276 KIGHTH REPORT — 1838. 



In further corroboration of which may be again noticed M. 

 Payen's own experiment, — that wrought iron locally encrusted 

 with cast iron, by dipping into the hitter while fluid, or pieces of 

 cast iron cast into and surrounded by plates of a different sort 

 of cast iron, are liable to like tubercles, which attach them- 

 selves to the points of contact; reasoning from which, Becquerel 

 rightly concludes, that luant of homogeneity is the cause of this • 

 peculiar action. 



56. M. Payen, as we have seen from his experiments to de- 

 termine the conditions in which white or chilled cast iron would 

 be acted on like the darker- coloured varieties, concludes very 

 erroneously on the practical maxim, that it is much " better to 

 make conduit pipes of white cast iron than any other, as various 

 mineral waters will oxidate it less" — and truly they will so ; 

 but as the peculiar nature of the oxidation in this case stops up 

 the i)ipes at intervals, any amount of uniform corrosion which 

 merely sets a limit to their duration is to be preferred to this, 

 which renders their entire object nugatory. 



57- A letter is found in the Comptes Rendus for 1836, p. 506, 

 from Sir John Herschel, stating that the pipes supplying Cape 

 Town with water had become tubercular ; and that, at his re- 

 commendation, the engineer, Mr. Chisholm, had remedied this 

 by coating the pipes internally with Roman cement. The 

 ancient pipes in the streets of Dublin are likewise much affected 

 in this way ; and some fragments of tlie tubercles, and a piece 

 of the cast iron, which is of the white variety, were presented 

 to the chemical section at Newcastle. 



58. Another method for preventing tubercular cSncretions 

 has been employed successfully by M. Juncker, at Huelgoat 

 mine, in France, viz. that of impregnating the cast iron of 

 which the pipes are made with linseed oil, rendered drying by 

 litharge, and caused to penetrate the pores of the iron l)y great 

 pressure. This fact is confirmatory of a preceding observation 

 I have made, as to the permeability of cast iron to many sub- 

 stances, and seems to offer a new field of investigation, as ii 

 method of protecting cast iron from the action of corroding 

 agents. We know that it has been long usefully applied to 

 other hard and crystallized substances, as stone, marble, &c. 



59. Another method, wholly mechanical, is described in the 

 Mining Review as in use in Cornv/all for the preservation of 

 iron pipes, and must be eminently useful in many cases. 



Each length of pipe is lined with a thin tube of wood, con- 

 sisting of staves of pine, of equal length with the pipe, driven 

 in from the end, and to which the iron pipe forms, as it were, 

 one elongated hoop. The pine staves are driven in when very 



