512 PROCEEDINGS OF THE AMERICAN ACADEMY. 



which just reached over the top rim of the outer tank, and held the 

 inner one at such a height that its top was about 1.8 cms. higher than 

 the top of the larger tank. This was done to keep the water from 

 getting from the outer tank into the inner one. 



Meanwhile two " dipping boards " were obtained. These were made 

 of light pine (whitewood may be better) and are 61 cms. long, 25 cms. 

 wide, and about 0.5 cms. thick. They are bevelled down to a narrow 

 V'-shape along both of the long edges and one end. Near the other 

 end a hole is bored through, so that each board can be hung from a 

 hook. These boards are carefully planed, and then sand-papered until 

 they have a very smooth surface and are free from loose fibres of wood. 



A day or two before the paraffin sheets are to be " dipped," the two 

 dipping boards are wholly immersed in water and left there until 

 needed. Before this immersion strips of wood should be tied across 

 the boards so as to keep them from warping when they become thor- 

 oughly water-soaked. This must also be done after the work of mak- 

 ing the paraffin sheets is finished, and the boards are to be allowed to 

 dry ; otherwise they will surely warp in drying. When the boards 

 have become thoroughly water-soaked, the paraffin is melted in some 

 convenient large vessel, placed in another one containing water to 

 which the heat is applied ; meanwhile the larger tank is filled about 

 half full of water, and this is heated by Bunsen burners placed under 

 the tank. Before the water has reached its boiling point the burners 

 are taken away or turned down very low, then the smaller tank is 

 placed in the larger one and the melted paraffin is filtered into it 

 through some clean piece of cloth, preferably linen. The smaller tank 

 is filled to such a depth with paraffin that, when one of the dipping 

 boards is lowered all the way down into it, the paraffin will rise nearly 

 to the top of the tank but not run over. Now one of the dipping 

 boards is flushed with water under a faucet, and when this has been al- 

 lowed to drain off until the water falls by drops, the board is quickly 

 pushed down into the paraffin and as quickly withdrawn, being held at one 

 end by both hands. This will result in a thin layer of paraffin quickly 

 cooling all over the two sides of the board, and if the conditions are 

 just right very little paraffin will drip from it. When after about a 

 minute the surface of the paraffin has become firm, cold water is again 

 flushed all over the board, but only for a very short time. This makes 

 the paraffin layer so firm that the board can be hung from a hook and 

 the paraffin peeled off in two layers. These sheets, about 25 by 52 

 cms., are piled up one on top of the other on flat board, just as they are 

 peeled off the dipping board, and can usually be left in that way for a 

 day or two in a moderately cool room, since the water still on the sheets 



