250 Dr Davy on the Incrustation 



order once flourished in close proximity to each other in 

 a territory which now forms part of England. — Professor 

 Orven's History of British Fossil Beptiles^ Part iii., p. 132. 



On the Incrustation which forms in the Boilers of Steam- En- 

 gines, from a Letter addressed to Dr G. WiLSON, F.R.S.E. 

 By John Davy, M.D., F.R.S., Inspector- General of Army 

 Hospitals. Communicated by the Author.* 



On entering on this inquiry, which I did after my return from 

 the West Indies in December 1848, and after communicating a short 

 paper to the Royal Society " On Carbonate of Lime in Sea-water," 

 it appeared to me desirable to collect as many specimens as possible 

 of incrustations from the boilers of steam-vessels, now so widely em- 

 ployed in home and distant navigation. By application to companies 

 and to friends in our sea-ports, as Dundee, Hull, Southampton, Hayle, 

 Liverpool, Whitehaven, I have succeeded in procuring specimens of 

 incrustation formed by deposition in voyages from port to port, in 

 the British and Irish Channels and the North Sea, between South- 

 ampton and Gibraltar, in the Mediterranean and the Black Sea, and 

 •in the Atlantic Ocean, between Liverpool and North America, and 

 between Southampton and the West Indies. I am promised speci- 

 mens from the Bed Sea and the Indian Ocean, — but these I have 

 not yet received. 



The character and composition of the incrustation, whether 

 formed from deposition from water of narrow seas or of the 

 ocean, I have found very similar — with few exceptions, crystal- 

 line in structure, and, without any exception, composed chiefly of 

 sulphate of lime ; so much so, indeed, that unless chemically viewed, 

 the other ingredients may be held to be of little moment, rarely 

 amounting to five per cent, of the whole. From two specimens of 

 incrustation from the boilers of steamers crossing the Atlantic, one 

 of which you sent me, in which you had detected a notable portion 

 of fluorine, judging from its etching effect on glass, — I also procured 

 it, it was in combination with silica ; and procured it also so com- 

 bined from two obtained from steamers navigating our own seas, one 

 between Dundee and London, the other between Whitehaven and 

 Liverpool. Of this I had proof, by covering with a portion of glass 

 or platina foil a leaden vessel charged with about 200 grains of the 

 incrustation mixed with sulphuric acid, and by keeping the glass cool 

 by evaporation of water from its surface, and by supplying moisture 

 for the condensation of the silicated gas by a wet band round the 

 mouth of the vessel. After about twenty-four hours under this pro- 

 cess, a slight but distinct deposition was found to have taken place, 



* Read to the Meeting of the British Association at Edinburgh, 1850. 



