November 1, 1914. | 



THE INDIA RUBBER WORLD 



71 



observing the readings using known mixtures of CO. and air 

 and correcting for the difference in indices of refraction of C0 2 

 and hydrogen or using directly mixtures of hydrogen and air, 

 the former method being easier to apply in the laboratory. 



Tests to determine the variation of diffusion with tempera- 

 ture and pressure show the diffusion rate to vary directly with 

 the temperature within practical limits and to increase with 

 increase in pressure but nol proportionally, increments in per- 

 meability decreasing with increase in pressure. For a given 

 temperature and pressure the permeability increases until the 



In the last quantity the water pressure and temperature vary 

 somewhat with different testing plants. A good spherical balloon 

 fabric obtainable in this country has a weight of TYi, ounces 

 per square yard, strength (one ply on bias) of 40 pounds pi i 

 inch, and a diffusion of 0.4 cubic feet. Two charactei 

 dirigible balloon fabrics have weights of 9 and \A'/> ounces per 

 squan yard respectively, strengths of 90 and 130 pounds per 

 inch, ami diffusion rate of from 0.2 to 0.25 cubic feel I In 

 lirsi is two ply and the other three-ply parallel doubled fabric. 



In addition l" the routine work many research tests have 



1 ■]!.. 4. Apparatus Used n\ the Goodyear Company ro lt-i nn Permeabu I Fabric ro ■ 



fabric becomes saturated with hydrogen, then remains practically 

 constant. 



The units used i:i expressing results of the tests described are: 



I esl Engl Metric. 



Tensile strength Pounds per inch. Kgm. per meter, 



Weight ( lunces pet sq. j d. (lis p( r sq. metei 



Hydrogen diffusion.. .Cubic feet per sip yd. Liters per sq. meter 

 per 24 hours at 2 per 24 hours at 50 

 inches water pres- mm. water pressure 

 sure and 15 i leg (or at 15 deg. C. and 

 sometimes 20 deg. I 760 mm. barometer 

 C. at 29.92 inches 

 barometer. 



bein made, utilizing for the mosl pan apparatus ahead} de- 

 scribed, to determine, for example, the properties . 1 balloon 



fabrics under such special conditions as compound stress, vary- 

 ing weather exposure, extremes of temperature; tin relation "t 

 rate 'it diffusion to temperature and pressure of the gas. the 

 increment .if weigh) due to rain. etc. 



An interesting scries of tisix has been made on the elasticity 

 and ultimate strength of balloon fabrics under compound stress 

 at the National Physical Laboratory in England. The test 

 .specimen was a cylindrical surface of tin- fabric 5 inches diameter 

 by 12 ; j mclics long fitting over metal end pieces so formed that 

 tli surface ami ends a- a whole can lie placed in a testing ma- 

 chinc for the application of a longitudinal tension, while one 

 of the ends connects with an air supply for internal pressure 



Hydrogen Diffusion Apparatus Used in the Chemical Laboratory of the Goodyear Company. 



