The Effects of Impure Water. 
437 
dissolving it at once in a known bulk of water, — say 3 lbs. or 4 lbs. in a 
gallon, and keeping this in an iron vessel ready for immediate use by measure. 
" For boiler purposes, always employ a small qiiantity in the first instance, 
and watch the effect ; very little is required to prevent the formation of incrus- 
tation, and a large excess is apt to induce a tendency to "priming." Caustic 
soda does not exert any corrosive action upon the iron boiler-plates and fittings, 
but inasmuch as it atlects the humau skin even more than strong washing 
soda, it should not be handled unnecessarily. 
" As to its mode of action : supposing it to be employed with an average 
sample of river or well water, containing both sulphate and carbonate of lime, 
it will be found to have the power of precipitating immediately and i7i a 
granular form those lime salts which otherwise would adhere by crystallization 
to the surfaces of the boiler. According to chemical theory, one equivalent of 
caustic soda suffices to precipitate two equivalents of carbonate of lime 
according to the following equation : — 
Sulphate of Bicarbonate of Carbonate of Sulphate of 
Caustic Soda. Lime. Lime. Lime. tioja. Water. 
NaO, HO + CaO, SO3 + CaO, 2 COj = 2 CaO, CO., + NaO, SO3 + HO. 
" It can thus be shown, that in point of economy no cheaper alkaline 
product is likely to be found than that proposed, commercial samples of which, 
are always priced exactly in accordance with the percentage of true soda 
which they contain. 
" In the discussion upon the use of chloride of ammonium for boiler jair- 
poses, it was not suggested that this substance acts injuriously in corroding 
the iron. With reference to the use of lime lor .softening water in the boiler 
a practical difficulty arises from the circumstance that the finely-divided 
particles of slaked lime are exceedingly liable to cause priming. 
" John Spiller, F.C.S." 
The following letter from Dr. Voelcker fullj' supports Mr. 
Spiller's view, and furnishes a more detailed explanation of the 
chemical changes which arise from the use of this and other 
remedies. 
" August 13th, 1862. 
" Boiler explosions, I have no doubt, are often produced when the fur 
which certain hard waters form on boiling is not removed. The far or 
incrustation found in boilers consists principally of carbonate and sulphate of 
lime. It likewi.se contains fluoride of calcium, some phosphate of lime and 
magnesia, and oxide of iron. When gradually deposited these constituents of 
hard waters assume a very hard crystalline condition, and form a regular pan 
or firlse bottom, on which the water in the boiler rests without coming into 
actual c ontact with the heated iron-boiler. The consequence is that the iron 
soon burns out, or, in chemical language, becomes oxidised into the black, 
scaly oxide of iron, which peels off, and gradually renders the boiler so weak 
that it must burst when the temperature is suddenly raised. I believe in this 
way boiler explo.sions are frequently produced. It is, therefore, the aim of 
intelligent men, and ought to be the aim of every one who is compelled to 
feed a steam-boiler by hard water, to prevent the deposition of sulphate and 
carbonate of lime, and other minej'al matters in the shape of a hard crystalline 
mass. This may be done in two ways : — 
" 1. The deposition in crystalline hard masses may be prevented by the intro- 
duction into the boiler of a mechanical disturber of crystallisation. Spent tan 
and sawdust are as good as anything that may be used. The insoluble salts 
