342 SECTIONAL TRANSACTIONS.— A. 



with many batches of material, the mechanical strength was so much reduced 

 that large quantities of parts were scrapped during the assembly stages. 



Investigations conducted, involving raw materials, heating and cooling 

 rates, different soaking times and maximum temperatures, machining 

 conditions, etc., proved that the magnetic degradation was due to nitriding 

 caused by free ammonia, order of 0-5 per cent., in the cracked ammonia 

 inert atmosphere. A purifier in the gas track eliminated the trouble. 



The high magnetic properties of pure ferrite desired, tend to encourage 

 mechanical weakness by large grain structure and elimination of inter grain. 

 Dry hydrogen inert atmosphere has no effect, but H-H2O gas penetrates 

 the iron, reduces the iron carbide cementing medium, lowers elongation, 

 increases brittleness and leaves tensile strength almost unaffected. Marked 

 eflFects in practice occurred below 0-03 per cent. Controlled carburising 

 gas admitted into the H atmosphere to balance reducing and oxidising 

 effects eliminated the trouble and allowed the recovery of spoiled parts. 



Miss M. D. Waller. — Chladni designs produced by means of solid carbon 

 dioxide (11.45). 



Loud notes may be produced from metal objects by touching them with 

 solid carbon dioxide. {Report British Association, p. 314, 1932; Proc. 

 Phys. Soc. 45, loi, 1933 ; Nature, 135, 475, I935-) This new method of 

 producing vibrations has now been used to make a large number of Chladni 

 designs and also to study the resonances of bodies of irregular shape. The 

 value of the method depends upon the fact that the solid carbon dioxide 

 can be applied to any point of the surface and is very vigorous in its action 

 The frequencies of the vibrations excited lie between about 1,000 and 

 4,000 c.p.s. 



f 

 Dr. H. A. Stevenson. — The prevention of steamy shop windows (12.0). 



A description is given of an experimental shop-window which was built 

 to investigate methods for preventing steamy windows. The apparatus 

 used and the method of experimental procedure are also described. 



Various methods for preventing steamy shop-windows are discussed from 

 the theoretical and from the practical aspect. The most practicable of 

 these methods — ventilation with air from the street — was examined in 

 detail. 



Natural ventilation proved to be effective but difficulty was experienced 

 m securing adequate ventilation in actual shop practice. 



Fan ventilation was found to be entirely satisfactory. All the desirable 

 features of natural ventilation can be attained together with additional 

 advantages, such as a greater rate of ventilation and a greater flexibility in 

 the construction of the ventilating system. 



Prof. J. Satterly. — The recent development of everyday physics and its 

 application to Canadian life (12.15). 



Refrigeration. — Canada is so large that meats, vegetables, fruits, fish, have 

 to be refrigerated for home transportation. 



Owing to the long winter and backward spring, early vegetables and fruits 

 are imported and refrigerated from the countries to the South. The house- 

 wife also needs a refrigerator both in winter and in summer. Use of ' dry 



