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morter and then thoroughly mixed with alcohol in a tall graduate or glass 
cylinder. The rod supporting the brass disks is next carefully lowered into 
the mixture of alcohol and uranium oxide. The uranium oxide settles to the 
bottom, and in doing so deposits a layer upon each disk, the thickness and 
amount of deposit depending upon the height of the shelf from the bottom. 
Fig. | 
After all the oxide has settled to the bottom the rod is removed and the disks 
allowed to dry. By again weighing the disks the weight of the oxide upon 
each one can be determined. Also by determining the density of the uranium 
oxide the thickness of the films can be calculated. These disks can now be 
mounted upon metal plates for permanent use as ionisation standards, or 
for student use in determining the fact that ionisation currents depend upon 
the thickness of the layer of material up to a certain maximum thickness. 
