INTO THE STRENGTH OF WROUGHT-IRON PLATES. 
711 
under circumstances exceedingly difficult to explain. This is an investigation not 
unworthy the attention of some of our best chemists, to whom the causes may be 
known, but which are at present, as far as 1 know, unaccounted for. For example, 
I may mention that an iron ship, if kept constantly in use, or nearly so, will last 
for a number of years exposed to all the changes of weather and temperature without 
any sensible appearance of decay. The same may be said of iron rails, over which 
are passing daily such enormous weights, and at such velocities as almost to neu- 
tralize the action of the elements. All these are striking examples of the durability 
of wrought iron, which may be considered as an important element of its security, 
and a recommendation for its extended application. There is another circumstance 
in connection with this subject to which it may be necessary in this place to advert, 
and that is the effect which a long continuance in salt water has upon the hull of an 
iron ship. It is well known that a long immersion of cast iron in the sea will con- 
vert it into plumbago, and that a similar process with malleable iron, from its contact 
with the saline particles of the ocean, produces oxidation ; and in case the immersions 
were long continued, the effects of this destructive process might endanger the safety 
of the ship. As yet we have not had sufficient evidence of its effects to enable us to 
come to any definite conclusion, but it is not improbable that an occasional visit to 
harbours of fresh water may mitigate, if it does not entirely neutralize, the inju- 
rious effects which the material is likely to sustain. With these observations, which 
I offer with diffidence, I now beg to direct attention to the abstracts as deduced from 
the experiments. 
Abstract of Results as obtained from the experiments. 
In Part I. of this inquiry we have endeavoured to show that 50,000 lbs. per square 
inch is the mean breaking weight of iron plates, whether torn asunder in the direc- 
tion of the fibre or across it ; and we have also shown that the tensile strength of 
different kinds of timber drawn in the direction of the fibre varies in a given ratio to 
that of iron : the timber in this comparison being represented by unity, we have the 
following ratio of strength : — 
Ash as . . 
Timber : 
. . . 1 : 
Iron. 
2-94 
Teak as 
. . . 1 : 
3-33 
Fir as . . 
. . . 1 : 
4*16 
Beech as . 
. . . 1 ; 
4-34 
Oak as . . 
. . . 1 : 
o'OO 
These, for practical purposes, may be taken as a fair measure of the strength of the 
different woods as compared with that of iron plates. 
It has been shown that wrought-iron plates, when riveted together, lose a consi- 
derable portion of their strength, as may be seen by the experiments in Part IV., where 
the plates, by their union with each other, lose by the ordinary process of riveting 
44 per cent., and by the best mode of riveting 30 per cent. This should not however 
