1068 Experiments and Papers, f No. 144. 



month, but if it be deemed emergently requisite, I will endeavour, 

 at any inconvenience, to comply with the Board's wishes. 

 Calcutta, 3\st August, 1841. I have, &c. 



(Signed) W. B. O'Shaughnessy, 



Chemical Examiner. 

 Fort William, Marine Superintendent's Office, 

 the 23d Sept 1843. (True Copy.) 



(Signed) C. B. Greenlaw, Secretary. 



C. B. Greenlaw, Esq. Secretary to the Marine Board. 



Sir, — In continuation of a previous letter, I have the honor to re- 

 sume the subject of the corrosion of Sea-going Iron Vessels, and the 

 best means of its prevention. 



2d. There exists no material difference in the constitution of the 

 several waters you forwarded to me for analysis, or which I received 

 from time to time from other sources, beyond a variable degree of dilu- 

 tion with fresh water from the influence of the tides. 



3d. The object of my experiments, was to ascertain the comparative 

 rate of corrosion effected by the waters of Saugor, the Bay of Bengal, 

 and Kyook Phoo, the nature of the corrosion, and the best means of its 

 prevention. 



Rate of Corrosion. 



4th. For the first object, pieces of sheet iron of six inches long, three 

 broad, and accurately weighed, were immersed in the water in glass 

 vessels, slightly covered to check evaporation, any loss from this cause 

 being made up by rain water from time to time. The result of very 

 numerous experiments conducted on this plan, is, that the rate of corro- 

 sion is exactly the same in all the waters under experiment, in a period 

 of six months, being as nearly as possible 5 grains loss from each super- 

 ficial foot daily. 



5th. The influence of size of the plates was examined as far as op- 

 portunities permitted, by arranging sets of iron sheets, all in metallic 

 contact, in the manner shewn in the accompanying diagram.* From 



* The sheets of iron being merely arranged vertically, it has not been thought 

 necessary to add the diagram. 



