296 



THE INDIA RUBBER WORLD 



:Makch 1, 1<>19. 



work several specifications were developed providing protection 

 up to 48 hours against the standard test which was in itself 

 much more severe than Tield conditi()ns. N'one of these fabrics 

 was ever used, as the development of gas warfare did not de- 

 mand it. They did, however, represent a reserve for any future 

 developments, thus giving rise to an increase in confidence. These 

 fabrics were, as a rule, made up of rubber but depended for their 

 impermeability upon a film of different material. 



The final specification used coinprised of a No. 4 sail dyed 

 olive drab and coated on one side with rubber to a total weight 

 of 17 ounces. A lighter 11-ounce fabric was used for facing the 

 band of the mask on account of its greater adaptability for 

 yielding a mask with no wrinkles in contact with the face. 



There were two types of compounds used and authorized by 

 the Service, for the reason that various producing companies 

 found them more adaptable. One based 

 upon formulas obtained from the English 

 carried approximately 60 per cent rubber 

 and the balance inorganic filters chiefly 

 composed of China clay and litharge. .\ 

 small amount of mineral rubber and 

 brown substitute was used. The latter was 

 eliminated later. ' This compound lent it- 

 self very satisfactorily to the use of dry- 

 heat cure. 



The other compound, higher in rubber 



per cent), and the balance inorganic 



filler, gave better resistance to gas penetra- 



the roll was cut, the roll was rejected. The manufacturer then 

 had the choice of taking ihe roll back or having it cut at his 

 risk with payment arranged upon a pro rata of acceptable blanks 

 to the whole. 



ELECTRICAL RUBBER FABRIC TESTING MACHINE. 

 W'liilc ihis method did smootli out ihc problem, the Gas De- 

 fense plant (a government-operated assembly plant located at 



Right. 



Long Island City) recognized that many hidden defects might 

 aei liy even the most rigid visual inspection and in turn visual 

 inspection involved the never-constant human element. The 

 plant therefore set about to eliminate this type of inspection and 

 evolved the high-voltage electrical testing machine shown in 

 F'ig'ure 4, which was entirely satisfactory. In this machine the 

 fabric was passed between steel rolls which had an electrical 

 potential difference of 4,000 volts. .\ny hidden hole, thin spots, 

 pit, or embedded metal was broken down ; the current arced 

 through and burned a little circle which was its own rejection 

 mark. 



FABRIC MANUFACTURERS COOPERATE. 



.Mention has liccn made of tlie fact that knots and slugs in 



tile cloth itself were a cause of trouble. This was true because 



tion. It was not found as suitable for the dry-heat cure, how- 

 ever, as the rubber lost much of its life, but to the steain cure 

 this type responded very satisfactorily. 



RIGID FABRIC INSPECTION REQUIRED. 



The early days of fabric manufacture were troublesome times 

 for both the manufacturers and the Gas Defense Service. In 

 the first place only the highest standards prevailed in the 

 minds of the .\rmy representatives and yet in the early days it 

 was not possible to reduce this high ideal to an inspection basis 

 which really eliminated vital defects while allowing those of no 

 consequence to pass. This resulted in the rejection of much 

 material which might have been used, as shown by later ex- 

 perience. Many meetings were held to discuss when a defect 

 was not a defect, etc., without bringing the two interests any 

 closer together. The question of rough spots, the importance 

 of foreign material at the surface and embedded in the fabric, 

 the border linea of pits or depressions, the tremendous effect 

 upon the rubber film of knots and slugs in the cloth itself, all 

 constituted a basis of real difference of opinion which was a 

 matter of great concern. 



Type samples of all kinds of defects representing rejects, 

 border cases, and accepts were finally agreed upon and the 

 basis of inspection reached was a visual inspection of each roll, 

 yard by yard, and a tally of defects. If the number of defects 

 did not permit the plant to get 85 per cent perfect blanks when 



M.ACHiNE FOR Cut 

 Tape. 



STIC Harness 



they became embedded in the rubber and made a thin spot in 

 the film. The early days witnessed strenuous effort to im- 

 prove the cloth used in gas masks. While a very fine cloth had 

 been produced in this country for balloon work, no great 



