THE CORROSION OF IRON AND OTHER METALS 333 



in the case of alloys containing such an " excess " of zinc that 

 we must contemplate separate attack on the zinc as possible. 

 No doubt the electro-negative impurities in brass play an all- 

 important part in localising the attack but we have yet to learn 

 the manner in which changes in the mechanical and crystalline 

 structure of alloys affect corrosion. An interesting illustration 

 of the mariner in which impurities act was brought under the 

 notice of the Institute of Metals recently by Prof. H. Louis, 

 who traces the failure of a brazed joint to the presence in the 

 braze of a fine network of an alloy probably of tin with lead, 

 the planes thus formed being planes of weakness liable to yield 

 under strain, thus allowing liquids to penetrate into the mass 

 of the metal. 



A question of special importance was raised by the corre- 

 spondence in the Engineer in the year 1907 on the behaviour 

 of Muntz metal in Australian water. It was then stated that 

 this alloy has undergone corrosion more rapidly of late years, 

 since it has been customary to make it from electrolytic copper 

 instead of from that prepared by the old poling process. It is 

 difficult to associate the idea of protection with the presence 

 of impurities, unless it be that they affect the mechanical 

 crystalline structure of the alloy in an advantageous manner. 

 It is not impossible that electrolytic copper may be richer in 

 cuprous oxide than polled copper and it is conceivable that this 

 oxide may play an important part in facilitating the corrosion 

 of copper. 



In too many cases probably the deterioration which brass 

 condensers suffer in use is due to careless working, especially to 

 neglect to cleanse them properly when they are put out of use. 

 On this account the final conclusion in the recent communication 

 made by Mr. Bruhl to the Institute of Metals is probably that 

 most worthy of attention — viz. " That the tubes should be 

 flushed with clean water after use " ! This communication, it 

 may be added, carries the subject very little further. Mr. Bruhl 

 evidently stands on an elementary footing, as he is in no way 

 clear even why the presence of acid should be essential to the 

 occurrence of corrosion. And yet he treats learnedly of the 

 nature of corrosion in the usual stilted ionic style ; but the sub- 

 ject is merely a hot potato picked up by the way and fortunately 

 as soon dropped. A perfect gem of information is provided in 

 this section, however, by the representation of the influence of 



