APPENDIX A 



549 



being supported by the third and fourth fingers of the right The tube should 

 be placed at right angles upon the cutting edge, and pressed upon it with the 

 right thumb. It is then turned with the left hand in such a manner that about 

 one-sixth of its circumference comes in contact with the cutting edge. If the 

 tube is now grasp>ed in both hands with the thimib placed at the opposite side 

 of the notch (which should be outwards) and a gentle pressure be applied as 

 though it were desired to bend the glass at the point of the notch, a clean and 

 neat fracture will be the result. The sharp edges however should in every case 

 be rounded oflf by turning the extreme ends in the edge of the flame. 



If the tube is of larger dimensions a different procedure must be adopted. 

 The simplest method is to bend a length of iron wire in the form of a semi- 

 circular hook of the same diameter as the tube it is desired to cut. The wire 

 is heated to redness, and held firmly with the opening of the hook upwards. 

 The tube is then placed in the hook and turned gently against the heated wire. 

 If simple contact with the hot iron is insuflScient, the tube should be removed 

 after ha\-ing been made to turn several times against it, and the heated portion 

 of the tube touched with a cold iron. A clean circular fracture should result if 

 the operations have been carefully performed. 



The above manipulations are such as can be carried out with the aid of the 

 Bunsen flame alone. For the welding of tubes and other more advanced work 

 some form of blow pipe is essential, and a good text-book on the subject should 

 be consulted. 



THERMOMETER 

 Comparison of degrees Centigrade and degrees Fahrenheit. 



To convert degrees Centigrade to Fahrenheit — multiply by 9, divide by 5, 



and add 32. 



To convert degrees Fahrenheit to Centigrade — deduct 32, multiply by 5, 

 and divide by 9. 



