228 DAVID BRYCE ON THE 



trough. For the framework take an oblong piece of sheet-rubber 

 5J inches x IJ inch, and J inch thick. Cut this lengthwise 

 into three slips J inch wide. Two of these will form the sides, 

 and the 3-inch bottom is cut from the third, leaving a length 

 of 2J inches to be cut again for a loosely fitting " cork " (fig. 1, b). 

 For back and front provide two pieces of thin plate glass 6 inches 

 X 3. To one of these cement the bottom slip of rubber and 

 the two slips for the sides, making good joints between. After 

 they are set hard, fix the other glass in position. I find in prac- 

 tice that troughs built up of three pieces of rubber cemented 

 together last quite as well as those wherein the rubber frame 

 is of one piece, as originally specified for this " bottle." The 

 various dimensions and the thickness of the rubber can be varied, 

 but those stated make a convenient and useful size. When 

 cutting rubber the knife should be kept wet. 



The stage troughs (fig. 1, c) are made in a similar way, but from 

 rubber J inch thick. The front and back are of thinnest plate 

 glass 2 X 2J inches. The rubber is cut into strips about f inch 

 wide and into lengths of 2f inches for the bottom, and IJ inches 

 for the sides. These are cemented into position on one glass, 

 and when hard set the other glass is fixed on. These measure- 

 ments leave a small margin of glass at sides and bottom, and 

 the glass should be so afl&xed that the trough will stand upright. 

 For cementing I use ordinary gold size, sometimes mixing with 

 it some powdered colour to harden it. 



My ordinary "cells" (fig. 1, d) have the cell- wall made from thin 

 lead-foil such as is used for capsules ; for very shallow cells I 

 use tin-foil. I cut this material into 1-inch squares and cut out 

 the inner square of J inch, leaving a square frame J inch 

 wide, which is cemented to the centre of a thin glass slip (3x1). 

 Care must be taken to press out superfluous cement so that only 

 the smallest effective modicum is left, and the cell-wall must 

 be perfectly smooth and not thicker at one side than the other. 

 Otherwise, when in use, capillary attraction will draw the cell 

 contents to the thinner side. The same result follows if the 

 lead-foil itself is too thick, but that can be remedied by plan- 

 ing the surface carefully with the edge of another glass slip. 



The fine pipettes (fig. 1, e) are made from glass tubing of small 



