Dr. D.C. Bardwell, of the Research Lab. of the U.S. Bureau of Mines, collecting gaseous radium emanation. The radium is in the little safe at the right. Collections are made at intervals of from 4 to 10 days. The gas is drawn off under vacuum and purified by a liquid air refrigeration. The purified gas, very small in volume but powerful in its action is used in the study of gas reactions. The work is under the direct supervision of Dr. S.C. Lind, chief chemist of ther Bureau of Mines