India Rubber

Some few years ago Lientenant Yladimii'off of the Russian navy made a series of experimeuts to establish the testing of rubber goods on a sound and satisfactory basis, the following being the main conclusions at which he arrived. It will be seen that the tests advocated are physical ones, as he carne to the conclusión that cheiuical teating gave no reliable results. First. - India rubber should not give the slightest sign of superficial cracks on being bent to au angle of 180 degrees after five hours' exposure in a closed air bath to a tempera ture of 125 degrees C. The test pieces should be about 6 centimeters thick. Second. - Rubber containing not more than 50 per cent by weight of metallic oxides should stretch to five times its length without breaking. Third. - Pure caoutchouc f ree from all foreign matter, except the sulphur necessary for its vulcanization, should stretch seven times its length without breakiug. Fourth. - The extensión measured immediately after rupture should not exceed 12 per cent of the original length of the test piece. The test pieces should be from 3 to 12 millimeters wide, and not more than 0 millimeters thick and 3 centimeters long. Fifth. - The percentage of ash gives a certain indication of the degree of softness, and may form a basis for the choice between. different qualities for certain purposes. Any excesses of sulphur over that required for vulcanizatiou should be removed at the works, and should not appear on the surface of any object. Now, these tests on the whole seem very well calculated to give useful indication to engineers as 'to the quality of the goods they are buying, only we would interpólate here the reinark that unless a good price is paid for the rubber it is no use submitting it to such physical tests as these. India rubber substirutes made from oil and "recovered rubbers" - that is, old rubber worked up again with oil - have nothing like the elasticity appertaining to new, sound rubber, and they are quite incapable oí standing the elongation or heat test nientioued. ■