This book is being published by permission of the Chief of Ordnance, United States Army.<br><br>The material contained in this small volume was originally issued by the Ordnance Department U. S. A. and represented the results of investigative work carried on at the Watertown Arsenal. It was intended for the exclusive use of inspectors of ordnance material. The demand for the pamphlet however was considerable, and it was thought that it might serve a wider field of usefulness by being offered to others interested in the inspection of steel. It is in no sense to be considered a text book, and it is meant to present a mere outline of metallographic methods illustrating typical examples, and should be used only in conjunction with a study of text books on the metallography of iron and steel and with reference to original papers appearing in the journals bearing on this subject. It should, furthermore, be used with caution, as it is believed that metallographic diagnosis can be made only after much experience in the handling of a variety of material. This volume is intended particularly for those who are in need of some help in the interpretation of results.<br><br>The author wishes to express his appreciation of the kindly interest which Colonel Wheeler, the Commandant of the Watertown Arsenal, has shown in this as well as in other work of similar nature.