8 4 



Laboratory Arts 



pumps have all been tried, but there is no satisfaction in any 

 device that gives a continuous stream of air at constant pressure. 

 The use of an indiarubber chamber stored with air at a foot- 

 controlled pressure really adds a third hand to the glass blower, 

 who controls his flame through the air pressure, and this with 

 the foot. With any continuous supply a tap is necessary in 

 order to alter the pressure, and unless this is worked with the 

 knee, or some similar contrivance arranged, the operator must 

 release one hand from his work. In our work, where the 



(a) 



2HE 



(d) 



FIG. 73. Glass-working tools. 



maximum amount of variation is required, and no two "jobs" 

 are alike, control and variation is of the utmost importance, 

 and experience shows that two blowpipes cannot be driven 

 satisfactorily from the same bellows, nor from a continuous 

 supply of air, unless the work to be done is continuously alike. 

 Tongs, etc. A pair of flat tongs such as shown in the 

 sketch should be available ; a triangular piece of copper ~Q" 

 thick in a handle, for opening tubes, etc., or a block of com- 

 pressed charcoal shaped to a conical point, and a pair of fine- 

 pointed forceps will be found useful. See Fig. 73. 



