-202 abstracts: technoi^ogy 



PHYSICS. — Preparation and reflective properties of some alloys of alum- 

 inum with magnesium and with zinc. R. G. Waltenberg and 

 W. W. CoBLENTz. Bur. Standards vSci. Paper 363. Pp. 5, figs. 

 I. 1920. 



This paper gives the manner of preparation and determination of 

 the spectral reflective properties of alloys of aluminum with magnesium 

 and with zinc. 



The reflectivity measurements were made with a spectroradiometer 

 consisting of a mirror spectrometer, a fluorite prism and a vacuum 

 bismuth-silver thermopile. It was found that all of these alloys tar- 

 nish in time and hence are not suitable for mirrors where permanency 

 is of prime importance. The compound of aluminum and magnesium, 

 Al,3Mg4, deteriorates less rapidly than any of the other alloys examined 

 and could be used in apparatus where a highly reflecting mirror is 

 desired for a short time. A reflectivity of 92 per cent at 0.7^1 was 

 obtained with this compound. 



The zinc-aluminum alloy has a minimum of reflectivity at 0.9 /x. 

 An examination of pure zinc disclosed a similar reflectivity minimum at 

 I. oil. R. G. W. 



TECHNOLOGY.— C^m^n/ for spark plugs. Homer F. Staley. 

 Bur. Standards Tech. Paper 155. Pp. 10. 1920. 



The use of cements for sealing electrodes into spark plug porcelains 

 has been found to be attended by serious difficulties in high tempera- 

 ture engines such as airplanes. Among these are: Promotion of 

 oxidation and destruction of the electrode wires by reactions taking 

 place in the cement and between the cement and electrode wires; 

 breaking of spark plug porcelains caused by difference in coefficients 

 of thermal expansion of electrode wires and porcelain; and cracking of 

 cement, with consequent gas leakage, due to the same cause. A cement 

 composed of silicate of soda and raw kaolin has been found to give little 

 trouble from chemical action. In order to avoid the difficulties at- 

 tending the use of any form of cement, the use of a mechanical seal 

 at the top of the porcelain has been tried with promising results. 



H. F. S. 



