400 EXPERIMENTS WITH THE FLAME-MANOMETER. 



stretched across it ; the second half of the capsule, over the rim of 

 which glue has also been spread previously, is then placed upon the 

 first. The whole is then pressed together moderately in the vice 

 and kept there until dry. The glue along the joint and the projecting 

 portions of the gold-beater's skin are afterwards removed with a sharp 

 knife. The tubes are of glass ; their shape and size appear from the 

 figure ; the aperture of c should be about O 1 * 1 '^. The vertical portions 

 of the tube 6 may be clamped in the retort- stand. It is advisable to 

 varnish the capsule outside several times with asphaltum varnish, 

 until the surface has a glossy appearance when dry ; this is done to 

 render the wood gas-tight, which unvarnished wood is not. 



For the capsule a large cork may be substituted. It is cut across 

 the middle, the necessary holes are bored in it for the tubes, and a 

 conical cavity is cut into %ch half with a sharp penknife, as shown in 

 fig. 234, B. Large corks are never quite air-tight ; the whole of the 

 outside should therefore be covered with a layer of sealing-wax 1 

 , or 2 mm thick ; this is done after the two halves have been glued to- 

 gether and the whole is perfectly dry. 



For the reflecting box four square pieces of common looking-glass 

 must be procured, each 14 cm long and 12 cm wide ; the bottom of 

 the box is made of a square of very stout pasteboard, each side being 

 14 cm long. In the middle of the square a hole is made, 5 mm wide, 

 for attaching it by means of a screw to the disc of the whirling-table. 

 The upper side of the box is left open so that the arm may con- 

 veniently reach the screw. The sides of the box are first joined 

 together by strips of paper, 1*5 or 2 cm broad, over which moderately 

 thick glue is spread in a very thin layer ; when the glue is dry, the 

 edges are fastened together by pieces of black linen tape, 2 cm- 5 wide, 

 using for the purpose rather thick glue. Four pieces of the length 

 required are first placed along the vertical edges. Two pieces are 

 then placed all round the box, one round the upper, the other round 

 the lower edge, and the length of these pieces should be such that 

 the ends may overlap one another for 2 or 3 cm . This is the 

 best way of protecting the box against the action of the centrifugal 

 force which tends to separate the sides from one another. Of these 

 two pieces of tape half of the width is glued all round, above and 

 below, to the outside of the box ; the other half is turned inside 

 at the upper edge, and folded round upon the bottom of the box at 

 the lower edge. At the four lower corners, the tape must be cut 

 half-way across, so that it can be placed flat upon the bottom with- 

 out making folds. 



The flame should be about 10 or 15 cm distant from the box. To 

 protect the flame against the current of air which arises when the 

 box is turned, a. jjlass tube is placed over it. The narrower portion 



