The Radio Activity of the Karapiti Blowhole.

By M. N. Rogers, M.Sc.
(Communicated by Dr. C. C. Farr, F.N.Z. Inst.)

[Read, before the Philosophical Institute of Canterbury, 2nd December, 1925; received by Editor, 8th December, 1925; issued separately, 8th March, 1927.]

The following examination of the Radon-content of the gases from the Karapiti Blowhole was made to confirm a result which the writer and Mr. F. J. T. Grigg, M.Sc., obtained in 1921.

The Blowhole is situated about three miles north of Taupo, and emits a large quantity of steam (mixed with other gases) at a considerable velocity. Two small cans of the gas were collected over water and kindly forwarded by Dr. C. C. Farr from Taupo, and were examined immediately on arrival in the Physics Laboratory, three days after collection.

The gases were removed from the cans into an evacuated electroscope which was connected by rubber tubing to a brass tube soldered to the top of the can. Water was allowed to enter through a small hole in the bottom of the can, the increase in weight of the can thus giving the volume of gas placed in the electroscope. The gases were carefully dried by bubbling slowly through concentrated sulphuric acid.

The electroscope consisted of a brass box containing a sulphur insulated gold leaf. The leak obtained with the gas was more than one thousand times the natural leak, which could, therefore, be neglected, but continued observations of the natural leak were made throughout the examination. The constant of the electroscope was one scale division per minute for 45 × 10^-12 grms. of Radium.

Five separate quantities of the gases were placed in the electroscope, and the maximum variation was not more than 15% from the mean.

The Radon-content of the gases per cubic centimetre was found to be that quantity which would be in equilibrium with 8.4 × 10^-12 grams of Radium. This is in fair agreement with the value (as yet unpublished) of 6.0 × 10^-12 obtained on the previous occasion. The difference in the values is most likely due to the different method of standardization as, in the former case, the emanation was liberated from pitchblende of known composition by fusion at 1,000 degrees C., while, in the latter, a solution of the emanation was employed.

The rate of fall of the leaf was found to rise over a period of four hours from 3.8 to 5.2 divisions per minute, confirming the conclusion that the ionization was due to Radium-emanation.