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232 patch from the repair-box, of small size if the puncture be a mere perforation, but larger if the tube be cut. Clean the tube round the hole with glass-paper or petrol, brush dry, and then apply solution, over a space somewhat larger than the patch. Next cover the patch with solution also, on the side that is not bevelled. In each case the solution should be thinly and evenly spread, not in clots. Wait until all traces of moisture have disappeared—a point of paramount importance and then fix the patch upon the tube, pressing the surfaces firmly together. There should be no ambiguity about the adhesion; the patch will stick like a leech at once if the solution has been thinly applied and sufficient time—from five to ten minutes— allowed for it to dry.

To Repair the Cover.—Before replacing either a new or repaired tube the cover should be attended to. If the hole or cut be very small, it will suffice to plug it with cotton wadding, soaked in solution, to prevent the ingress of water or dirt; the possibility of the air-chamber, however, under strong inflation, forcing its way into the aperture and bursting must be borne in mind, and when doubt exists as to the safe course to follow an oblong patch of canvas should be applied instead. The lining of the cover should be cleaned with glass-paper and solution spread on the fabric and on the canvas patch, as described above in the case of the air-tube. Apply a liberal dose of powdered chalk to the patch when fixed.

Replacing the Tube.—Considerable care is requisite when inserting an air-chamber. It should first be plentifully chalked, and a handful of chalk should also be placed in the well of the cover, and distributed by revolving the wheel two or three times. The opposing surfaces are thus well lubricated, and the possibility reduced to a minimum of nipping the tube, a factor which M. Michelin has declared to be the cause of fifty-one per cent of the injuries to air-chambers. Ensure that the tube is entirely deflated before replacing; to effect this it must be rolled upon itself and all the air squeezed forwards towards the valve, all the parts of which