222 E. D. EVENS ON 



for sealing museum jars, and it occurred to me that this might be 

 a suitable material for microscopic purposes. 



On trying it, however, it was found unsatisfactory, as in a 

 short time after manufacture it changed in some way, causing 

 it to char and not melt when heated. It was then suggested 

 that unvulcanised raw rubber should be tried, and this was 

 found very satisfactory. 



Best Para " Bottle " rubber is cut into small pieces and added 

 to eight times its weight of paraffin wax (m.p. about 50° C.) and 

 melted in a water-bath. It is kept at 100° C. until the whole of 

 the wax has been absorbed by the rubber, which by this time will 

 have swollen up enormously ; the time required is from 12 to 24 

 hours. The temperature should then be raised to about 175° C. 

 or until the mixture just begins to smoke. In about thirty 

 minutes it will gradually melt down to a clear liquid. Four 

 and a half parts of dry dammar resin are now stirred in and 

 the whole thoroughly mixed. The gum dammar hardens the 

 cement when cold and makes it more fluid when hot. 



Paraffin wax (m.p. 50° C.) , . . .8 parts 

 Para (" Bottle ") rubber . . . .1 part 

 Gum dammar ...... 4| parts 



I call this mixture, from the initial letters of its components, 

 D.I.P. cement. 



The bulk of this is composed of paraffin wax, and, since the 

 solubility of water in it is very small, it should make a much 

 more satisfactory first coat than, say, gold-size ; and, in fact, 

 a layer melted on to glass is very much less affected by water 

 than any other known cement. Pure paraffin wax floats off 

 after immersion in water for a few hours. 



In order to make a cell of this D.I.P. mixture some of it is melted 

 in a tin, getting it as hot as possible without allowing it to smoke. 

 A clean glass slip is then heated over a spirit lamp, placed on the 

 turntable, and a ring of the cement spun as quickly as possible on 

 it. If the temperatures have been arranged properly this ring will 

 remain melted on the slip for a few seconds and will then solidify. 

 Further rings may now be added till the cell is deep enough. 



After cooling completely the cell should be turned down to a 

 smooth upper surface, and to the required depth, using a sharp 

 knife and spinning the table rapidly just as if one were turning 



