Mineral Springs of Colorado. 633 



these films weigh as much as 5 mgs. and the material was 

 spread uniformly on thin sheet aluminium over a surface 

 of 64 sq. cm. The ten films gave an average activity per 

 milligram of three divisions per minute. One division 

 per minute corresponds to 2-82 X 10 -4 gram uranium. 



Dry samples of the materials to be examined, weighing 

 roughly from 0-5 lb. to 3 lbs., were first pulverized so as 

 to pass through a 100-mesh screen. Small portions of 

 these were further ground with freshly distilled chloro- 

 form in an agate mortar and this material was thinly 

 painted with a camel's hair brush over sheet aluminium 

 of the same area as the standard films. These films 

 were made much thicker, however, than the standards so 

 that considerable absorption undoubtedly occurred for 

 which no correction has been made. 



The activities of the deposits, muds or sediments from 

 a number of the springs listed in Table I are given in 

 Table II. It was not possible to collect such samples 

 from all the springs. The samples taken were usually 

 from springs which showed at least some activity in the 

 water or gas. From some springs more than one sample 

 was taken when the deposits appeared to differ in nature, 

 color, or age. These are indicated in the table by a repe- 

 tition of the spring number. 



In the column headed "material" will be found a classi- 

 fication made by the Colorado State Geological Survey 

 but no formal analysis has been attempted. Column 3 

 expresses the activity as equivalent to that of so many 

 grams of uranium per gram. Up to the present it has 

 not been possible to do the work necessary to determine 

 the exact substances to which this activity is due. Small 

 portions only, even of what appeared to be calcareous 

 deposits, were soluble in acids. The deposits contain 

 large amounts of clay and silica and the radioactive salts 

 occur generally in the form of sulphates. 



The values given in column 4 were obtained by the 

 method of. fusion with mixed carbonates. The samples 

 were sealed for over a month in combustion tubing and 

 care was taken to avoid loss of emanation during fusion. 

 Column 5 contains a few results obtained by the boiling- 

 out method from complete solutions of a few grams of 

 material. This of course is the ideal method for reliable 

 results. However, aside from the fact that lack of time 

 has prevented the use of this method in all cases, it is 



