THE ROYAL ARTILLERY INSTITUTION. 
201 
cast-iron shot of this weight, carrying a striking velocity of about 1300 ft. 
per second, is proof against their penetration at 800 yds. range. 
An experiment was made at Shoeburyness in May 1861, in order to 
ascertain what protection could be obtained against cast-iron shot, from 
brickwork, faced with iron plates of various thicknesses, from 2" to 2>\"* 
The general results obtained were as follows :— 
“ That masonry covered with 2 inch iron plates will effectually resist a 
12-pr. Armstrong shot at 600 yds. range. 
“ Covered with Z\ rr plates, it will effectually resist a 25-pr. Armstrong 
shot, at 600 yds. range. 
“ Covered with 3" plates, it will effectually resist a 40-pr. Armstrong shot, 
at 600 yds. 
“But the 3plates are not sufficient to resist the heavier natures of 
projectiles.” 
Granite faced with 4" iron plates is seriously injured by 68-pr. cast-iron 
shot, fired with the service charge, at 100 yds. range. In an experiment at 
Shoeburyness it was found that blocks of granite 3 ft. thick, faced with 
an iron plate 4" thick, were cracked through and split by the impact of a 
single shot fired under these conditions. The plates were of excellent 
quality and were only slightly indented. 
Big. If shows the form of cone which is invariably obtained 
from the impact of spherical or round-ended cylindrical cast- 
iron shot on iron plates. 
Fig. 1. 
The cast-iron shot of the service are generally made of soft grey foundry 
iron, which “ from the ease with which it breaks up, is of very little com¬ 
parative efficiency; and experiments have therefore been made with shot 
of an improved quality of iron, viz. Dr Price's improved pig iron, and some 
mixtures made in the Royal Laboratory. 
Mr Pairbairn made some experiments on Dr Price's iron, with a view of 
ascertaining its tensile strength; and in summing up the results of these 
experiments he states,— 
“ The average tensile strength of cast-iron has been found to be about seven tons 
per square inch,” 
whilst the mean of specimens cut from Dr Price's shot was 13*697 tons per 
square inch, or “ nearly double the strength of ordinary cast-iron.” 
* A detailed account of this experiment will be found in “ Proceedings,” R.A. Institution, Yol, 
III. p. 37. Remarks on Iron Defences, by Captain H. C. S. Dyer, R.A. 
f This and all the other drawings are taken from photographs made after the experiments at 
Shoeburyness. 
% Report, Special Co mm ittee on Iron, 1864. 
[VOL. IV.] 
26 
