CONSTRUCTION OF PUMP 299 



The barrel and the suction-tube are fixed into these pieces ; the 

 suction-valve is made of oiled silk. 



Cut a circular plate of zinc, 5 cm in diameter, and about 0*5 or 

 Qmm-75 thick. Punch a hole in the middle, 3 mm wide, and also a few 

 holes near the edge, for screwing the plate to a board; the raised edges 

 of the punched poles are hammered flat with the mallet, the middle 

 hole especially being made smooth all round with file and rimer. 

 Take a strip of sheet zinc, 5 cm long and 25 mm wide, hammer it over 

 a round piece of wood or iron rod into a small tube, and solder one 

 edge upon the other by holding the tube horizontally over the spirit- 

 lamp. File it smooth at both ends, hold the plate horizontally over 

 the spirit-lamp, place the tube with one end upon the middle of the 

 plate, and solder the tube to it. Another strip of zinc, 2 cm wide, and 

 three and a half times as long as the external width of the glass- 

 tube, is similarly bent into a tube, soldered along the edges, and by one 

 of its ends to the plate. The narrower tube is for this purpose held 

 by the pincers, the plate uppermost and the wider tube placed upon 

 the upper side of it; to prevent the parts from being displaced 

 while being soldered together, a thin iron wire may be laid across 

 the top of the wider tube, bent down on both sides, and twisted 

 firmly across the lower end of the narrow tube. The small strip of 

 metal by means of which the valve is secured, Bin fig. 168 (7, should 

 be soldered to the plate at the same time ; it is about 6 mm wide, and 

 its form and other dimensions are seen from the figure. The solder 

 should be used sparingly, all joints should be just filled with it, but 

 none must be allowed to run about, or otherwise the interior of the 

 little strip B may possibly be filled with it, or drops may spread over 

 the plate, render its surface uneven, and prevent the valve from pro- 

 perly closing. Every trace of soldering fluid should be removed 

 afterwards with water, the water then dried up, and both tubes 

 heated until a bit of sealing-wax melts upon their inner surface. 

 Upon the inner edge of each tube a layer of sealing-wax is spread, 

 ibout 6 or 8 mm wide and l mm thick, and then allowed to cool. Next 

 ix a piece of yellow transparent oiled silk, v, 8 mm wide, and 10 'or 

 I2 mm long, in the manner shown at C of fig. 198, by placing one 

 nd underneath the bent strip J5, and then pressing down the strip 

 : 9 with some blunt tool until the piece of oiled silk is firmly 

 ;lamped. The two glass tubes which are to represent the barrel 

 i-nd the suction- tube (the latter of which may be of any length), are 

 hen heated and pushed into the metal collars. The latter should 

 lot be heated, or the piece of oiled silk would be spoiled ; instead 

 >f the oiled silk a thin flat piece of india-rubber may be used, such 

 s may be cut out of a broken india-rubber band. 



