THE ROYAL ARTILLERY INSTITUTION. 
261 
yet in this instance some comparatively weak point in the plate in 
question, though it had successfully resisted the force exerted by the 
very highly compressed air for a short period, was - eventually tried 
beyond the limits of its strength by the continued strain exerted by the 
air confined at a lower pressure; the powers of cohesion of its particles 
were suddenly overcome, when the confined air, released at one point, 
expanded with irresistible rapidity, tearing asunder the splendid metal 
which composed the air-chamber, and consequently inflicting fearful 
injuries on the poor fellows who were preparing to launch the torpedo 
on its trial trip. Most careful steps have been taken to avoid the 
recurrence of an accident of this nature, the possibility of which, with 
the precautions already adopted, was quite unforeseen. 
Other explosions of this class, which are of more than weekly occur¬ 
rence, and but too frequently result not merely in destruction of 
property but in more or less serious loss of life, are due to the bursting 
of boilers at factories, mines, and collieries, to say nothing of those 
which occur in buildings, in connection with heating appliances and 
with kitchen ranges, and bath- or other heating arrangements. The 
explosion of a boiler may arise either from an exceptionally rapid 
development of steam, the pressure speedily exceeding that which the 
boiler, or some portion of it, can withstand; or from an absence, or 
failure in the proper operation, of appliances for relieving the pressure 
in a boiler, by permitting the escape of steam, and giving warning 
when the pressure begins to exceed the limit of safety. The suddenly 
tumultuous evolution of steam may either occur from the boiler be¬ 
coming overheated in parts, in consequence of the shortness of water, 
or from the sudden cracking or peeling of a non-conducting incrusta¬ 
tion, or fur, on some part of the boiler, whereupon the water comes 
into contact with the overheated metal beneath it. But by far the 
chief causes of boiler explosions are defects in their construction or 
repair, and the reduction in thickness of the metal in parts by corrosion 
or oxidation, internally and externally, from long use and neglect of 
proper measures for periodically cleaning the boilers. 
The accidents due directly to the deposits formed from water in 
boilers have been very greatly diminished of late years by the applica¬ 
tion of preparations called boiler-compositions—of which there are 
many varieties, their general action being to prevent, more or less 
effectually, the carbonate and sulphate of calcium and other impurities 
in water which are separated by its ebullition and evaporation from 
producing hard impenetrable crusts or coatings upon the inner surfaces 
of the boiler. The judicious employment of a good anti-fouling pre¬ 
paration, and the thorough periodical cleansing of the interior of boilers, 
go far to guard against that source of danger; though, in adopting 
measures to diminish the formation of incrustations, care must also be 
taken to avoid promoting internal corrosion of the boiler by the agents 
used. 
The operations of the Manchester Steam Users* Association for the 
Prevention of Steam-boiler Explosions—founded, mainly through the 
instrumentality of Sir William Fairbairn, twenty years ago, and of 
which Sir Joseph Whitworth has also been a warm supporter from 
