364 POPULAR LECTURES AND ADDRESSES. 



pensive that the cost of that mode of keeping 

 the wire from corrosion was not worth speaking of. 

 There is, however, a good deal of trouble con- 

 nected with it ; but it must be remembered that 

 that trouble would not be much regarded on 

 board a ship appointed especially for making 

 soundings. The preserving effect of alkali upon 

 steel is well known to chemists. It seems to be 

 due to the alkali neutralising the carbonic acid in 

 water, for the presence of carbonic acid in water is 

 the great cause of iron being corroded. The fact 

 is well established that iron would remain perfectly 

 bright in sea-water rendered alkaline by a little 

 quick-lime. Caustic soda is a more sure material, 

 because with it we can make more certain that the 

 water is really alkaline. I am told by a very 

 excellent authority Mr. James Young, that, 

 whether caustic soda or quick-lime is used, all 

 that is necessary, in order to make sure that the 

 pickle will be a thorough preserver of the wire is 

 that it should be found to be alkaline when tested 

 with the ordinary litmus test-paper. The American 

 experience is, that although the caustic soda 



