THE ROYAL ARTILLERY INSTITUTION. 
145 
(60) The amount of heat developed is considerable when the specimen is 
suddenly stretched, as shown in the formation of vapour from the melting of 
the layer of ice on one of the specimens, and also by the surface of others 
assuming tints of various shades of blue and orange, not only in steel, but 
also, although in a less marked degree, in iron. 
(61) The specific gravity is found generally to indicate pretty correctly 
the quality of specimens. 
(62) The density of iron is decreased by the process of wire-drawing, and 
by the similar process of cold-rolling, instead of increasedj as previously 
imagined. 
(63) The density in some descriptions of iron is also decreased by additional 
hot-rolling in the ordinary way; in others the density is very slightly 
increased. 
(64) The density of iron is decreased by being drawn out under a tensile 
strain, instead of increased as believed by some. 
(65) The most highly converted steel does not, as some may suppose, 
possess the greater density. 
(66) In cast-steel the density is much greater than in puddled steel, which 
is even less than in some of the superior descriptions of wrought-iron. 
The following remarks are also worthy of notice. 
“ The breaking strain per square inch of wrought-iron is generally stated 
to be about twenty-five tons for bars and twenty tons for plates. This 
corresponds very nearly with the results of the writer's experiments, of which 
the following table presents a condensed summary :— 
lbs. 
lbs. 
lbs. 
tons. 
188 bars rolled . 
highest 68,848, 
lowest 44,584, 
mean 
57,555 
= 25f 
72 angle iron, &c. 
do 
63,715, 
do 
37,909, 
do 
54,729 
= 24| 
167 plates, lengthways, 
do 
62,544, 
do 
37,474, 
do 
60,7371 
= 21f 
160 plates, crossways, 
do 
60,756, 
do 
32,450, 
do 
46,171> 
“ Although the breaking strain is generally assumed to be about 25 tons 
for bars and 20 tons for plates, very great difference of opinion exists as to 
the amount of working strain, or the load which can with safety be applied 
in actual practice. The latter is variously stated at from a third to a tenth. 
It will be observed that whilst much discussion has arisen as to the amount 
of working strain, or the ratio the load should bear to that of the breaking 
strain, the important circumstance of the quality of the iron, as influencing 
the working strain, has been overlooked. The Board of Trade limits the 
strain to 5 tons, or 11,200 lbs. per square inch. 
“ It must be abundantly evident, from the facts which have been produced, 
that the breaking strain, when taken alone, gives a false impression of, 
instead of indicating, the real quality of the iron, as the experiments which 
