426 



THE INDIA RUBBER WORLD 



[May 1, 1919. 



very inflammable. This was the case, lor example, with alumi- 

 num dust (see Technical Paper 152 of the Bureau of Mines). 

 Probably the failure to ignite these dusts is due to the fact that 

 the heat coil has too little heat capacity to heat the dust suffi- 

 ciently in the short time of contact. Experiment seems to 

 justify this explanation, since aluminum dust, when poured into 

 or blown across a small earthenware dish heated to 800 degrees 

 C. has been found to ignite readily, with a blinding flash. This 

 latter test was tried with the carbon black, but, when poured 

 into a dish heated to 1100 degrees C, this dust gave no ignition 

 whatever. 



There is being developed in the Pittsburgh laboratory a dust 

 explosion gallery in which it is hoped that the explosibility 

 tests at the experimental mine can be duplicated. The gallery 

 is not j'et completely standardized, but the work has been 

 carried far enough so that tests of linely divided dusts can be 

 made. In this gallery a prearranged dust cloud is formed by 

 the explosion of a small charge of powder which blows the 

 dust into the gallery from a number of jets arranged throughout 

 the length of 14 feet. A second powder shot ignites this dust 

 cloud. Very inflammable dusts are ignited by a quiet flame 

 produced by the burning of ten grams of rifle powder piled 

 loosely on the floor of the gallery at the rear. Dusts not so 

 inflammable can be ignited under high pressure in the gallery. 

 This pressure is obtained by stopping down the front end of 

 the gallery and greatly increasing the force of the powder shot 

 through loading the powder into a small cannon. 



It was found that the gas black would easily ignite and 

 readily propagate a flame under the conditions first described, 

 when the gallery was loaded with 12-gms. per cubic foot of 

 space. This easy ignition was probably due to the fact that the 

 concussion of the dust-raising shot separated the gas black and 

 caused a good mixture with the air. 



Experiments were then conducted to determine the amount 

 of shale dust which it was necessary to add to the gas black 

 to make it non-explosive under the conditions at the experi- 

 mental mine. This was done in order to make a comparison of 

 its explosibility with that of Pittsburgh coal dust. By using 

 the second method outlined for the experimental gallery, it was 

 found that a mixture of 60 per cent by weight shale dust and 

 40 per cent gas black would just fail to explode under mine 

 conditions. Since the corresponding mixture of shale dust and 

 coal dust is 75 per cent shale and 25 per cent coal, the gas black 

 appears to be nearly as inflammable as coal dust, if the right 

 conditions are obtained for its ignition. 



SUMMAHY or CONCLUSIONS. 



The above experiments show clearly that the sample of gas 

 black is not easily ignited, but that, if conditions are right for 

 ignition, it is very explosive. In other words, the gas black 

 can be classed with dangerous factory dusts. 



The object of the parade is to symbolize the various elements 

 that make up American life. 



All merchants and manufacturers are invited to get in touch 

 immediately with the Parade Pageant Bureau. 



COMMITTEE ON STANDARDIZATION OF PHYSICAL TESTS OF 

 RUBBER GOODS APPOINTED. 



J. B. Tutlle, chairman of the Rubber Division of the American 

 Chemical Society, announces the following Committee on the 

 Standardization of Physical Tests of Rubber Goods : 



Professor H. E. Simmons, University of Akron, Akron, Ohio, 

 chairman ; Earl L. Davies, The Goodyear Tire & Rubber Co., 

 Akron, Ohio; W. W. Sanders, Empire Rubber & Tire Co., Tren- 

 ton, New Jersey; Joseph H. Russell, Rubber Regenerating Co., 

 Xaugatuck, Connecticut; Helen C. Gillette, Prest-0-Lite Co., 

 Indianapolis, Indiana. 



NEW YORK TO HAVE LIBERTY LOAN PAGEANT OCTOBER 24. 

 The Publicity Department of the Liberty Loan Committee of 

 New York has established a Parade Pageant Bureau to arrange 

 for a pageant parade under the auspices of the committee on 

 October 24. 



A DETERMINATION OF THE RATE OF SETTLING 

 OF 200-MESH LEAD OXIDE IN RUBBER CEMENTS. 



By S. Albert Kaufman, S.B. 



ALTHOUGH a large percentage of the panicles in 200-mesh 

 lead oxide (litharge) would have a diameter less than 

 the opening of a 200-mcsh screen, which is 0.074 mm., yet by 

 assuming that all the particles have a diameter equal to the 

 opening mentioned above, the worst possibility is taken into con- 

 sideration, consequently working in a factor of safety into the 

 calculations. 



The formula w-hich enables us to calculate the desired result 

 IS the so-called Stokes' formula. 



2R=(S-S')G 



9n 



Where 



V = Settling velocity in cm. per second. 



R = Radius of particle =: 0.037 = mm. 



S = Specific gravity of particle =; 9.39. 



S' = Specific gravity of liquid = 0.74. 



■n = Viscosity coefficient of tlie liquid. 



G= Gravity constant =980. 



Before calculating v, the coefficient of viscosity of the cement 

 was necessary. This was easily obtained by means of the follow- 

 ing formula : 



TrPr* 



81V 



P = Difference in pressure between top and bottom of the tube- 

 rs: radius of the tube. 



1 = length of the tube. 



V = volume per second passing out of the tube. 



7) = coefficient of viscosity. 



The viscosity coefficient for water being known as 0.01, that 

 for our cement could easily be determined by means of a burette 

 and stop-watch, whereby V could be found for both water and 

 the cement. After correcting P for the specific gravities of water 

 and cement, yi for cement was readily determined. 



25 cc. of water passed through the burette in 13 seconds. 



25 cc. of cement passed through the burette in 634 seconds. 

 25 

 V. water = = 1.925 cc. per second. 



