ACTION OF WATKR ON IRON. 287 



tion by boiling of the saline contents of sea water, and the re- 

 spective temperatures at which each salt deposits, sliowing that 

 they fall in the order of their respective insolubilities, indicate 

 that important differences in the corrosive action of sea water, 

 when boiling, may result from its degree of saline concentra- 

 tion, and to this, the resulting boiling point, the electro-con- 

 ducting power of the fluid, as well as the nature of the salts 

 deposited and remaining in solution, are conditions. And, fur- 

 ther, as means have been devised (although with increased ex- 

 penditure of fuel) of preserving sea water in marine steam 

 boilers, (or others using salt water,) at a constant degree of sa- 

 turation, it becomes important to discover when this is such as 

 to produce a minimum corrosion, whether before or after the 

 deposition of the sulphate lime, or of the chloride, sodium or 

 magnesium. 



79. The next box, No. 4, has been moored by permission and 

 assistance of the Ballast Corporation of the port of Dublin, in 

 the foulest water of the river Liffey, in the mid stream, opposite 

 the mouth of the Poddle river, at this place a tributary of cor- 

 rupted water. It lies in water 4 feet deep at ebb, and from 15 

 to 20 feet at flood tides. The water is very brackish at full 

 tide, and at the other periods fi-esh ; its temperature, when the 

 box was sunk, was 61° Fahr. The specimens in this are the 

 same as in Nos. 2 and 3, as may be seen by the tables. Its ob- 

 ject will be to determine the relative effects of foul river water, 

 alternately brackish and fresh, and this will again compare with 

 the results to be obtained from the last box, No. 5. 



80. It has been sunk in the clear, unpolluted fresh water of 

 the Liffey above Island-bridge, and within the premises of the 

 Royal Military Hospital. It lies in water varying at times from 

 3 feet to 6 feet in depth ; its temperature varies with the season. 



Specimens of water have been taken from these five localities 

 for examination, and vvill be again taken and examined from 

 time to time. The highest and lowest temperatures of each 

 will also be observed. 



81. In each of these boxes have been included a number of 

 specimens, coated with various protecting varnishes and paints. 

 — This was originally suggested by a fact of importance commu- 

 nicated to the writer by Thomas Rhodes, Esq., civil engineer, 

 whose experience in the construction of great works in iron is 

 well known. He mentioned, that when engaged on the locks 

 of the Caledonian canal, certain cast-iron sluices were put down 

 and exposed to the ocean water, having been coated over with 

 common Swedish tar, with the exception of their faces, 

 which were ground together, and were removed in about four 



