Mineral Springs of Colorado. 627 



samples had been acidified and sealed for over a month. 

 Several of the samples were lost during shipment and 

 some were accidentally destroyed where they were stored 

 but it is scarcely to be expected that a greater number of 

 tests would change the general character of the results. 



In the column headed " Remarks' ' the letter S indi- 

 cates results due to Schlundt. 4 The letter a means that 

 the sample has been taken from a pipe or other outlet 

 removed from the source, while b indicates thorium 

 emanation. 



Tests for thorium emanation were made in a great 

 many places where there was a sufficient flow of gas. 

 No indication of thorium was found anywhere except in 

 spring No. 186 in Gunnison Co. near Powderhorn post- 

 office. A roughly quantitative determination, made from 

 the activity curve of the combined radium and thorium 

 emanation and from the activity curve of the radium 

 emanation alone, gave practically the same amount of 

 activity for each. This scarcity of thorium emanation 

 was somewhat unexpected as monazite is found in the 

 sand of most of the creek and river beds so far examined 

 along the whole eastern slope of the Continental Divide. 

 Similar information for the western slope is lacking but 

 the probabilities are that monazite exists there also. 

 Thorium-bearing ores in place are unknown anywhere in 

 the region in which the springs are located. 



For testing the activity of spring deposits in the solid 

 form a sensitive electroscope of the usual type was con- 

 structed. The ionization chamber is a cubical brass box 

 having a volume of one liter. The narrow leaf is 4 cm. 

 long and with its support, insulated by a piece of amber, 

 projects downward into the ionization chamber at the bot- 

 tom of which is a closely fitting drawer for the introduc- 

 tion of the active material. 



The instrument has a measured electrical capacity of 

 1-06 cm. and was standardized by means of thin films 

 of U 3 8 made up according to the method of McCoy 5 but 

 following the specifications of Boltwood. 6 Ten standard 

 films were made from some very pure uranium oxide 

 kindly furnished by Professor Boltwood. In no case did 



4 Jour. Phys. Chem., 18, 662, 1914. 



5 Phil. Mag., 11, 176, 1906; Jour. Amer. Chem. Soc, 27, 391, 1905. 



6 This Journal, 21, 418, 1906. 



