ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 255 



water. The presence of sodium in the water could not be detected until 

 ten hours after ; in 24 hours, the flame test gave a well marked 

 indication. Similar results were obtained when potassium hydrate 

 solution was used instead of sodium hydrate. Plates of iron which had 

 been "pickled" in sulphuric acid, washed and dried, were found to 

 corrode more rapidly than plates not so treated. The more rapid 

 corrosion was apparently due to retention of acid in the pores of the 

 metal, It is suggested that the passivity of iron induced by immersion 

 in alkaline solutions is due to the retention of minute quantities of the 

 solution in the pores of the iron. It is probable that there are more 

 kinds of passivity than one. 



Magnetic Properties of Heusler Alloys.* — An account is given of 

 several researches carried out upon the magnetic copper-manganese- 

 aluminium alloys. E. B. Stephenson found that the alloys had melting 

 points between 910° and 970° C, and gave cooling curves characteristic 

 of solid solutions. Transformation points were observed at 615° C. No 

 relation was established between microstructure and magnetic properties. 

 E. Take studied the effect of heat-treatment upon the magnetic pro- 

 perties of alloys containing about 17 p.c. manganese and 9 p.c. aluminium. 

 A. A. Knowlton also investigated the effect of heat-treatment of similar 

 alloys, and studied their microstructure. 



Annealing of Metals.f — Matweeff has determined the hardness of 

 zinc, aluminium, copper, silver, brass, and aluminium l)rouze, hardened 

 as much as possible by cold work, and annealed for stated lengths of 

 time at different temperatures. The Brinell method was used, with a 

 glass ball one millimetre in diameter. It was established that the cold- 

 worked pure metals did not begin to diminish in hardness until a certain 

 well-defined temperature was exceeded, 100° C. for zinc, ;-)00" C. for 

 copper and silver, ;ri50' C. for aluminium. A great fall in hardness then 

 took place, and was completed in a small range of temperature. The 

 presence of other elements forming alloys modified the hardness of the 

 annealed specimen, and the temperature at which softening l»egan, and 

 increased the range of temperature within which annealing proceeded. 



Cementation of Iron by Solid Carbon. |—G. (Uiarpy and S. 

 Bonnerot have investigated this question further. Graphite and mild 

 steel were maintained in close contact by high compression mechanically 

 applied, and were heated a little above 950° C. for times varying from 

 10 to :>8 hours in six different experiments, the gas pressure varying 

 from 0"01 to 1*5 mm. of mercury. About one-third of the minute 

 amount of gas present was carbon monoxide. In the high vacua no 

 cementation occurred, but when the pressure rose above (V5 mm. 

 mercury, cementtition was ol)served. With pressures 1*0 to 1*5 mm. 

 patches of easily recognized pearUte were produced, and the carbon 

 content of the steel rose to 0*5 per cent. The authors conclude that 

 in the complete absence of gas, no cementation whatever of iron by 

 solid carbon can take place at 950" C. 



* Engineering, xcii. (1911) p. 739. 



t Rev. Metallurgie, viii. (1911) pp. 708-16 (13 figs.). 



X Comptes Rendus, cliii. (1911) pp. 671-3. 



