372 THE YOUNG FAKMER'S MANUAL. 



may be able to forge and finish up edge tools in the neatest man 

 ner, and be incompetent to temper them well. This is an art 

 which is acquired by the exercise of mechanical skill, and long 

 experience. A workman may " hit " upon the right temper in 

 one tool, and then, if he is not a natural mechanic, and if his ob 

 servation be not very close, and perception very quick and keen, 

 he may fail to get the correct temper in tempering a score of tools 

 exactly like the one he had tempered so well. The idea to 

 be kept in mind in tempering edge tools is, to have the whole steel 

 tempered so as to make a good cutting edge as the edge wears 

 away. Tools are tempered many times so that the cutting edge 

 is first-rate until one-fourth of an inch or so is worn off, and 

 then they become poorer and poorer as the edge is worn away, 

 when they are worthless until they are re-tempered. And many 

 times the first edge of a tool is very poor ; but after it has been 

 ground two or three times the edge will continue to grow better 

 until it is worn out. But if a tool is tempered as it should be,*lt 

 will hold as good an edge when it is half worn out as it did when 

 it was new. 



533. When a piece of steel is heated to redness, and immedi 

 ately plunged into cold water, it is rendered as hard as it can be 

 made, and as brittle as a file, which possesses no tenacity. 

 When steel is heated to certain different degrees it emits differ 

 ent colors, each color corresponding to the different degrees of 

 heat. For example : if we heat the end of a steel bar, or chisel 

 which has good steel on the end, to redness, and thrust the end 

 into cold water and cool it for an inch or two from the end, if the 

 steel is not rusty, by looking attentively at the steel between the 

 hot and the cold steel we shall discover several colors. As the 

 cold steel is being heated up, a kind of greyish color will be per 

 ceived, and a little farther towards the hot part of the tool the 

 steel will assume a kind of straw color ; and between this color 

 and the hot portion the steel will assume a sky-blue color. Now 

 when all these colors are discovered in ordinary steel, if the whole 

 were plunged into cold water and cooled, those parts of the tool 

 which presented different colors would possess different degrees 



