Agricultural Steam-boilers. 
431 
a. vcvy slight degrcp, the water would have immediately passed into the con- 
dition of Steam, which, hy its very great elasticity at high temperatures, would 
have blown the vessel to pieces. On the other hand, when the pressure of the 
air has been entirely removed, water boils at a temperature not above that which 
it naturally has ou a hot day." 
As boilers having an incrustation on tlioir inner siurface, in conse- 
quenco of a deposit of the impmities in water, are liable to " bum," it 
is highly important to prevent such incrustations, and thereby dimi- 
nish the chances of accident. A discovery with this object in view — 
it cannot be termed an invention — has been made by Mr. Spiller, the 
manager of the Chemical Establishment in the War Department, and 
has been for some time in use in the Government works at Woohvich. 
The mode of proceeding is thus described : — 
" Chemical Estahlishuwnt of the War Department, 
Woolwich, March 22, 1862. 
" Memorandum respecting the Prevention of Incntstation in Sfeam-hoilers. — 
The hard mineral deposits which gradually accumulate on the interior surfaces 
of steam-boilers owe their forination to the presence of lime and other impurities 
in the feed-water. By the gradual heating and evaporation of the water these 
calcareous matters are slowly deposited in a semi-crystalline form, and give 
rise to adherent crusts, often of considerable thickness and strength, which 
render it necessary to interrupt the action of the boiler at short intervals in. 
order that it may be opened and cleansed by chipping or some such laborious 
mechanical means. If, however, a small proportion of crude caustic soda be 
mixed with the contents of the boiler at first starting, and occasionally renewed 
durins: the continuance of its working, this chemical agent will be found to 
have the property of immediately precipitating, in a granular or sandy form, 
the greater portion of the lime compounds originally dissolved in the water. 
These small particles readily subside as a kind of mud, and may be ejected 
from the boiler by opening the lower ' blow-off' cocks for a few seconds once 
or twice during the day. 
" The dose of caustic soda necessary to be employed for this purpose will 
vary according to the degree of hardness or the amount of lime in the water : 
as a general rule, three or four pounds per week will serve for a boiler of 
20-horse power. In all cases it will be advisable to keep the proportion at a 
minimum, since the use of a large excess has undoubtedly an injurious tendency 
in disturbing the steadj^ and proper action of the boiler. By employing this 
small quantity of soda, the scale will become so diminished in amount and 
thickness as to permit of the boiler being used much longer than the ordinary 
period without inconvenience. There are several methods of introducing the 
soda. It should first be dissolved in water ; and it will usually be advantageous 
to prepare a solution of known strerigth — say 3 lbs. in a gallon — which can be 
measured from the stock as required, and either poured through the safety- 
valve or pumped in with the feed-water. 
" An inspection of the interior of the boiler after a preliminary trial will 
aiford the most satisfactory indication of the economy of the jirocess, and enable 
a judgment to be formed in regard to the proportion of material to be employed. 
It is difficult to avoid altogether the formation of a thin scale ; but, on opening 
the boiler, the deposit should be trifling in amount and of so soft a nature as 
to permit of its easy removal from the iron plates. There is not the slightest 
possibility of the soda exerting any corrosive action upon the metal of the "boiler 
or fittings ; its alkaline properties are known to have a tendency to preserve 
the iron from rust. 
