SOME NEW FORMS' OF MOUNTING. 161 



larger than a fine cambric needle would make. With this pro- 

 vision both the cell and the cements go on drying, and there is 

 no sinking in nor moving about of the objects in the cements 

 which hold them. But if the cell be hermetically closed, one 

 may almost certainly expect that the beautiful shell or other 

 object will sooner or later be overwhelmed in a black sea. I* 

 have lost in this way scores of foraminifera and coralline speci- 

 mens on which I had expended a great deal of labor. If curtain 

 rings are used for the cell, a little notch can be filed in the under 

 side of it, and this be left open on the lower side of the slide 

 when finished. 



If the opaque mountings are for dry objects, I make in the 

 center of the ring a disk of Brunswick black, or white zinc, ac- 

 cording as the object to be shown is white or dark. It may be 

 5-16 of an inch in diameter for the Lieberkuhn of the 1^ inch 

 objective, but not over a quarter of an inch for that of the two- 

 thirds objective. After the cement is dry and quite hard, a 

 slight coat of balsam is spread over it, and the objects placed in 

 this and arranged, if necessary, under the microscope. The slide 

 is then set aside to dry, and may be covered safely the next day. 



If the objects to be mounted will bear immersion in balsam, 

 as shells, plant seeds, minerals, etc., I pursue the following plan : 

 The thin glass covers are cemented to some old slips, which are t 

 kept for that purpose, by two or three touches of balsam applied 

 at the edge of the cover. Care is taken in this, and in all cases, 

 to accurately center all work on the slides by means of the self- 

 centering turn-table. Then, on a light coating of balsam in the 

 center of the cover, the objects, whatever they may be, are placed 

 and arranged. When quite dry, and the 'objects are thus securely 

 fastened, they may be completely covered by balsam, and put 

 into the drying oven until thoroughly hardened. Then, over the 

 balsam, Brunswick black, if the objects are white, or white zinc 

 cement, if they are dark or high colored, may be spread, by thin 

 layers at first, each being dried in the open air for a day before 

 the next is applied, until there is an opaque covering to the ob- 

 jects. The thin glass cover is now to be thoroughly cleaned 

 around the objects and then removed from the slip by a slight 



