X907.] MASON— ACTION OF WATER UPON METALS. 113 



is also called therein to the fact that moorland streams are highest 

 in acidity during wet weather because of drainage from peaty 

 surface sources and less so during periods of no rain on account 

 of their supply at such seasons coming from the flow of springs. 



In this connection it may be noted that H. W. Clark observed 

 that carbonic acid in a soft water was the main factor that caused 

 lead to be taken into solution by the waters of Massachusetts.^ 



It is by no means new to distinguish between the " solution " of 

 lead and that " erosion " of the metal which some waters exercise 

 whereby insoluble lead salts are formed with appreciable increase 

 in the turbidity of the water. 



Such classification of the action upon lead has been developed 

 by the report of the London Local Government Board with great 

 care. 



For our purposes it will suffice to note that '' erosion " does 

 not occur in the absence of oxygen, and we are also to remember 

 that from the sanitarian's point of view " erosion " may be fully 

 as objectionable as " solution " if no opportunity for clarification 

 be furnished. In fact, the former may readily be the greater evil 

 of the two, because of its involving the possibility of the ingestion 

 of large quantities of lead salts held in suspension. 



Piping water in tubes of galvanized iron is very common, and 

 as zinc is often more easily attacked than lead it is pertinent to 

 ask if it be equally dangerous. So far as our present experience 

 can guide us towards a correct solution of this question, the reply 

 must be a negative one and the following opinions are presented 

 in support of such contention : 



In the journal of the German Society of Gas and Water Engi- 

 neers for 1887 H. Bante collected statistics to show '' that the use 

 of galvanized pipes should be in no way detrimental to health." 



Similar views are entertained by \^ Ehmann, director of the 

 water supply of Wurtemberg.- 



According to Thresh^ '' There is no doubt that waters contain- 

 ing traces of zinc are used continuously for long periods without 



' Engineering Nczvs, Dec. i, 1904. 



2/. Fk. Inst., Nov., 1890. 



3 Examination of Waters and Water Supplies, p. 85. 



