10 REPORT—1843. 
uniform in texture, but proved, on subsequent chemical examination, to be 
most free from any foreign matter, consisting in fact of nothing besides iron, 
except a mere trace of carbon and silex. My former presumption (64) in 
favour of rolled bars is therefore partly erroneous. 
Next to this in durability stands Low Moor Boiler Plate, an iron whose 
purity and excellence is universally known. These results make it plain that 
for iron ship-building the-two latter kinds of iron are greatly to be preferred, 
and whether in clear or foul sea water, or in fresh or exposed to wet and dry, 
are very superior to common Staffordshire plates for this purpose. 
The iron of which the faggoted bar (a 14) was formed, was best Stafford- 
shire rivet iron of excellent quality. Comparing the results of the corrosion 
of the Dannemora Swedish iron with this, it is apparent that no superior 
durability is imparted by the Swedish method of refining over that obtained 
by our own puddling process, when properly conducted. 
313. In Table XLV. the average results for all the wrought irons of most 
practical importance are given in each condition of experiment ; those for the 
remaining sorts may be easily calculated from the previous tables. 
314. Foul water, z.e. that evolving sulphuretted hydrogen, and other gases 
resulting from putrifying organic matter, acts, whether salt or fresh, much 
more powerfully upon wrought iron than when free from such impurities. 
The actual contact of soft putrid mud beneath salt water appears to be more 
destructive than the water itself. 
315. In the autumn of the year 1832, I observed that small gas bubbles 
were constantly evolved from the mud at the bottom of some of the lagunes 
at Venice, which on reaching the surface became instantly luminous, and 
disappeared with, as far as could be judged, a real combustion. 
The gas when collected, however, was not spontaneously combustible, and 
I had no means of examining it with precision. 
It seems probable, however, that when large quantities of animal matter 
are in a state of decomposition, phosphorus in some of its combinations will 
always be found; and when iron is exposed under such conditions, a phos- 
phate of iron is produced. This has actually been observed in the case of a 
large quantity of iron weapons discovered a year or two ago in a bog near © 
Dunshaughlin, county Meath, along with a mass of bones of oxen, horses and 
other animals. The surface of most of the iron, which, after the lapse of 
some centuries, during which it was enveloped in damp peat, was in singu- 
larly good preservation, was almost uniformly covered with a bluish coat of 
phosphate of iron, quite similar apparently to the native blue phosphate. 
316. Proceeding now to the experiments made 
On Steel, 
the results of which are given in the same tables with the wrought iron, we 
find that in general steel corrodes much more uniformly and a good deal more 
slowly than wrought iron. 
That hardened cast steel, after “tilting,” has the average minimum cor- 
rosion, and that low shear steel, which is in fact a sort of steely iron, has the 
maximum. 
317. It was stated before (1st Rep.21) that plumbago occasionally had been 
found from the action of air and water on wrought iron, as well as on cast 
iron. The present results show that raw or untilted cast steel always produces 
a brilliant shining plumbago like that from white cast iron, and in general 
that the production of plumbago by aqueous corrosion is dependent (so far 
as the metal is concerned), either in cast or wrought iron, upon the amount 
of combined carbon, and upon the state of aggregation of the particles of the 
