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when necessary, be erased is a great further convenience. An- 

 other very important use depends on the infusibiiity of graphite. 

 Although it can be burnt to carbon dioxide it is ignited with great 

 difficulty. This property, together with the infusibiiity just men- 

 tioned, fits it for making crucibles, retorts, twyer pipes and similar 

 purposes. (Twyer pipes are the pipes through which air is blown 

 into furnaces, e.g., into the blast furnaces used in smelting iron). 

 For crucibles it is freed from grit, mixed with Stourbridge clay, 

 and made into a paste with water. The kneaded mass is left to 

 itself for a long time, several weeks as a rule, then moulded, very 

 slowly dried and very carefully fired. Crucibles made in this way 

 are very largely used in metallurgical operations. The Morgan 

 Crucible Company, Limited, very kindly supplied me with a set of 

 lantern slides for exhibition in this lecture, illustrating the use of 

 their crucibles in a number of such operations. At the present 

 juncture in national affairs this particular class of the uses of 

 carbon is of special interest. Graphite crucibles are playing an 

 important part in that marvellous production of munitions of war 

 upon which so much depends and without which we should not be 

 here in security giving a lecture or listening to it, but should 

 either be dead or miserable captives of the modern Sennacherib. * 



The smoothness and slipperiness of graphite make it of great 

 value as a lubricant for diminishing friction. Sometimes it is used 

 dry, at other times mixed with grease or oil. It is extensively 

 employed in connection with machinery or various kinds to ensure 

 the smoth running of the moving parts. The bicycle chain is one 

 of the most familiar examples. In making boots and shoes 

 powdered graphite is often placed between layers of leather in the 

 sole and at the junction of the " waist " of the boot with the sole 

 to prevent the squeaking noise which is so objectionable. Black- 

 lead is also used in the joints of artificial limbs. A special but 

 melancholy interest attaches to this particular use at the present 

 time when so many of our gallant soldiers are obliged to resort 

 to artificial substitutes for limbs lost in the service of their 

 country. 



The unalterability of graphite in air renders it suitable for 

 protecting metallic surfaces. Sometimes it is mixed with linseed 

 oil and applied as a paint, whereas it is used dry for protecting 

 and polishing stoves. Unlike the diamond, graphite is a good con- 

 ductor of electricity and hence is used in electrotyping. Suppose 

 it is desired to copy a seal in copper. An impression is made in 

 wax or other suitable plastic substance. As wax is a non-con- 

 ductor of electricity we cannot deposit the copper upon it direct, 

 but, if coated with graphite, we can do so easily. There are other 

 electrical uses of graphite, some of which I may mention later, 

 but for the present use we will pass on to the third form of carbon, 

 the amorphous, of which charcoal is one of the most familiar 

 examples. Wood charcoal is prepared by the action of heat upon 

 wood with more or less complete exclusion of air. The old 

 method, suitable for use when wood is abundant, is to build a 



