Mauch 2. 1883.] 



SCIENCE. 



101 



Microscopic analysis of the structure of iron 

 and steel. 



BY J. C. BAYLBS OF NEW YOEK. 



After briefly reviewing the worlc of A. Martens of 

 Berlin and Di\ H. C. Sorby of Slieffield in this field 

 of research, Mr. Bayles considered the methods of 

 preparing specimens for microscopic study whicli in 

 practice lie had found to give the best results, and 

 continued: The first step to be taken in practical 

 microscopy is tlie training of the eye to observe what 

 may be seen without tlie aid of a lens. This is ac- 

 complished by tlie patient examination of character- 

 istic fractures, and noting similarities and diiferences. 

 After the nalced eye has become familiarized with all 

 it can see, the student should continue his investiga- 

 tions assisted by a hand-lens with a power of from 

 two to tln-ee diameters, and absolutely achromatic. 

 Specimens to be studied with a view to determining 

 their internal structures should be surfaced in a 

 planer, and smoothed by draw-filing in the direction 

 of the fibre. The surface thus obtained is treated 

 with slightly diluted nitric acid, which gives a rapid 

 and wide development of tlie structure, wliich may be 

 studied with advantage while it lasts, and will prepare 

 the student for finer work. For fine development more 

 care and time are needed. After planing, the surface 

 of the metal is ground with fine emery, or under a 

 metallic mirror-grinder. It is then treated with acid, 

 Mr. Bayles describing the manner in great detail. A 

 thoroiigh development with weak acid requires from 

 twenty-four hours to six days, according to the com- 

 position of the metal. Small specimens are iirepared 

 by iilaning down from the back to a thickness of ;ni 

 to n; of an inch. The planed face is then d!round 

 and surfaced on a fine whetstone, developed with 

 weak acid, and moimted between glasses with Canada 

 balsam. In selecting a microscope, care should be 

 taken that the lenses give a good definition, that there 

 is no 'shake' or lateral motion in the adjustments 

 for focus, and then the table should admit of inclina- 

 tion at any angle found most convenient for observa- 

 tion. Concerning the results to be expected from the 

 mici'oscopic analysis of metals, Mr. Bayles expressed 

 the belief that it opens a vast field of knowledge not 

 yet reached by either chemical analysis or physical 

 test. There are many conditions, the result of changes 

 produced by meclianical treatment, to which chemi- 

 cal analysis gives no clew, and which are detected, 

 but not explained, by the tests of the physical labora- 

 tory. The microscope will, no doubt, explain many 

 of the mysterious changes which occur in metals of 

 given chemical composition under different condi- 

 tions, and will give the metallurgist an opportunity 

 of studying the anatomy and physiology of iron and 

 steel, which, in a most important sense, will supple- 

 ment analysis and mechanical test, which have thus 

 far, to some extent, rim in parallel lines. When, be- 

 tween the report of analysis and the fracture of the 

 broken test-piece, we can place a polished longitudinal 

 or cross-section of the material, its internal structure 

 developed by acid, and admitting of careful micro- 

 scopic study, we are furnished with the missing link 

 in the chain of evidence required for a correct con- 

 clusion as to the nature of the material under inves- 

 tigation. 



Coal and iron of Alabama. 



BY DU. T. STEHRY HUNT OP MONTREAL. 



After referring to the researches of Profs. R. P. Roth- 

 well and Eugene Smith, and complimenting them in 

 higli terms on the results of their labors in that sec- 

 tion. Dr. Hunt said that the existence of coal in Ala- 



bama had been known for half a century: it forma 

 a part of the great Appalachian coal-basins, which 

 lie principally upon the waters of the Ohio, and has 

 an extent of 58,000 n miles, including eastern Ten- 

 nessee, the north-western corner of Georgia, and a 

 large part of the state of Alabama. The principal 

 part of these measures has an area of 5,000 D miles; 

 but on the east side are two small detached basins, — 

 the Cahawba, 2-30 D miles in extent, and the Coosa, 

 100 D miles. They are separated from the main basin 

 by narrow belts of older rocks a few miles in width; 

 and there is no doubt that they arc detached portions 

 separated, —the one by a fault pure and simple, the 

 other by an undulation which has overturned the 

 folds, and has faulted them in some places. To 

 the east of these, stretches the Coosa valley, a geo- 

 graphical feature of the greatest importance, being a 

 continuation of the great limestone valley which 

 runs up to Lake Champlain. On the eastern border 

 of the valley is a great belt of crystalline rocks, of 

 which the Blue Ridge, Hoosac Mountain, etc., are a 

 part, and forming the great Atlantic belt from the 

 hills of New England to Alabama. Next is a lime- 

 stone valley forty or fifty miles in width. Then we 

 have the North Mountain, which is the beginning of 

 the great series of folds which make up the Alle- 

 ghany Ridge, and formed of paleozoic rock which 

 underlies the coal. To the west are the great coal- 

 measures, essentially the same in character as those 

 of Pennsylvania and Virginia. A peculiarity of the 

 underlying bed of sedimental rock is its varying 

 thickness, from 18,000 feet in Huntington Coiinty, 

 Penn., and diminishing toward the south, until .in 

 some" places in Alabama it has thinned down to 

 1,800 or even 1,000 feet of soft rock, sandstone, and 



Tlie ores in the limestone valley are limonite, and 

 the brown hematites found in Berkshire County, 

 Mass., enormously developed ; furnishing a large part 

 of all the ore which is smelted, and practically inex- 

 haustible for generations to come. In the mountain 

 belt is another set of iron-ores, also important, — the 

 red hematites of the Clinton group. Beyond that 

 are coal and occasional clay ironstones, of secondary 

 importance as regards amount. In the northern por- 

 tion of these beds, especially in Pennsylvania, the 

 North Mountains separate the coal and iron by dis- 

 tances of 100 miles or more, offering serious draw- 

 backs, and increasing the cost of production; at the 

 same time the Atlantic belt renders it impossible to 

 reach the region by navigation. But a remarkable 

 fact is the almost complete disappearance in Alabama 

 of the two great mountain barriers before reaching 

 the sea, being thinned out and worn and ground 

 away. The soutliern rim of the basin is bi-oken 

 down, and the coal and iron are on a level with the 

 navigable waters of the gulf at Mobile; bringing up 

 the question of the importance of rendering the rivers 

 navigable so as to reach the heart of the coal-region. 

 The coal-measures to the south suffer no diminution 

 in quantity or quality; but the bed-rocks are so up- 

 turned and folded and faulted, that within three or 

 four miles the coal and iron are found together. A 

 curious fact of the enormous fault — this great break 

 in the strati tication of nearly 10,000 feet — is, that it 

 has brought up the hematite ores directly beside the 

 coal in the Cahawba valley, so near that by the sim- 

 ple means of gravity they may be brought to a com- 

 mon point, reducing the cost of production to the 

 lowest. To these geographical and geological con- 

 ditions the region owes its future importance. It 

 is the part of the country which is growing most 

 rapidly in population, showing an Increase in ten 



