August ii, 192 i] 



NATURE 



76. 



the use of a ball of this size is limited to specimens 

 not much less than one-tenth of an inch in thickness 

 and half an inch in width. In 1913 the necessity 

 arose for the accurate determination of the hardness 

 of the walls of small-arm cartridge-cases at different 

 positions along the length. The thickness of wall, 

 diminishing in some cases to about one-hundredth of 

 an inch near the shoulder, is quite insufficient for the 

 application of the usual Brinell test. Accordingly, 

 a machine was designed and constructed by Messrs. 

 H. Moore and R. ^Iather for the Research Depart- 

 ment, Woolwich, in which very small balls with cor- 

 respondingly small loads could be employed. A descrip- 

 tion of this machine has been given bv Mr. Moore in 



Fig. I. — A smaU Brinell hardness testing machine. 



the Proceedings of the Institution of Mechanical 

 Engineers of January, 1921 It was designed to 

 permit of great latitude in the dimensions of the test 

 specimen, of the use of various sizes of ball from 

 I mm. diameter upwards, and of loads from 5 to 

 100 kg. The first machine was in continuous use 

 during the war, and was the subject of a secret patent 

 (Craig, Moore, and Mather's patent), which, how- 

 ever, has now been published. The illustration 

 (Fig. i) shows a simplified form of the machine con- 

 structed by Messrs. Alfred Herbert, Ltd., of Coventry. 

 The machine stands upon a base-plate furnished 

 with levelling screws. This plate supports two ver- 

 tical threaded columns which carrv the table for the 



reception of the specimens to be tested. By turning 

 the hand-wheel at the side of the machine the table 

 mav be set at the required height. The load seen 

 in the lower part of the photograph is composed of a 

 set of graduated cylindrical weights totalling 50 kg» 

 It is carried by the loading stirrup, to the upper por- 

 tion of which is attached the ball-holder. The ball 

 is fastened to the ball-holder by india-rubber solution 

 so as to render the changing of balls an easy matter. 

 The most important point in the design of the ap- 

 paratus is the method by which the load is transferred 

 from the cross-head of the machine to the specimen 

 under test. By turning the hand-wheel at the top a 

 non-rotating screws of fine pitch can be raised or 

 lowered. The lower end of the screw carries a sus- 

 pension stirrup, which is prevented from rotating bv 

 arms bearing against the columns, and from this sus~ 

 pension stirrup is hung the loading stirrup by means, 

 of a ball-and-socket joint. When the stirrup is 

 lowered gently, so that the ball rests upon the speci- 

 men, the loading stirrup becomes free and discon- 

 nected from the suspension stirrup. At this stage the 

 whole of the weight is upon the specimen, there being 

 no parts in friction or rubbing contact. The upper 

 hand-wheel is then turned back to take the load off 

 the specimen, which can now be removed for the 

 purpose of measuring the diameter of the impression 

 bv means of a high-power microscope with gradua- 

 tions of 1/200 mm. on the graticule. The hardness 

 numbers are calculated as in the ordinary Brinell test, 

 the load being divided by the area of the impression, 

 and are directly comparable with the usual Brinell 

 numbers when a load proportional to the square of 

 the ball diameter is employed. 



The impressions are so small as to be scarcely 

 perceptible to the eye, and tests may be made on 

 parts of delicate mechanisms without injury to the 

 part tested. Loaded srnall-arm cartridge-cases may 

 be tested without removal of bullet or charge. The 

 hardness of wire at successive stages of draw'ing can 

 be measured. Cutlery blades, how^ever thin, may 

 be tested, and the hardness of a cutting tool may 

 be determined close to the cutting edge. Interesting- 

 applications of this microscopic Brinell test have been 

 made in the exploration of strain-hardening, for when 

 a metal object has been unequally strained the dis-. 

 tribution of strain will usually be indicated by differ- 

 ences in hardness from point to point. 



Attention may also be directed to the micro-Brinell 

 apparatus developed by the Ordnance Department of" 

 the U.S. Army (Bureau of Standards, Bulletin 16, 

 1920, p. 557). This has been used w^ith a load ot 

 15 kg. for 30 seconds upon a ball 1/16 in. in dia- 

 meter for measuring the hardness of individual' 

 crvstals or small aggregates in annealed carbon steels, 



H. S.A. 



The Coal-mining Industry. 

 Bv Prof. H. Louis. 



T^HE July issue of the Quarterly Review contains 

 -*• an article upon the recent coal dispute by Dr. 

 Arthur Shadwell, to which he has given the some- 

 what unfortunate title "The War of the Mines." Dr. 

 Shadwell points out at the beginning that this dis- 

 pute was really not a war, and that there was in 

 reality no need at all for a difference, which might 

 have been arranged by mutual concessions, to have 

 degenerated into industrial strife. He recognises that 

 this was not a case of the men striking against any 

 arbitrary action of the employers, but was rather an 

 expressfion of their irritation at the inevitable develop- 

 ment of the economic situation, and he states clearly 

 and definitely the only remedy: "There is only one 



NO. 2702, VOL. 107] 



way out — the way of work. Other nations in a 

 similar position have taken it ; they are at work, 

 and working hard. Here less work is being done 

 than ever before." 



It is pointed out quite correctly that the mining 

 industry is distinguishing itself above all others in 

 the readiness with which it resorts to industrial strife, 

 and that the real cause of many of these difficulties, 

 and the basal reason for the present grave position 

 of the coal industry, are to be sought in the Minimum 

 Wage Act of 19 11, which is accurately described as 

 "the first instance of a minimum wage established 

 by Parliament in an industry in which the workmen 

 are well organised and able to protect themselves." 



