Long-Period Determination of the Rate of Production of Helium from Radium

In a previous communication the rate of the production of helium from 70 milligrammes of radium chloride was determined by a succession of observations on the growth of pressure measured by a McLeod gauge. These observations extended over a period of about six weeks. It was thought desirable to make an experiment to determine the amount of helium resulting from this same sample of radium, after standing in a sealed bulb for an extended period. For this purpose the bulb containing the radium chloride was sealed off at the conclusion of the above-mentioned experiment of 1908 and kept for nine months. In order to measure the helium thus produced it was necessary to devise a vacuum-tight joint between the sealed radium bulb and a McLeod gauge so constructed that, after thoroughly exhausting the gauge, the drawn-out end of the radium bulb could be broken off, thus allowing the pressure of the accumulated helium in the radium bulb to be rapidly determined. Such a joint is shown in fig. 1. A is the small bottle containing the radium chloride resting in the cylindrical bulb B with long tubular neck drawn out to a capillary, and sealed off at C at the conclusion of the first experiment. This tubular neck slides with slight clearance into the drawn-out neck of another cylindrical bulb D of stout glass, and is attached to it by a short, stout, indiarubber connection protected by a glass mercury cup M, previously fixed as shown on the neck of the radium bulb. This drawn-out neck is so shaped that the radium bulb can be readily rocked in a vertical plane about the neck as pivot within the limits of the diameter of D when so connected.