Abstract
In the ethylene glycol method of grading collodion membranes 1 the grading is brought about not, as Pierce supposed, by ethylene glycol alone but by ethylene glycol plus the alcohol retained in the membranes after 24 hours drying.
Ethyl alcohol is readily absorbed both by ethylene glycol and by calcium chloride, therefore the amount of alcohol retained by the membrane is determined in part by the per cent of glycol in the collodion solution employed, and in part by (1) the quality of calcium chloride used in the outlet from the drying chamber and (2) the accessibility of this chloride to the alcohol vapors from the chamber. By varying the diameter of the opening between the floor of the drying chamber and the container of calcium chloride, wide variations were produced in the “weight before washing” and in the “wet weight” of membranes prepared from collodion solution of the same ethylene glycol content, while with the calcium chloride constant in all respects the grading by means of ethylene glycol was good.
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