164 



Lead Pencils. 



This lesson will make plain the structure and materials of 

 the most common instrument of the schoolroom, the lead pencil. 



If possible, obtain some pieces of graphite, also a cake of 

 Btove polish, and a tube of bicycle-chain lubricant. For com- 

 parison, have a bar of lead. Soak some lead pencils in water until 

 the two parts of wood will separate. Have at hand a series of 

 pencils ranging from very soft to very hard. 



Begin the lesson with an examination of the pieces of 

 graphite. The children will note the properties; heavy, black, 

 will rub off easily, and consequently will mark a paper, will soil 

 the hands, etc., (marking by a substance will be seen to be a rubbing 

 off of a part of that substance). It is also very smooth, being soapy 

 to the feel of the fingers. This is graphite, the substance which 

 forms the center part of our lead pencils. It is not lead at all. 

 Now compare with real lead. It is soft, will mark a paper also, 

 but is quite different from graphite. Graphite used to be called 

 black lead, and this gave the name to the pencils. 



The children may now listen with interest to an account of 

 how lead pencils are made. The graphite is reduced to a very 

 fine powder and mixed with water into a sort of black mud. A 

 similar mixture of fine clay and water is made. Then a mixture 

 of these two is placed in a press, which has for a bottom a sieve- 

 like plate, the holes being the size of the leads for the pencils. 

 Great power is brought upon the press, forcing the thick paste 

 thru the holes. This makes long, slender "leads." These are 

 placed on boards, dried, and then baked in a hot oven. 



Two pieces of wood are prepared, as the soaked pencil will 

 show, which are to be glued together. In one is sawed a groove 

 into which the lead fits exactly. After the two pieces are glued 

 together, the whole is turned round or cut into octagonal or other 

 shapes, polished, varnished, and the name pressed on. 



