ACTION OF WATER OX IRON. 297 



was lined. The bolt or pin for connecting the valve to the cy- 

 linder is of wrought iron, which, as well as the cast iron, was 

 found in a perfect state. I have also sent a piece of a cast-iron 

 clough paddle, taken out of one of the dock sluices. When 

 first taken up it was quite in a soft state, capable of being easily- 

 cut with a knife] but by exposure to the atmosphere has again 

 become hard. 



" I am, Sir, your obedient servant, 



" Gilbert Cummins. 

 " To Mr. Rohert Mallet." 



With this fragment, weighing only about 500 grains, we made 

 a few experiments, and shortly vi'rote again to Mr. Cummins, 

 requesting a larger supply of the brass, and replies to certain 

 questions respecting its influence, as in annexed copy: — 



''Mr. Gilbert Cummins, 



"Sir, — In reply to yours of the 23rd instant, Professor Davy 

 and myself return you our thanks for your attention, and for 

 the specimens of altered cast iron and the brass, &c. just re- 

 ceived. The specimen of brass is quite sufficient to enable us 

 to determine its composition, but insufficient to enable us to 

 institute some comparative experiments as to the precise condi- 

 tions of its preservative power. For this purpose it would be 

 necessary to have five or six pomids of the brass, the value of 

 which, should that stand in the way, we are quite ready to pay; 

 we therefore hope to receive it by the same conveyance which 

 brought the former specimens. We M'ould also desire replies 

 to the following questions in yoiu* next — 



" 1st. Is the brass — brass proper or gun metal, viz. — made 

 with zinc or tin, and what, about, are its proportions ? 



" 2nd. How long has it been in use as a preserver of cast 

 iron, and to what purposes chiefly applied ? 



" 3rd. How has the brass been chiefly applied ? has it been 

 cast into or round the cast iron preserved, at a temperature of 

 fusion, or merely placed in contact at a common temperature ? 



" 4tli . Have its preservative effects been uniform, or have thei'e 

 been exceptions, and if so, under what conditions ? 



" 5th. Has its preservative influence been found as effective 

 when the iron Avas exposed to 'wet and dry,' or about the level 

 of ordinary spring tides, as when ahvays immersed in sea \vater? 



" 6th. Has cast iron in the neighbourhood of the brass, but 

 not actually shielded or covered up from the sea water, been as 

 well protected as when covered ; for instance, would the pin of 

 a hinge in a brass socket be better protected than the parts of 

 the iron hinge outside the socket ? 



