ZAY JEFFRIES 201 



witliin the proper limits of grain size are not subjected to the working 

 process, which costs on the order of twenty times as much as the 

 preparation of the ingot. 



The method of quantitatively determining the grain size has been 

 described by the author in the Transactions, of tJie Faraday Society.^ 

 A circle 79.8 millimetres diameter is drawn on a ground glass, and the 

 image of the properly etched sample is brought into good focus. The 

 grains intersected by the circumference of the circle are counted and 

 multiplied by .5 (in the paper above mentioned this factor was given as 

 .6, but later results show that .5 is both more accurate and simpler to 

 use),f and this product is added to the number of grains completely 

 included. The sum is the number of whole grains within the area 

 represented by the circle. 



It is true that the determination of grain size in other metals, such 

 as alpha brass, has been used as a help to works control, but the 

 application of this is not very extensive and not as necessary as with 

 tungsten. Other differences are manifest which may be easier to deter- 

 mine than the grain size. Several metallographists have told the 

 writer that they had investigated the variations in grain size and found 

 that the physical properties did not vary greatly with considerable 

 variations in grain size, and hence they had concluded that the test was 

 not suitable for their purposes. It is for this very reason that the 

 writer believes that many other special cases will arise in which a 

 considerable change in grain size will correspond to but slight differ- 

 ences in certain other properties (like the working properties in tung- 

 sten), and these properties may be controlled within narrow limits by 

 controlling grain size. In fact, metals or alloys other than tungsten 

 have certain properties which can be controlled only by controlling 

 grain size or other structural features, but these structures are pro- 

 duced by uniform processing determined by experience, and the actual 

 quantitative determination of grain size is not necessary. With the 

 modern demand for uniformity of product and high standards, the 

 manufacturing tolerances will be reduced, and extended use of grain 

 size control may be expected. Even now the defective loss in the 

 mechanical working of metal could be reduced in many instances by 

 properly controlling the grain size in the various stages of processing. 

 In large plants the lessening of the defective loss a fraction of one per 

 cent, would more than pay the cost of investigation and upkeep of 

 these control methods. 



* Vol. XII, Part I, iQi/, p. 40. 



t Metallurgical & Chemical Engineering, p. 185, Feb. 15, 1918. 

 Also Sano and Ohashi, Proc. of the Physico-Mathematical Society of 

 Japan, 3rd Series, Vol. I, No. 7, p. 216, treat this method of grain size 

 determination mathpmatically, and conclude that "Jeflfiries' formula . . . 

 is quite sufficient for practical purposes." 



