The Effects of Impure Water. 439 
CaO, SO3 \CaO — CaO, CO^ 
{i. e. sulphate of lime)/S 0^ ^ ^-^^ i- e- carb. of lime 
(ck'posit) 
+ 
NaO, SO;, 
0.e.caib. otsuda) iCO,^ (in solution) 
" In Clarke's process, by which a good deal of lime is removed from certain 
hard waters by means of lime-water, i. e. a solution of caustic lime, the lime 
is only separated from the bicarbonate, and not from the sulphate of lime 
(gypsum). 
" In like manner, by sal ammoniac or chloride of ammonium we can only 
remove tiie lime from the bicarbonate of lime, but not from the gypsum, and 
hence caustic soda is superior both to lime-water (Clarke's process) and to the 
sal ammoniac process. The beneficial action of the caustic soda when added 
to hard water does not consist in the i)rcvention of insoluble lime-combina- 
tions, but in the almost instantaneous precipitation of these compounds in a 
Jinclij divided puluerulent condition. Sal annnoniac prevents the deposition of 
carbonate of lime, inasmuch as it forms with the carbonic acid of the car- 
bonate of lime volatile carbonate of annnonia, which passes oft' with the 
steam, whilst the chlorine in the sal ammoniac forms with the lime chloride 
of calcium, a very soluble salt which remains dissolved in the boiler. But, as 
stated already, sal ammoniac has no eft'oct on sulphate of lime. Altogether, 
caustic soda is not only the most efticacious, but also the cheapest means 
for preventing boiler incrustations." 
^ Some facts connected with this subject seem worthy of record in 
this Journal. For instance, in a steam boiler at Ems there was no 
trace of incrustation after several months' wear, although the water 
with which the boiler was fed contained not less than 21 '899 grs. 
in the poimd of solid matter. On analysis, the following results 
were ascertained : — 
Grs. 
Carbonate of soda 11"35488 
Sulphate of soda 0-10790 
Chloride of sodium T'l-'Tn'JO 
Sulphate of potash 0-43653 
Carbonate of lime l-24o70 
Carbonate of baryta 1-06890 
Carbonate of iron .. ■ 0*01728 
Carbonate of manganese 0'00868 
Carbonate of baryta and strontia 0'00215 
Phosphate of alumina 0-01090 
Silica 0-37839 
21-89951 
Fresenius inferred from this that it is not carbonate of lime, 
but only the sulphate of lime which causes the formation of crust, and 
he attributed the absence of incrustation in the instance under 
review to the action of the soda contained in the water. Starting 
from this point, he instituted an elaborate series of experiments, 
and from these he ultimately arrived at the conclusion that the 
addition of soda is the simplest means of preventing incrustation 
(vide Journ. ftir Prakt. Chem., Iviii. p. Go, quoted in the Pharma- 
