Table of contents

The apparatus determines the moisture content of the air directly in terms of the aqueous vapour pressure thereof. It is a modification of the chemical hygrometer. An air sample of fixed volume is exposed to a chemical drying agent and the consequent reduction in pressure observed. This is proportional to the vapour pressure originally in the sample. Convenience in operation, rather than high accuracy, is claimed for the device.

A form of apparatus for the production of high-class silver mirrors by cathodic sputtering is described. Several essential precautions are stated, and the conditions necessary for the production of such mirrors are discussed.

The addition of a magnetizing winding to a differential transformer simplifies measurements and increases their precision. The theory of a simple method of measuring inductance with such a transformer is described and is illustrated by an experimental result.

A method of determining the relative intensities of two spectral lines of nearly the same wave-length is described. It is based on the use of a "stepped wedge" made by depositing platinum on fused silica. Microphotometric readings are taken of the density of two consecutive steps on one line of the pair, and a similar reading on a step of intermediate density on the other. An expression is derived from which the relative intensities of the lines can then be calculated. Tests show that the accuracy of the method is such that the probable error of a single determination is about 1½ per cent. Preliminary results of an application of the method to the quantitative analysis of lead in tin are given. Certain conclusions of general interest in spectrum analysis are drawn; they concern the effects of background in the spectrum, and the regularity of light emission from sparks run on the conventional circuit.

In the usual method of mechanical analysis of finely divided solids, the specimen is allowed to sink in water, and measurements are made of the concentration or density at various depths after fixed times. In the present apparatus, which is designed for particles whose diameter lies between 1 and 12μ, the "sampling" is done by means of a beam of light and photo-electric cell. Examples of the application of the apparatus are given.