l886.] NEW-VORK MICROSCOPICAL SOCIETY. 59 



about five per cent, of carbon, of which more than one-half is 

 graphitic carbon. Before the metal congeals, this seems to partly 

 crystallize, forming minute laminae, which become the weak 

 places in the larger pieces of cast iron. 



" I have scales from railroad iron which are nearly one-eighth 

 of an inch in thickness. When this iron breaks, the fracture 

 does not pass through the solid portions, but follows the planes 

 of these scales. A piece of No. i cast iron, three feet long and 

 three inches by four inches thick, will break if these scales are 

 in the metal. In No. 2 cast iron these scales are smaller. I 

 have found in it one small fragment only, which perhaps con- 

 sists of a single minute lamina, and was discovered lying be- 

 tween what appeared to be crystals. 



" The scale under the first microscope is from No. i iron, and 

 consists probably of four or five layers, although it is not more 

 than ai/outh of an inch thick. Under the second microscope is 

 a specimen of No. 2 iron, and under the third microscope is a 

 specimen of No. 3 iron. In the No. 2 and No. 3 the outer por- 

 tions of the specimens are of fine texture, but the central parts 

 are almost as coarse as in No. i, which is evidence of weakness 

 of structure. 



" These laminae limit the size of castings. In the manufacture 

 of ordnance the limit where size precludes strength is soon 

 reached. Very large guns are in fact sometimes weaker than 

 small ones. 



"The graphite scale (under the first microscope) resembles 

 very closely the graphite which comes from Ticonderoga. The 

 piece of cast iron No. 2 (under the second microscope), although 

 apparently finer than specimen No. 3 (under the third micro- 

 scope), displays what appear to be crystals, also a layer-like 

 structure, the plates of which extend in various directions. 

 Between these plates cavities exist which make the iron com- 

 paratively porous." 



CONCERNING STEEL RAILS, 



Mr. Dudley, in answer to a question, remarked : " In steel the 

 percentage of graphite is very small. Bessemer steel contains 

 about Aths of one per cent, of carbon, of which a small propor- 

 tion is sometimes graphitic carbon. Steel is not absolutely 

 amorphous. Its crystals are, at present, supposed to be sur- 

 rounded by carbide of iron, it is considered that, the softer 



