and Water used for General Purposes. 
161 
water ceases to give a brown colour, and yields a white-coloured 
precipitate with nitrate of silver. 
Clark's process has been tried on a large scale, and is in suc- 
cessful operation in many dye-works antl other manufactories, 
where large quantities of soft water are required. The water 
used by railway companies for feeding their engines is also 
softened in several places by this useful and extremely simple pro- 
cess ; and by it the Water Works Company, at Caterham, has for 
some vears past rendered hard chalk spring-water deliciously 
soft and pure before delivering it to the inhabitants of Caterham. 
The only drawback in working this process on an extensive scale 
is the difficulty of finding space for precipitating reservoirs, and 
storing for an additional 24 hours the immense volume of water 
which is required for the supply of large cities. However, this 
difficulty after all resolves itself into a question of expense, which 
is of no account in the case of private houses, in which Clark's 
process can be carried out very well without much difficulty. 
In conclusion, a few lines on the prevention of boiler incrus- 
tations may be considered serviceable. 
Ordinary boiler incrustations, resulting from the use of hard 
water, consist chiefly of carbonate and sulphate of lirne, as will 
be seen by the following analysis of a sample which I examined 
some time ago : — - 
Composition of a Boiler Incrustation. 
Dried at 212=. 
Grains. 
"Water of combination 4 • 59 
Oxide of iron 'SS 
Phosplioric acid "68 
Carbonate of lime 71 "06 
Sulphate of lime 12"75 
Lime in a state of silicate ., 1"58 
Magnesia in a state of silicate 3 "23 
Soluble silica 5 ' 70 
100-00 
Carbonate of lime separates gradually from hard water when 
the temperature is raised to the boiling-point, and in the course 
of time assumes a crystalline form. Hard crystalline masses 
or stone-like deposits are thus formed in steam-boilers, which 
greatly interfere with the economical production of steam. 
The best plan of preventing the formation of boiler-deposits 
like the sample, the analysis of which has been given, is to soften 
the water by Clark's lime-process. 
The next best plan, in my judgment, is to add to the water 
a solution of caustic soda ; to allow the precipitate to settle, agd 
to use the clear water for feeding the boiler. 
Or if it be considered too much trouble to soften the water in 
VOL. XI. — S. S. M 
