170 CONSTRUCTION OF APPARATUS. 



chest, but of the mouth, which should be blown out like a 

 trumpeter's, while the breathing has to be carried on through the 

 nose only. First practise without the blowpipe in the mouth, 

 inflating the cheeks, and while inflated breathe through the nose ; 

 then, without opening the mouth, force the blowpipe between the 

 lips, and.it will be found that the escape of air from the blowpipe is 

 so little that the process of breathing with inflated cheeks can be 

 continued, and thus a steady flame procured. If the pointed end 

 be held inside the flame, and a current of air be directed across it a 

 little above the wick, the flame is thrown to one side in the form of 

 a pointed cone. In the present case the only reason for using the 

 blowpipe is to obtain a flame which is directed downwards ; it is not 

 necessary that the fla,me should be steady., but care must be taken 

 not to crack the glass or char the sealing-wax by the excessive heat. 

 Since the plate which forms the bottom of the vessels will have 

 to be suspended from the balance, a hole must be drilled through 

 its centre, and widened to about 4 mm . Further, a screw is to be cut 

 from end to end of a piece of brass wire, 7 cm long and from 3 to 4 mm 

 thick, care being lakeii in cutting it to hold the die-stock perpen- 

 dicular to the wire, or the nut which is to be used with the screw 

 will not be horizontal. The wire must be straightened previously, 

 and to avoid flattening it, this must be done with a wooden hammer 

 upon a wooden support, after the wire has been made red-hot and 

 allowed to cool. One extremity of the wire is filed flat on both 

 sides, for a short distance, and a hole is drilled through the flattened 

 end, through which a thread may be passed afterwards. Round the 

 other end a small leaden weight is fixed, about 15 mm thick and r2 mm 

 high, by inserting the end into the mould already described. While 

 the lead is poured into the mould, the wire is kept in the proper 

 position by fixing it in the fork of the retort-stand. 



The nuts are made of brass, about 2 mm *5 thick. Two pieces, 

 each about 10 mm square, are cut out of a sheet of brass with the help 

 of a saw or a chisel. Fig. 122 shows a * frame-saw,' which is usually 



FIG. 122 (| real size). 



employed for cutting metal. The frame is made of iron, and forms 

 three sides of a rectangle, of which the blade forms the fourth side. 

 Two square pieces of iron, one at each end of the frame, are provided 



