Following the ingredients of and materials used in steel, comes the heat-treatment, as the two have moved along parallel lines, in the many investigations, experiments, and improvements that have been made, and seem to be inseparable. Each change in composition seemsto have altered the heat-treatment, and each improvement in heat-treatment seem to have altered the percentage, that is best to use, of some one or more element. Many different methods and various kinds of materials have been experimented with and consequently a great deal of useful informa tion has been obtained and many improvements of a radical nature made. New methods, new materials, and new apparatus have thus been brought into use for the heat-treatment of steel. These have enabled the hardener to get more definite, positive, and uniform results, and in this way the metal has been improved to a great extent. All of the information that could be obtained on this phase of steel making and working has therefore been recorded as carefully as possible. This also suggests ideas that would indicate that there is still room for important improvements or discoveries. One of these is the attaching of a positive and negative wire of an electrical circuit to the piece of steel to be hardened and place' it in a quenching bath. The current can then be turned on, the piece heated, the current turned off, and the piece quenched without moving it or allowing the air to strike the metal and oxi dize it. Another instance is the possibilities suggested by carbonizing steel with gases or chemicals and thus doing away with the old laborious method of packing the steel pieces in bone and charcoal. Still another is the iso-minute annealing of high speed steel and the possibility of a similar method being applied to carbon steel. In gathering together the data necessary to add to my own, very little credit has been given to individuals, as to make this correct is not only a laborious but a hopelessly impossible task. To illustrate this I have seen professors claim as their own discoveries, new principles, new methods, etc., that were developed and perfected by students in their classes, and shop foremen and superintendents claim as theirs, inventions made by men in the shop. Two important discoveries that developed into new kinds of steel were made through the mistakes of workmen in steel mills. Two men on the same job added the correct percentage of a material and thus this element was twice as large as it was thought would give good results. In fact, it was believed that it would injure the metal to add more than a certain percentage, but when this maxi mum percentage was doubled the metal was given properties that were very beneficial for certain purposes. None of us can add but a mite to the knowledge that we have obtained from others and because we are enabled to write it so it will be recorded in books and papers does not give us the privilege of claiming to be the originators of certain ideas.