250 CHAPTER XX. 



zinc white cement at the bottom, with less than one quarter 

 the tenacity of the caoutchouc cement. 



459. Paraffin. Temporary mounts may be closed with 

 paraffin, or white wax, by applying it with a bent wire, as 

 described 471, and be made more or less permanent by 

 varnishing. 



460. Gelatin Cement. MARSH'S Section-cutting, 2nd ed., 

 p. 104). Take half an ounce of NELSON'S opaque gelatin, 

 soak well in water, melt in the usual way, stir in 3 drops of 

 creasote. It is used warm. 



When the ring of gelatin has become quite set and dry, it 

 may be painted over with a solution of bichromate of potash 

 made by dissolving 10 grains of the salt in an ounce of water. 

 This should be done in daylight, in order to render the gelatin 

 insoluble. The cover may then be finished with BELL'S 

 cement. This process is particularly adapted for glycerin 

 mounts. 



461. The Paper Cell Method. By means of two punches I 

 cut out rings of paper of about a millimetre in breadth, and 

 of about a millimetre smaller in diameter than the cover- 

 glass. Moisten the paper ring with mounting fluid, and 

 centre it on the slide. Fill- the cell thus formed with 

 mounting fluid ; arrange the object in it ; put the cover on ; 

 fill the annular space between the paper and the margin of 

 the cover with glycerin jelly (a turn-table may be useful for 

 this) ; and as soon as the gelatin has set turn a ring of gold- 

 size on it, and when that is quite dry, varnish with BELI/S 

 cement. 



For greater safety, the gelatin may be treated with bich- 

 romate, according to MAKSH'S plan, last . 



462. KOUSSELKT'S Method for Aqueous Mounts (op. cit., 458). 

 Close the mount with a ring of a mixture of two parts 

 of a solution of damar in benzol and one part gold-size. 

 When dry, put on three or four thin coats of pure gold-size 

 at intervals of twenty-four hours, and finish with a ring of 

 WAKD'S brown cement. 



463. WAKI.'S Brown Cement is a shellac-alcohol solution 



