 

 possible for their members to obtain good hose. The work of 

 testing and inspection is done without charge to the manu- 

 facturers and it has always been the intention to treat them fairly 

 and to co-operate with them as far as they would allow. 



NOTES ON TENSION TESTS OF RUBBER. 



(.-Ibslract.) 



By P. L. Wonnlcy, U. S. Bureau of Standards. 

 ■ I 'HAT the time is now ripe for co-operation between manu- 

 ■*■ facturers and consumers, with a view to uniformity in tests 

 and specifications for goods intended for the same purpose, is 

 shown by the wonderful development of the rubber industry. In 

 the same way uniformity of method is likewise essential for 

 comparing the work of different laboratories; the standardiza- 

 tion of specifications and testing methods being of substantial 

 benefit to manufacturers, consumers and the public at large. 



In each case, the refinement of the methods used should be 

 determined by the nature of the material tested. In this respect 

 rubber constitutes a most interesting field, uniformity in methods 

 being more desirable than extreme accuracy in measurements; 

 while the adoption of uniform testing methods would serve to 

 prevent misunderstandings between manufacturers and con- 

 sumers, arising from specifications being indefinite. 



Opinions differ as to the relative merits of ring and straight 

 test-pieces, the former involving several lengthy operations for 

 their preparations, while the latter are instantly cut out by a 

 single stroke of the die. The ring lends itself to the automatic 

 measurement of elongation, having advantages over straight 

 specimens. When, however, the strength of the rubber varies 

 the ring gives a smaller ultimate elongation than a straight 

 testing-piece. This difference is not always found, but the 

 author's tests on twenty different compounds show a general 

 tendency towards higher values for straight specimens. 



With a view to the encouragement of the testing of rubber 

 goods, the Bureau of Standards has constructed machines 

 combining the greatest simplicity with a reasonable degree of 

 accuracy. For determining tensile strength and elongation, they 

 use an ordinary twin spring dynamometer, attached to the upper 

 end of a metal column, a device being used for preventing recoil 

 by holding the springs under the maximum tension. Two years 

 of continuous service have proved the accuracy of these dyna- 

 mometers. 



As already mentioned, the measurement of elongation at rup- 

 ture is less simple in the case of a straight test piece than with a 

 ring, but a little practice obviates this difficulty. 



Owing to the author's e.xperience of the time consumed in 

 testing the recovery after extension, he constructed an apparatus 

 for testing six specimens at once. 



Of the tensile machines seen in operation by the author, or 

 studied from illustrations, some appear better adapted to experi- 

 mental or research work than to routine testing, this being 

 partly due to their delicate or expensive construction, and their 

 slower operation. 



It would be difficult to obtain by autographic means tension 

 or hysteresis curves for straight test pieces, but another slow, 

 yet otherwise satisfactory method exists of securing curves, that 

 is. by means of a narrow flexible scale of paper or tracing cloth, 

 attached to the test piece by a small spring wire clip. From this 

 scale, one operator reads the elongation at convenient intervals. 

 With a little practice this process becomes exceedingly simple, 

 the curves given clearly showing the characteristics of different 

 rubbers. 



