72 Laboratory Arts 



should then be ground on emery-paper, moistened with 

 camphorated turpentine. 



Broken reagent bottles, stock bottles, measuring cylinders, 

 gas jars and many other articles may have their usefulness 

 renewed by treatment such as this. Measuring cylinders, 

 so cut down, should have the tops bordered, not ground, by 

 holding in a large blowpipe flame, and rotating carefully until 

 the edges soften. A piece of conical carbon is then used 

 to widen out the opening, and, while still hot, one portion 

 about |" wide is more strongly heated and a lip is bent out- 

 wards by means of one edge of the carbon, or the triangular 

 copper piece shown on p. 84. 



Cutting Glass Tubes. A second method for the cutting of 

 measuring and similar jars, but which answers best with thinner 

 glass vessels, such as beakers, test tubes, and ordinary glass 

 tubing of all diameters, consists in leading a crack round the 

 glass. The difficulty is in starting a crack successfully. A 

 file cut is made at the desired place, and extended to 

 a length of about f". The middle of this is then touched with 

 the red-hot point of a glass rod, not more than " in diameter. 

 The hot glass should not be in contact more than one second, 

 and a crack will usually start from that point along the file 

 mark in both directions. This crack may now be led in any 

 direction, indeed specially shaped vessels may be cut out fairly 

 easily. For instance, a model bucket or tub, Fig. 61, has more 

 than once been cut from a beaker in this way, no 

 difficulty being experienced in leading the crack 

 round the lugs, provided too great a distance was 

 not attempted each time. To lead the crack 

 along, the same hot glass rod is used as before, 

 but it should not touch the glass, though ap- 

 proaching as nearly as possible to it immediately in front of 

 the crack. The crack will then continue as far as the hot 

 rod, where it will again stop. In this way the crack may 

 be led completely round the cylinder, or in whatever direction 

 it may be desired. 



In cutting glass tubing of diameter larger than f", this 

 method of touching a file cut with the point of a hot glass 



