186 lilK ROYAL SOCIETY OF CANADA 



brownish-red rust appeared. This is popularly known as the "red 

 water trouble." However, it must be noted that our figures indicate 

 that the actual amounts of iron corioded were the same for treated 

 and raw waters. ApjDarently the state assumed by the iron corroded 

 from the metal is a much more important question from the stand- 

 point of a city supply than the actual amounts. The conclusion in 

 this connection is that the so-called mechanical treatment of water is 

 very liable to bring about some discoloration. 



In all these experiments it was noted that raising the temperature 

 greatly accelerated corrosion. 



Corrosion of Metals in Contact. 



In the experiments on metals in contact, corrosion of iron alone 

 was first determined. The effect of contact with aluminium is to 

 diminish the corrosion of the iron, the degree of corrosion decreasing 

 with the rise of temperature. As might be expected the effect of 

 contact with copper is the reverse of that with aluminium, corrosion of 

 the iron being greater at ordinary temperatures as well as at higher 

 temperatures. On the same methods being employed, replacing the 

 iron with lead, we find the effect of the aluminium much less marked, 

 but nevertheless in the same direction, the contact of the aluminium 

 decreasing the corrosion of the lead. On the other hand, the effect 

 of copper is to enormously increase the corrosion of the lead. A ref- 

 erence to the figures would be very interesting. For illustration, we 

 have them roughly plotted in the accompanying diagram. 



In this diagram we have located each line by only two points 

 and consequently it is not strictly correct to make a straight line. 

 It would indeed be interesting to definitely trace these lines, 

 especially in that direction towards which they meet and cross. 



The great difference of potential between copper and aluminium 

 sets up an active attack on this somewhat inert metal, covering it 

 with a gelatinous hydrate AljCOH)^. Another interesting point 

 noted was that on some of the bottles there were heav}'- precipitates 

 of silica (SiOa) — products of attack of the glass, which perhaps 

 acted also to set up a potential difference. 



Incidentally, in the course of the work certain interesting ob- 

 servations were made which may be briefly recorded. It is interesting 

 to note that boiled distilled water has little or no effect on iron; this 

 is accounted for by the fact that the conductivity of such water is 

 very low — i.e., there are very few hydrogen ions in solution. A curious 

 fact is revealed in one experiment, where it is seen that the corrosion 

 at 50° C. is much greater than at 60° C. Most of these wires carried 



