94 Laboratory Arts 



a teacher preparing or delivering a lecture. In addition it 

 should be remembered that soda-glass of good quality needs 

 little annealing ; that is, indeed, one of its essential properties ; 

 consequently there is much to be said in favour of the view 

 that one should subject a piece of glass work to heavy strains 

 immediately after making it, as it is better that it should 

 crack then, than during a demonstration. Once a piece of 

 work is completed, treat it carelessly do not anneal ; put it 

 down and let it cool as it may : pull it in various directions, 

 etc. ; so that if it survive, its reliability is assured. A beginner 

 will have considerable objections to such a procedure ; it is not 

 an uncommon thing to see a beginner surround himself with 

 examples of glass working upon which he dare hardly breathe, 

 and his distress is very marked when a friend destroys one 

 piece after another in merely handling while examining it. 

 Work such as this is fit only to be destroyed ; it certainly is of 

 no use in apparatus fitting, and would be a source of endless 

 trouble and annoyance to any lecturer into whose hands it 

 might pass. In addition, the maker has evidently not mas- 

 tered the correct methods of work. It is painful to watch the 

 intensity of expression on the face of a beginner when a 

 " clumsy " teacher in handling breaks a piece of glass work at 

 which the student has hardly dared to look since it was made, but 

 the best test of the efficiency and correctness of the work is to 

 subject it to a greater strain than it will ever have to bear in 

 actual work. Glass work is not made simply for exhibition 

 purposes. 



This applies in the main to the smaller pieces of apparatus, 

 such as T, Y, U-tubes, Wiirtz-flasks, etc. there is, of course, a 

 reasonable limit in all things, and one is justified in taking even 

 special care of a Hoffmann's Voltameter or similar apparatus, 

 which it would be folly not to anneal. 



In the following exercises, students are recommended to 

 commence work with 2o-cm. lengths of 4-mm. bore tubing, and 

 to increase the diameter of the tubing and the thinness of the 

 walls as success rewards their efforts. 



Tubing need not always be cut, it should usually be drawn 

 out before the blowpipe, as this produces a closed end on each 



