SHUDDEMAGEN. — RESIDUAL CHARGES IN DIELECTRICS. 513 



will prevent them from sticking to each other. As soon as the two 

 sheets have been removed from the board and laid away, the dipping 

 board is again flushed with cold water and the process is repeated. 



The reason for having the dipping boards bevelled sharp at the side 

 and bottom edges is that this causes a break in the paraffin layer there, 

 and so allows the two sheets to be peeled off separately. The reason 

 for having more than one dipping board is that one is liable to give 

 poor results ; for the paraffin may begin to stick to its surface, and 

 when it once starts to do so, the trouble is hard to correct in any other 

 way than by letting the board get dry once more and vigorously sand- 

 papering the troublesome place. Using two or three boards, one may 

 pick out after trial the one which gives the best sheets. 



By varying the conditions somewhat, one may obtain smooth paraffin 

 sheets of almost any thinness desired. They are very easily, and per- 

 haps most conveniently, made about half a millimeter thick. If the 

 water bath is made hotter, the sheets of paraffin will turn out thinner, 

 until finally there comes a time when the paraffin film will split and 

 full-size sheets cannot be obtained. Another means of controlling re- 

 sults is found in the temperature of the wet dipping board. The 

 warmer it is allowed to become the thinner will be the sheets. With 

 a little practice and judgment one can get sheets of good, smooth sur- 

 face. A good deal depends on keeping the surface of the melted paraf- 

 fin in the smaller tank free from air bubbles. Usually the sheets ob- 

 tained will be thinner near the top end of the dipping board and thicker 

 near the lower end, but this makes little difference if one cuts con- 

 denser sheets out of the middle portion. 



About two hundred good sheets were made by the writer in a few 

 hours one afternoon, of the grade of paraffin melting at 47°. 5. The 

 water adhering to these sheets was allowed to evaporate over night by 

 laying the paraffin sheets singly on large sheets of rough paper, such as 

 is used for mimeograph work. The water in evaporating is likely to 

 leave a conducting film over the paraffin, and moreover there are some 

 slight unevennesses in the surfaces of sheets. It was found that the 

 thin blades of steel used in the Gillette safety razor were admirably 

 adapted for use in lightly scraping the paraffin, and in this way the 

 conducting films were removed and very smooth sheets resulted. For 

 this operation, and in fact to be handled at all, the paraffin should be 

 kept in a room at a temperature of about 23° or 25°. The sheets are 

 then sufficiently yielding and plastic, so that they may be scraped 

 without danger of cracking. 



When a sheet had been thus scraped smooth, it was immediately 

 used to build up the condenser. 1 A smoothly scraped surface of a sheet 



VOL. XLIV. — 33 



