Discovery of Radon

obta.ined from a platinum-wire katharometer is weaker than that from a thermistor device, but can

be applied to a spot galvanometer or a recording potentiometer of 1 m V. span, without pre-amplification. The columns and katharometer are immersed in an oil-bath which is maintained at 30 ± 0 •05° C. It has been claimed• that if the current flowing through the bridge circuit is kept constant, the response obtained from the katharometer is independent of temperature. While this appears to be true for certain gases, of which hydrogen is one, in practice it has been found to be very difficult to mainta.in the current within the necessary limits, as a small error in setting the current produces a magnified error in the response. In order to obta.in a high degree of reproducibility, the alternative procedure of maintaining the apparatus at a constant temperature has been adopted.

Oxygen-free nitrogen is normally used as the carrier and reference gas. In cases where a particularly high sensitivity is required, it has been found advantageous to use argon for this purpose on account of its lower thermal conductivity. The pressure drop across the columns is maintained at 14 cm. of mercury, this being equivalent to a flow-rate of about 50 ml./ min. through each column. A 10-ml. sample is taken for each analysis, hydrogen being eluted from the separating column after 40 sec. For gases which are eluted from the column very rapidly, it is permissible to assume that the peak height is proportional to the amount of the component present, over a wide range of concentrations ; thus the recorder can be calibrated directly in terms of hydrogen. Determinations can be carried out with an accuracy better than ± 0 •005 per cent of hydrogen, and amounts down to O •005 per cent can be detected.

This instrument was primarily designed for the determination of hydrogen, but methane can also be determined, being eluted from the separating column in 2 min. 30 sec. As would be expected from the lower thermal conductivity of methane, the sensitivity of the instrument to this gas is rather lower than in the case of hydrogen. For methane, the precision and sensitivity are rather less than that obtainable with the Haldane apparatus ; but the extreme rapidity of gas chromatography makes the method useful when the saving of time is an important consideration.

P. WHATMOUGH Scientific Department, Central Laboratory, North Western Division, National Coal Board, Shade House, Bolton Road, Pendlebury, Manchester.

1 Janak, J., Chem. Listy, 41 (6), 828 (1953) . 'Janak, J., Chem. Listy, 41 (6), 837 (1953) .

• Ambrose, D., and Collerson, R. R., J. Sci. Instr., 32, 323 (1955) .

• Percival, W., Analyt. Chem., 29 (1), 20 (1957) .