[elworthy-murray] balloon FABRICS 39 



Description of Apparatus 



The general arrangement of apparatus is shown diagrammatically 

 in Fig. 1. 



(a) The Air Circuit 



The air stream maintained by means of a water pump and kept 

 at a constant pressure by a blow-off, passed {i) through a flow meter 

 which served to check the uniformity of the rate of flow, {ii) through 

 a gas meter which measured the volume of air, {Hi) through a drying 

 train of calcium chloride and of sulphuric acid {iv) through a copper 

 coil in a thermostat which ensured that the air was at the temperature 

 of the fabric and then {v) through the air chamber of the permeameter. 

 The outgoing air containing hydrogen or helium which had leaked 

 through the fabric then passed (i) through a coil at air temperature, 

 {ii) through a drying tube and then {Hi) through a Jamin Inter- 

 ferometer or out into the air as desired. 



{b) The Gas Circuit 



The gas, helium or hydrogen, passed (i) through calcium chloride 

 tubes and a sulphuric acid wash bottle, {ii) through a Shakespear 

 Hydrogen Purity meter which indicated the purity, {Hi) through a 

 coil in the thermostat, {iv) through the upper chamber of the per- 

 meameter, {v) through calcium chloride and phosphorus pentoxide 

 drying-tubes, {vi) through a chamber communicating with a Katharo- 

 meter which indicated the purity of the gas and {vii) through a wash- 

 bottle which served as a pressure regulator {viii) to the gas-outlet. 



(c) The Permeameter 



The permeameter, made to the design of Dr. G. A. Shakespear, 

 was supplied by the Cambridge Scientific Instrument Co. Plate I 

 shows the exterior with the Katharometer in position. It consists 

 of two shallow circular drums, each about 26 cms. diameter and 1 cm. 

 depth, with machined flanges 1-6 cms. wide. The volume of the air 

 chamber is 500 cc. As will be seen from Plate II, the fabric is sup- 

 ported by concentric rings of metal which are notched so as to obtain 

 uniform diffusion of gas or air throughout the chamber. 



Conditions of Testing 



As permeability is dependent upon a number of factors, the 

 conditions under which the tests in this paper were carried out are 

 stated under the following headings: 



