ABSTRACTS: CERAMICS 329 



TECHNOLOGY. — Location of flaws in rifle-barrel steel by magnetic 

 analysis. R. L. Sanford and Wm. B. KouwEnhoven. Bur. 

 Standards Sci. Paper 343. Pp. 21, pis. 3, figs. 13. 1919. 

 This paper describes an investigation which was undertaken for the 

 purpose of determining whether an appHcation of magnetic analysis 

 was practicable for the detection of flaws in rifle-barrel steel. By means 

 of apparatus especially constructed for the purpose a large number of 

 bars were explored for magnetic uniformity along their length. In 

 spite of the fact that these bars were taken from material which had 

 previously been rejected as the result of drilling tests, not one was 

 found which contained a pipe. The results obtained, however, demon- 

 strated that the method is amply sensitive to detect and locate flaws. 

 Further study is necessary to determine to what degree the sensitivity 

 of the apparatus should be reduced in order not to cause the rejection 

 of material which is satisfactory for all practical purposes and also to 

 determine the type and magnitude of the effect which will be produced 

 by a pipe. For this reason the work is being continued by the Win- 

 chester Repeating Arms Company who cooperated in the investigation 

 and at whose plant the apparatus has been installed. R. L. S. 



CERAMICS. — The cooling of optical glass melts. Howard S. Rob- 

 erts. Joum. Amer. Ceram. Soc. 2:543-563. July, 1919. (Geo- 

 physical Lab. Papers on Optical Glass, No. 14.) 



The conditions to be attained when a melt of optical glass is cooled 

 in the pot are: (i) that neither ream nor bubbles shall be introduced 

 during the cooling, nor carried into the middle of the melt; (2) that 

 the glass shall not become inhomogeneous through the precipitation of 

 a crystalline phase; (3) that the bulk of the cooled melt shall be found 

 cracked into large, reasonably rectangular blocks, having smooth, flat 

 surfaces; and (4) that these blocks shall be sufficiently free from strain 

 to cleave readily with a smooth fracture. 



The appearance of ream in the middle of the melt, vacuum bubbles, 

 or a crystalline phase, can be discouraged by rapid cooling, preferably 

 from the bottom of the pot, while the glass is still soft; and by insulating 

 its top surface as soon as the melt is set out of the melting-furnace. 



The cold melt shows cracks of two types: "spherical cracks" and 

 "plane cracks." The presence of either type of crack in the melt 

 reduces the tendency for the other type of crack to form. As the frac- 

 ture due to spherical cracks is rough and the pieces formed are irregular, 

 while that due to plane cracks is entirely satisfactory, it is desirable to 

 maintain the temperature gradient at a low value by slow cooling, and to 



