Glass Working Cutting, Grinding, and Drilling 73 



rod should always be followed in the end it will be found 

 much more satisfactory, and a saving of energy. Should it 

 ever be necessary to cut a wide glass tube from a file mark 

 only, the tube should always be wrapped in a duster, as wide 

 tubes crack from a file cut in various directions, and severe 

 wounds are sometimes caused in consequence. Jena glass 

 tube should be cut by the paper strip and blowpipe 

 method without exception^ the glass being too strong to cut 

 from a file mark by breaking, and too refractory to crack 

 upon the touch of a hot rod. Care should be used in grind- 

 ing Jena tubing, owing to its tendency to shatter, and when- 

 ever the grinding can be replaced by rounding and bordering 

 in the flame, this method should be adopted. 



In cutting narrow glass tubing and rod, a file mark is 

 made (one cut forwards should be enough), with a file 

 moistened with camphorated turpentine. The thumbs are 

 placed opposite this mark, and the tube pulled rather than 

 bent a little of each, in reality. Usually the tube so treated 

 breaks exactly at right angles, and gives an even edge. 

 Only tubes less than f" diameter should be cut in this way. 



All glass tubes used for building up apparatus should 

 have their ends bordered or rounded by the action of a 

 blowpipe or Bunsen flame, but the tube should never be 

 allowed to collapse, or even partially collapse, as this constricts 

 the bore. Glass rods for stirring should be similarly rounded 

 at the ends, but not allowed to become so hot as to collect 

 into a piece of larger diameter than the rest of the rod. 

 Stirring rod should usually be of small diameter, a ~Q" rod 

 being none too narrow; it is better to break a rod than a 

 beaker. 



2. Grinding Glass. Glass to be used for making up into 

 cells, boxes, etc., should have its edges ground. This is done 

 by moistening a sheet of emery-paper with a ro-per-cent. 

 solution of camphor in fresh turpentine. 1 The effect of this 



1 Turpentine polymerizes somewhat easily, and the higher polymers are 

 not suitable for this purpose, being somewhat sticky and inclined to 

 solidify hence the turpentine used should be freshly distilled, and have 

 very little odour. The B.P. should not exceed 156 C. 



