18 REPORT—1843. 
injurious effects of brass depend much upon the relative proportions of its 
constituent metals, and by a proper choice in this respect may be made very 
small. (See Tables, 2nd Rep. IX. and X., and 3rd Rep, XI. and XII.) Brass 
or the alloys of copper and zinc, are to be preferred to gun-metal or those of 
copper and tin, all of which greatly promote the corrosion of iron when in 
contact with them in a menstruum. 
342. It is a good palliative when copper or brass must be in contact with 
the iron, as in the flanges of sea-cocks, &c. in steam-vessels, to interpose a 
thickness of patent felt, saturated in boiled coal-tar or in wax, or other non- » 
conducting substance ; no interposition of “short iron pipes” or other metallic 
matters, unless masses of zine, will be of any use; and the effect of local 
corrosion thus produced, especially about the engine-room and boilers in 
iron steamers, demands the most scrupulous caution, much more than ap- 
pears yet to have been given it, gun-metal sea-cocks, copper blow-off pipes, 
&e. being at present in general attached directly to the iron hull, which are 
certain soon to cause the iron plate round them to be eaten away, and thus 
the vessel is rendered leaky in a vital point and probably at an unexpected 
moment. The application of a thick zine flange outside the ship’s side or 
bottom, at the junction of such a cock or pipe, would be a remedy, but would 
promote fouling; increased local scantling, and non-conducting flanges be-~ 
tween the electro-negative metal and the iron, are most to be commended. 
343. There are several substances found in commerce, the contact of which 
with the iron of ships, when carried as loose cargo, is more or less injurious, 
and unless an effective method of protection be adopted, such articles should 
not be taken in iron vessels but at commensurate freights ; some of these may 
be named, as pyritose wet coal, sulphur, sulphur stone, gypsum, galena, 
copper ore, or other metallic sulphurets, when wet; alum, salt, bleaching 
salts; acids of all sorts, when not rendered secure against escape; wet bark 
for tanning, or other matters containing gallic or tannic acids, &c. 
344. The following extract from our Tables gives the relative values of 
several of the principal sorts of wrought iron and steel found in commerce, 
in respect to durability in clear sea water; their relative rates of corrosion are 
directly as the numbers attached to each, and hence the values of the several 
sorts of iron, &c. for ship-building are inversely ly as those numbers. 
Make of Iron. Inverse Relative Value. 
Common Shropshire bar. . . . - . + . « . 36°14 
Tilted castiron . . ESTE AD CS MRT LO OME ASE RSS 
Cold short bar, Staffordshire SMA 2 Bt Da eS TRA A 
BHeRP RESET, Bit PARTI I Cie Gohan eat a Ole 
Best bar iron, Bradley. . . .. . Ras Fea 
Spring steel, tempered . . . 2. 2. 2 1 2... « T1861 
Blister steel, soft. . . J opdag Oly Si ee 
Best bars and plates, Doulais (hot blast) 2) AA fe Te eee 
Swedish iron, Dannemora . . Pl RA ae a so 
Red short bar, Staffordshire . . . . . . . . . 10°78 
Common plates, Banks. . 2... 2. . 1 ss. 10°60 
Common Shropshire bar, case hardened ... . . . 10°14 
Best plates and bars, Forest of Dean . . . . . . 10:08 
Cast steel, as hard as possible. PJ! ORT See 
Best bars and plates, Doulais ta blast) oe) Yee SO ea 
Low Moor plates. . . . ae LU, PL 
Best faggoted scrapiron . . . . . . « . ss) D252 
From the foregoing table it is obvious that. plates rolled from scrapped iron 
