PRESERVATION OF IRON. 379 



the same effect will be produced by placing them in the bath 

 heated and maintained at a temperature of about 300 Fahr., 

 and allowing them to remain therein for some time after they 

 have become as hot as the tar." 1 



In both these methods, as described in Dr. Angus Smith's 

 specification, the essentials are absolutely clean surfaces, and a 

 high temperature, but of the two that requiring the heating of 

 the castings before immersion was evidently regarded by the 

 inventor as the most efficient. 



A thin coating or film of mud, and the adhesion of marine 

 growths, such as weeds and shell-fish, by which the surface of the 

 immersed iron is secured from contact with fresh supplies of water, 

 have a considerable effect in preserving the surface from corrosion. 



An examination as to the condition of the iron piles in the 

 South Bassien Bridge, on the Bombay, Baroda, and Central 

 India Railway, led to the conclusion that the greatest corrosion 

 in cast-iron piles exists close to low water, and does not extend 

 to any considerable depth below it, a conclusion which also 

 applies to bolts and braces. After an exposure of twenty-five 

 years in a salt-water tideway, the piles were found to be in a 

 very good condition, and corrosion had only occurred in places 

 which were easily accessible for repairs and renewals. 



Average composition of sea-water salts : 2 



Per cent. Per cent. 



Chloride of sodium 77*758 77*758 



Chloride of magnesium 10-878) 



Sulphate of 4-737J 15-832 



Bromide of' 0-217) 



Sulphate of potash 2-465 2-465 



Carbonate of lime 0'345\ Q ac 



Sulphate of 3-600/ 



100-000 100 000 



Analysis of sea- water : 3 



" Per cent. 



Chloride of sodium 2*7254 



Chloride of magnesium 0*3813 



Sulphate of 01660 



Bromide of 0-0076 



Sulphate of lime 0*1262 



Sulphate of potash 0-0863 



Carbonate of lime 00120 



3-5040 



Water 96*4960 



100*0000 



Fixing Bolts in Masonry. 4 In connection with the securing of 



1 Dr. Angus Smith's Specification, Xo 12291, 1848. Printed 1857. 



2 Pro. Royal Soc. Edinburgh, Sessions 1889-90, p. 102. 8 Ibid., p. 103. 

 4 Scientific American, vol. Ixiii. p. 184. 



