The interference method of measuring thermal expansion

This paper is in response to numerous inquiries for details of the method de- veloped at this bureau and described in Scientific Papers Nos.393 and 485, and several articles in outside publications.It is intended as a manual for the use of those who wish to measure thermal expansions by the interferometric method.As such, a more complete description of the apparatus and methods developed can be included than would be in order in a paper dealing primarily with the results of a particular set of measurements.The apparatus, method of making specimens, forms for taking data, and computation of data, each is the subject of a careful exposition.An appendix contains tables and special calculations.CONTENTS Page I. Introduction 59 II.Construction and adjustment of apparatus 61 1.The furnace 61 2. Temperature measuring apparatus 61 3. The illuminating viewing apparatus 64 III.Preparation and adjustment of the specimen 66 1. Types of sample 66 2. Methods of preparation 66 3. Adjustment 67 4. Introducing the specimen into the furnace 68 IV.Observations to be made before starting the run 68 1 .Recording thick edge of interferometer 68 2. Aperture of iris diaphragm 69 3. Initial position of fringes 69 4. Balance of storage cell against standard cell 69 5. Zero setting of galvanometer.69 6. Sensitivity of galvanometer 69 7. Initial temperature of cold junction and furnace 69 V.The run 69 1. Adjustment of the heating current 70 2. Watching the fringes 70 3.Preparing to read the temperature 70 VI.Records 70 VII.Computing and plotting 71 VIII.Appendix 73 1. Computations relating to oxidizable specimens 76