Bursting pressure=80 lbs. per square inch. Bursting pressure = 109 lbs. per square inch. Summing up the preceding results, they are arranged in the following Table:— SECTION IV. ON THE RESISTANCE OF GLASS GLOBES AND CYLINDERS TO AN EXTERNAL PRESSURE. The following experiments are in continuation of, and supplementary to, the researches on the collapse of wroughtiron vessels already alluded to. In this aspect they are the most important in their bearings and the most novel of any in the present memoir. The method of conducting them did not differ in any essential detail from that pursued in the researches upon wrought-iron tubes, described in a former paper. A number of globes of varying dimensions were procured, and hermetically sealed by means of the blowpipe. In this state they were fixed in the interior of the strong wrought-iron boiler B (fig. 10) (capable of sustaining a pressure of about 2500 lbs. per square inch), in the posi tion shown at A. The boiler or vessel B communicated, by means of the pipe a, with a hydraulic force-pump having a plunger of three-quarters of an inch diameter, so that a uniform pressure of about 1000 lbs. per square could easily be obtained. In order to register the pressure, gauges of the Schaeffer construction* (C) were employed, as before, affording, within small limits of error, certain and accurate indications of the increase of pressure obtained by the pump. The collapse of the glass vessel was made known by a loud report, and by the instant recession of the moveable finger of the gauge i; the maximum pressure obtained was marked by a second finger k, and also, to prevent error from any accidental cause, by the eye of the observer. inch * In pressure-gauges of the Schaeffer construction a corrugated steel plate measures the force, by expanding under pressure. The indications are communicated by a rack and pinion to the hand of the gauge which moves over a face plate graduated by trial. In principle this gauge does not materially differ from the aneroid barometer. During the collapse the globes were reduced to the smallest fragments; in some cases a great part almost to powder, by the violence of the concussion. Hence in ese experiments no indication could be found of the ode in which the globes had given way, nor of the rection of the primary lines of fracture. 76 ON THE MECHANICAL PROPERTIES OF GLASS, After the globe had been ruptured, the fragments were carefully collected, and a selection having been made of the thinnest, they were measured, as before, by means of a micrometer-screw. The minimum thickness thus determined has been assumed for the thickness of the point of rupture in the calculations. |