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THE INDIA RUBBER WORLD 



Skitembek 1, 1921 



with and used this test for a matter of twelve years, and it has 

 so often demonstrated its value that this International Rubber 

 Conference is a most fitting place to tell of its practical value. 



Let me now briefly review in conclusion the lessons that we 

 feel have been learned during these years. 



(1) We consider it more reliable to plot the curves and com- 

 pare them than to consider the percentage deterioration from the 

 original tensile strength. 



(2) The samples are not hardened as in actual aging, but 

 are definitely weakened. 



(3) Sulphur changes are noticeable, but not important. 



(4) The test is of little or no value when used upon com- 

 positions of which the tensile strengths are undor about one 

 thousand pounds per square inch. 



(5) Despite the fact that the curves of short and natural- 

 life tests do not exactly parallel, the short-life test is somewhat 

 more severe in general than the natural life. 



(6) Most important. We are convinced that in the vast 

 majority of cases too rapid deterioration of rubber compounds 

 is due to over or undercure, and chiefly overcure, rather than 

 to any one or more compounding ingredients. This life test 

 with us has been of utmost value in leading us to correctness of 

 cure. Our troubles with organic accelerators, various grades of 

 unfamiliar crude rubber, mineral fillers of various kinds, and so 

 on, have been due chiefly to our attempts to graft a lu-w mate- 

 rial upon an old practice and often with fatal results. 



(7) This test is a comparative and not an absolute one and 

 should never be used to compare compounds of different type. 



(8) When used properly, there has been found to be an ap- 

 proximate correspondence between short-life and natural-life test, 

 after four days in the oven, of one short day equalling si.x months. 



RUBBER HOSE IN DUST-SPRAYING 



As an accessory of vacuum cleaners, rubber hose has been long 

 and efficiently employed in removing dust, but it has remained 

 for agriculturists to utilize hose in blowing dust upon growing 

 plants to save them from the ravages of insects and give them 

 a more salable appearance. 



The dust is usually a powder containing a large proportion 

 of nicotine, pulverized dry-lime sulphur, or a pure tobacco dust; 

 and aphis, thrips, slugs, codling-moth, and other orchard and 

 garden pests are readily destroyed with such dry-spraying. The 

 average cost of dust and applying to a full-grown walnut tree 





.^'■-^j^i.^^ 



Dust Sprayer Dr.\\vn on Skids Between Rows 



is ASYz cents. For this work the largest size of power dusting- 

 machine is used, and a 4-inch hose, 20 feet long, is employed. 

 The workers prefer light, rubber, cotton-jccketed hose. 



For light truck gardening, hand-dusters — with the powder 

 under pressure — to which are attached 1-inch rubber canvas- 

 covered hose, are much used; but for large ranches a duster 

 operated with gasoline power and mounted on a truck is gen- 

 erally preferred. A small power outfit uses either one 3-inch 

 rubber hose or two of l54-inch diameter each. Better dust dis- 

 tribution is effected, it is claimed, with the two separate and 

 smaller lines of hose than with the single and larger hose. So, 

 too, the work can thus be done in a shorter time, which means 

 much in checking infestation. 



