1843.] on the effects of Sea-water on Iron. 1083 



remedy on this account only is unnecessary, but as a means of lessen- 

 ing ship's expenses with respect to the replacement of iron tanks, 

 which I believe in five years' use are completely worn out, perhaps the 

 anti-corrosive agency of electro-galvanism might in this case be ad- 

 vantageously tried. 



The accumulation of the oxide of iron in the water of the tanks 

 after a long voyage, is certainly excessive ; and to obviate this inconve- 

 nience, I would suggest, that a large filter, of simple construction, should 

 be placed forward for the use of the crew ; to be made of wood in the 

 form of a large box, three feet high, with a breadth from side to side 

 of three feet ; and from before, backwards, one foot and a half should 

 be divided into two compartments by a central division, which should 

 be perforated with a number of small holes to the height of the nine 

 inches from its lower edge, so as to admit of a free passage for water 

 from one compartment to the other. At the bottom of one of these 

 compartments, must be placed layers of sand to a corresponding height 

 with that of the small holes in the division, or nine inches, gradually 

 changing the character of the sand upwards, from fine beach to rough 

 coarse shingle. Let the water to be filtered be poured over this sand, 

 which it immediately percolates, rising on the other side to an equal 

 height, according to a well-known law of Hydraulics, perfectly clear 

 and pure, partaking of all the characters of the best spring water. 

 Thus simply can be procured a daily supply of clean draught water, 

 sufficient for the use of sixty or seventy men. I scarcely need add, 

 that the box would be rendered more water-tight, were it to be lined 

 either with zinc or lead. A small filter upon this principle, but made of 

 slate by Sterling of London, we had on board the Pluto and the Phlege- 

 thon> and its simple construction and efficiency were frequently the 

 subject of remark and admiration. 



As regards iron tanks again, although I do not myself see any great 

 necessity for affording them the protection of electro-galvanism, except 

 to prevent expense, still it would be satisfactory I think to the pro- 

 fession at large, if the following experiment were permitted to be 

 made on a vessel proceeding to sea. It would consist of nothing 

 more than observing the condition of the water contained in two 

 separate tanks, one of which should be brought under the influence of 

 electro-galvanism by being placed in contact with zinc, whilst the 

 other should be in the usual unprotected state. The Captain or 



