274 KIGHTH REPORT 1838. 



which supply Grenoble with water (presently to be described) 

 are formed in tliis way, the waters which pass in them having a 

 feeble alkaline reaction, owing to the presence of carbonate of 

 lime, and being slightly saline. 



"At the suggestion of the Commission, M. Payen incrusted 

 pieces of wrouglit iron in cast iron, and fragments of cast iron 

 in plates of cast iron of another sort : in all these cases he found- 

 the tubercular oxidations adhered to the points of contact. 



" It may be concluded (they continue), from the observed 

 facts, that whenever there is a want of homogeneity in cast-iron 

 pipes, which convey water slightly alkaline and saline, tubercles 

 will be formed at the points where heterogeneity exists. M. 

 Payen has studied the circumstances in which, as regards the 

 formation of tubercles, white cast iron produces the same effect 

 as gray or black;" having diluted one volume of a solution of 

 carbonate of soda and of chloride of sodium, saturated at a 

 temperature of 15° Cent., with from 100 to 200 volumes of 

 distilled water, he has found that all the solutions between 

 these limits produce on white cast iron oxidations evidentlj'- 

 more tubercular and better localized than on the other kinds of 

 cast iron. These last afford more points of easy attack, and 

 produce more numerous tubercles, and hence less distinct. 



" We see, then, that white cast iron, as being less oxidizable 

 by certain mineral waters, appears to merit the preference over 

 gray iron for water-pipes." 



The reporters further add, " We are not obliged to say that 

 the constitution and composition of the artificial tubercles are 

 the same as those of the pipes at Grenoble, which would tend to 

 prove that both depend on like causes." 



51. This local action, in many cases, is of small importance, 

 and indeed might be more advantageous than that deep removal 

 of metal which takes place in softer irons ; but in the case of 

 pipes or similar receptacles for the containing or conveying of 

 water, the accumulation of these tubercular excrescences gradu- 

 ally chokes the passages at numberless places, and obliges the 

 removal of the whole conduit. Nor does this evil solely apply 

 to chilled cast iron ; all hard cast iron which has been rapidly 

 or unequally cooled is pro iatifo liable to the same. 



52. M. Vicat, in the Comptes Rendiis, vol. iii. 1836, p. 181, 

 gives an account of the formation of these tubercles on the pipes 

 which supply Grenoble with water, in which they had increased 

 to such an extent as seriously to reduce the delivery of water, 

 and engaged the attention of the authorities. He proposed as 

 a remedy the coating of the pipes inside with hydraulic mortar 

 to the thickness of 2i millimeters, — in fact, to brush them over 



