abstracts: geology 681 



being greatest at the bottom of furrows and depressions and least, 

 almost zero indeed, at the tops of the ridges. The e.m.f. will there- 

 fore, other things being equal, be greater (i.e., more electropositive) 

 at the bottoms of the furrows than elsewhere; corrosion will set in 

 here most rapidly, forming a crack which will grow narrower and 

 sharper, its rate of growth being greater the sharper it is. In time the 

 cross section of such a bar is so reduced by these cracks that fracture 

 occurs, the brass exhibiting only slight elongation (ductility) and fail- 

 ing at a stress value apparently less than the ultimate strength. This 

 explanation is borne out by the examination of a number of brass 

 failures which have occurred under such conditions. P. D. M. 



METALLURGY.— T/;e failure of brass. — 3. Initial stress produced by 

 the "burning-in" of manganese bronze. Paul D. Merica and C. 

 P. Karr Bureau of Standards Technologic Paper No. 84. Pp. 

 7. 1916. 

 In connection with the failure, by cracking, of a number of man- 

 ganese bronze valve castings in the Catskill Aqueduct at or near areas 

 repaired by "burning-in," an investigation has been made of the initial 

 stress produced in a manganese bronze double bar casting by the burn- 

 ing-in of a constrained portion. The stresses measured were in each 

 case about 8000 to 10,000 pounds per square inch (i.e., the true elastic 

 limit of the material) and the material within the burned-in area was 

 of course in tension. The microstructure of the portion adjacent to 

 the burned-in metal was not altered; the burned-in metal was in all 

 cases of finer grain than that of the casting. 



The conclusion is reached that, although distortion of a burned-in 

 casting may partially relieve the initial stresses set up by this opera- 

 tion, such castings will, in all probability, generally contain local stresses 

 of dangerous magnitude, i.e., near the elastic limit of the material. 

 Castings repaired in this manner should either be thoroughly preheated 

 or subsequently annealed in order to eliminate these stresses. 



P. D. M. 



GEOLOGY. — Some Paleozoic sections in Arizona, and their correlation. 



F. L. Ransome. U. S. Geological Survey Professional Paper No. 



98-K. Pp. 133-166, with 8 plates and 4 figures. 1916. 

 A comparison is made of ten stratigraphic sections from Bisbee, 

 near the Mexican border, to the Grand Canyon. Attention is called 

 to the thickness of the Cambrian beds in the Globe-Ray region in 



