12 



THE ART OF MAKING MICROSCOPE SLIDES 



Cells 



will therefore be described. Cement cells 

 are made with a turntable in the manner 

 shown in Fig. 7. Turntables are of many- 

 patterns but consist essentially of a rest 

 for the hand and of a rotating circular 

 plate bearing chps to hold the slide. These 

 plates have the center marked, usually 

 with a series of concentric rings engraved 

 round it. The center of the shde must 

 first be marked, and this is readily done 

 by placing the slide on a sheet of paper, 

 running a pencil around its edges, and 

 then drawing the diagonals of the rec- 

 tangle so formed. The shde is replaced on 

 the rectangle and a dot made with India 

 ink at the point immediately above the 

 intersection of the diagonals. The shde is 

 transferred to the circular plate of the 

 turntable with the dot over the central 

 point of the plate. The cement ring should 

 be of the same diameter as the covershp 

 and one of the circles on the plate may be 

 used as a guide; if there are no guide hues, 

 a ring should be marked on the underside 

 of the slide of the same diameter as the 

 covershp to be used. The brush is charged 

 with the cement and the table spun quite 

 rapidly by means of the milled ring shown 

 in Fig. 7. It is safer to use this milled ring 

 than to use the edge of the turntable be- 

 cause the shde frequently projects slightly 

 beyond the edge and may be tapped off 

 center with the finger used for spinning. 

 The charged brush is brought slowly down 

 over the marked ring and held in contact 

 with the spinning shde so that a circle of 

 cement is drawn on the glass face. Re- 

 member that you are not painting a thin 

 ring of varnish on the slide; you are en- 

 deavoring to build up a relatively thick 

 layer of cement by allowing it to flow from 

 the brush to the shde. The hairs of the 

 brush should never touch the glass itself ; 

 only the cement should touch the glass 

 and thus be drawn off. In making a dry 

 wholemount it is not very important how 

 wide the ring is, but a %6-inch-wide ring 

 for a %-inch covershp will be about cor- 

 rect. As many shdes as are likely to be 

 required are prepared at one time and may 

 be left to dry indefinitely. Cells prepared 

 with an ordinary sample of good gold size 

 are safe to use after about 24 hrs. Building 

 up a thick ring of cement by the applica- 



tion of successive coats is rarely satisfac- 

 tory. A gold-size ring prepared in the 

 manner described will have a thickness 

 between one- and three-thousandths of an 

 inch. If thicker rings are required, it is 

 better to use cells made of paper, card- 

 board, tin, or plastic. 



Paper rings are stamped from a sheet of 

 the required thickness (a good quality 

 bond paper runs from three- to five-thou- 

 sandths of an inch) or from Bristol board 

 (6- to 12-thousandths of an inch) or from 

 cardboard (up to a thickness of about Ke 

 of an inch). The best board to use is the 

 dense black bookbinder's board (once 

 known as millboard) since cheap yellow 

 strawboards have such a rough surface 

 that they can be made to adhere only 

 with difficulty to a glass slide. SheUac is a 

 good adhesive for attaching paper, or 

 thin card, to a glass slide. A sheet of bond 

 paper is coated on one side with com- 

 mercial sheUac varnish and then dried. 

 Rings of the appropriate size are stamped 

 from this shellac-coated sheet, either by 

 using two punches successively, or with a 

 double punch. The outer diameter of the 

 cell should be larger than that of the 

 covershp, while the inner diameter should 

 be less, so that when the cover is laid in 

 place there wiU be an appreciable overlap 

 of paper both inside a-nd outside. A large 

 number of these stamped rings may be 

 cut at one time. When required for use, 

 one is centered on the shde and then 

 pressed into place with a hot iron, raised 

 to a temperature which will melt the 

 sheUac. When the shde has cooled, it is 

 turned upside down and observed with 

 light reflected from it at an angle. If the 

 cell is perfectly attached no adjustment 

 of the angle of observation will produce 

 mirrorhke reflections from the underside 

 of the cell; if any considerable area of the 

 underside of the cell shows mirrorhke re- 

 flections, it is not properly attached and 

 had better be rejected. Cardboard cells 

 more than He of an inch thick are not 

 satisfactory, for they are so porous that 

 they admit moisture in humid weather and 

 allow fungus growth on the specimen. The 

 outside of the ceh may, of course, be 

 covered with some waterproof cement, but 

 this makes a clumsy looking mount and it 



