622 Lester — Radioactive Properties of the 



nearest railroad it was decided to do all traveling by- 

 automobile. A large box divided into convenient trays 

 and compartments was built firmly into the back part of 

 the machine. This held all the necessary apparatus and 

 supplies for a well-equipped field laboratory and made it 

 possible to use the more accurate boiling-out method 

 described by Boltwood 1 instead of the Fontaktometer. 

 Mr. J. H. V. Finney, an instructor in the department of 

 Physics of the University of Colorado and a skilled auto- 

 mobile driver and mechanic, acted as general assistant 

 not only in the field work but also in the tests made later 

 in the laboratory. "Without his efficient services the work 

 would not have gone so smoothly nor could so much have 

 been accomplished in the comparatively brief time of one 

 summer. 



The general plan of the work was to visit each spring 

 and to make tests on the spot for the immediate activity 

 of both water and gas. By immediate activity is meant 

 the activity of freshly collected samples. "Wherever it 

 was possible the gases were also tested for thorium 

 emanation. Samples of water and mud or sinter (if 

 any) were collected chiefly from springs showing fair to 

 high activity and shipped to the laboratory at the Uni- 

 versity to be tested later for dissolved or deposited radio- 

 active substances. 



The field tests occupied the whole of the summer of 

 1914. A few short trips were made in the fall of 1914 and 

 in the summer of 1915. Tests for activity due to salts 

 dissolved in the waters or deposited in muds and sinters 

 continued at various times during the winter of 1914, 

 most of the summer of 1915, and for some time in 1916. 

 During this time tests were made also on the immediate 

 activity of waters shipped in from a number of springs 

 not examined during the work in the field for reasons 

 given above. 



To avoid loss of time in waiting for an electroscope 

 contaminated by active deposit to become usable again, 

 several instruments or their equivalent were necessary. 

 On the other hand our carrying capacity though large was 

 not unlimited nor did we wish to have the care of packing, 

 repacking and of keeping in order a number of pieces of 

 apparatus as delicate as the leaf system of an electro- 



1 This Journal, 18, 378, 1904. 



