January 1, 1913.] 



THE INDIA RUBBER WORLD 



187 



The authors add that a good sample of lithopone should 

 contain not less than 28 per cent, of zinc sulphide. It should 

 he a good white, be smooth and free from coarse particles and 

 have good binding power. 



A NEW RULE OF VULCANIZATION. (Abstract.) 



By A. O. Bourn, Providence, R. I. 



' I 'ME rate at which the combination of rubber and sulphur in- 

 •*• creases or decreases with each increase or decrease of tem- 

 perature, is a point naturally calling for investigation, a knowl- 

 edge of which would be of great value to manufacturers, and 

 would seem to be the foundation of a careful study of the subject 

 of vulcanization. 



To ascertain this ratio of increase or decrease, a large number 

 of experiments were made previous to 1903. with the same com- 

 pound and samples uniform in thickness in most well known 

 processes of vulcanizing. 



The experiments referred to were first made with a compound 

 of 12 pounds dry fine Para rubber, 6 pounds litharge, 6 poimds 

 whiting and 6 ounces of sulphur, giving a proportion of about 

 3 per cent, of the latter. When these samples were submitted 

 to the ordinary dry heat air process, physical vulcanizing effects 

 were obtained approximately as follows : 



IS seconds at 337° F. 13 minutes at 260° F. 



23 " " 326° " 265^ " " 249° " 



25 " '■ 315° " S3 " " 238° " 



1 minute " 304° " IDS " " 227° " 



2 " " 293° " 210 " " 216° " 

 3^ " " 282° " 420 " " 205° " 

 7 " " 271° " ' 840 " " 194° " 



These results seem to establish the rule that for each increase 

 in iemf'erature of about 11° F. during the vulcanizing opera- 

 tion, the velocity of znilcanisation is doubled, end that with each 

 decrease in temperature of about 11° F. the time required for 

 zmlcanisation is doubled. 



.'\bovc 304° the rate of increase is different, there being a 

 marked change in the physical constitution of sulphur ; while 

 below 194° the air process does not produce good results in 

 vulcanization. In other processes down to 161°, there was no 

 difficulty in effecting vulcanization. 



The temperature above 304° showed following results : 325° 

 F, 26 seconds; 350° F, 13 seconds;, 375° F. 6 seconds; 400° F, 

 3 seconds. These and other experiments led to the view that 

 a properly compounded rubber not only vulcanizes at all tem- 

 peratures, but that vulcanization commences immediately upon 

 the compounding. 



In 1904, experiments were made with a view of testing the 

 truth of the proposition that vulcanization proceeds at all tem- 

 peratures. Accordingly samples of Para rubber compounded 

 with from five to seven per cent, of sulphur and fifty per cent. 

 of litharge, were subjected to treatment at temperatures varying 

 from 161° F. to 194° F. in a bath of metal, which fuses at 

 about 150° F. The results confirmed the general rule obtained 

 in the preceding experiments, with the exception that the time 

 required for doubling the velocity of combination was somewhat 

 greater for an increase of 11° F. in the temperature. 



The results of embedding samples of the same compound in 

 a ball of metal, and others in a jar of flowers of sulphur, showed 

 that in seven months the former were thoroughly vulcanized, 

 while in four months the latter were not fully so, but on being 

 exposed to the air became strong and elastic. Samples of 

 both are still available in a state of perfect preservation. The 

 samples had been placed in a room with the average tempera- 

 ture of 110° to 115° F. 



In February, 1912, another series of experiments was com- 

 menced on a line with those of 1904. Similar samples of a 



similar rubber compound and samples of four different grades 

 of rubber shoe compounds, were placed in a ball of fusible 

 metal, in a w-ell-corkcd jar of sulphur, and in two tight jars; 

 one containing a mixture of one part by weight of sulphur with 

 five parts of litharge, and the other containing a mixture of 

 equal parts by weight of sulphur, litharge and "Green Seal" 

 French zinc. Samples of pure, fine Para rubber, free from 

 compounds or mastication, were placed in each jar. 



Of the samples enclosed in fusible metal only one compound 

 was properly vulcanized. All the others were vulcanized very 

 perceptibly less than those embedded in sulphur, sulphur and 

 litharge, or in sulphur, litharge and zinc. The action of litharge 

 and sulphur, as compared with the action of sulphur alone, 

 was very marked ; the vulcanization of all the samples being 

 carried much further than in the case of either of the other 

 experiments. 



An important deduction to be made from the new law of 

 vulcanization and the experiments made in accordance with it, 

 is, that the melting of sulphur has not the slightest effect in 

 changing the rate of vulcanization. Whatever may be the time 

 required to vulcanize a rubber compound at 227° F. it will vul- 

 canize in one-half that time at 238° F, and in one-quarter the 

 time at 249° F. 



Moreover, vulcanization of rubber properly compounded pro- 

 ceeds at all temperatures, whether high or low. At high tem- 

 peratures, the compound may be vulcanized in one second or 

 less, and at low temperatures the vulcanization may proceed 

 so slowly as to escape attention. Samples of these experiments 

 can be examined at the Bourn factory laboratory, at Providence, 

 by anv one wishing to do so. 



A BRIEF HISTORY OF FIRE HOSE SPECIFICA- 

 TIONS IN THE UNITED STATES. (Abstract.) 



By E. A. Barrier, of the Factory Mutual Laboratories. 



A MONG the more important events which led to the develop- 

 ment of the present Underwriters' Specifications for hose 

 was the fact that previous to 1890 it was a matter of common 

 occurrence for length after length to burst at pressures well under 

 100 pounds. 



Steps in the direction of the needed improvement were first 

 undertaken by !Mr. John R. Freeman, then connected with the 

 Inspection Department of the Factory Mutual Fire Insurance 

 Companies, and now one of the foremost hj'draulic engineers in 

 the country, as well as president of several of the individual 

 mutual companies. In experiments conducted in 1888, Mr. Free- 

 man had found that with poor hose a pressure of 95 pounds 

 would be required at the hydrant to produce a good fire stream, 

 while the pressure needed with good hose would be about 7Z 

 pounds ; 200 feet of hose being used in a line. 



After a large number of tests and conferences the first set of 

 Underwriters' Hose Specifications was published in July, 1896. 



The clause requiring 40 per cent, of pure Para gave rise to 

 more discussion than any other in these specifications, but at the 

 time and for several years after "Pure Para" was understood to 

 mean "Fine Para." The whole idea w^as to obtain a list of manu- 

 facturers whose product could be recommended to mills insured 

 in the Factory Mutual Companies. Any manufacturer desirous 

 of being upon the approved list could send in samples for testing, 

 and if they were found to conform with the specifications, his 

 name was placed on the list without charge. 



No changes were made until 1900. and they were then of no 

 great importance. Meanwhile the National Fire Protection .'\s- 

 snciation had been founded and the Underwriters' Laboratories 

 established. In 1899, the National Fire Protection Association 

 had adopted a set of specifications for hose, which were suffi- 

 ciently different from the Factory Mutual Specifications of 1896 

 to cause some confusion among manufacturers. Seeing the de- 



