Cements 



DRY WHOLEMOUNTS 



15 



cell. If you are using an optical-dead-black 

 based on gold size, clear gold size itself is 

 th*e best cement. A series of fine drops of 

 gold size are placed in the positions which 

 the objects are subsequently to occupy, 

 and the objects added one after another. 

 This will result in perfect adhesion, but 

 the sUde will have to be left uncovered 

 and flat for at least two or three days, to 

 harden the gold size before the cover is 

 attached. When using an optical-dead- 



at a relatively high temperature and all 

 too often this high temperature causes the 

 dead-black cement to break away from 

 the glass. When using these cements, a 

 piece about one third of the size of the 

 object which it is desired to attach is 

 broken from the mass. These pieces of 

 cement are placed on the bottom of the 

 cell in the positions which the objects will 

 occupy and the slide placed on a hot table 

 to melt the cement. The author prefers 



Fig. 8. Using a warm table to attach cells with marine glue. 



black cement secured from a scientific 

 supply house, it is necessary to secure 

 some of the varnish medium in which the 

 black has been suspended. The writer has 

 seen hundreds of commercially prepared 

 strewn sHdes of Radiolaria and Forami- 

 nifera in which gum arable had obviously 

 been used on black varnish backgrounds 

 and in which from a third to a half of all 

 the specimens were loose. As a second 

 choice to the varnishes, there may be em- 

 ployed one of the Canada-balsam-resin 

 cements of the type of Fant 1932 (Chapter 

 28, V 12.2), or one of the Venice-turpen- 

 tine cements of the type of Gage 1896. Un- 

 fortunately these cements have to be used 



the type of table shown in Fig. 8 which 

 consists of a strip of heavy metal, prefer- 

 ably copper, bent back twice on itself and 

 mounted on four legs. The top of the 

 upper strip projects beyond the bent por- 

 tions. A burner is placed under this pro- 

 jection and adjusted to keep the end of 

 the strip well above the boiUng point of 

 water. It will be seen that the temperature 

 steadily diminishes from shelf to shelf, 

 that of the upper shelf being highest, that 

 of the second shelf being lower, while the 

 bottom shelf is scarcely warm. To deter- 

 mine whereabouts on the shelf to place the 

 slide it is only necessary to place a few 

 chips of cement at about one-inch inter- 



