The Effects of Impure Water. 
435 
occurring cither at starting in the morning or after some period of 
cessation of work. 
in reply to rrofessor Wilson, it was stated by Mr. Amos that in his 
opinion no boiler is safe in the present day, unless it has a glass 
gauge and a gauge cock. The glass gauge is liable to accident, and 
therefore it is necessary to have two strings to the bow. Many 
boilers have sustained damage entirely owing to a shortness of 
water, which is, in fact, one of the chief causes of accident. 
The Effects of Impure Water. 
Mr. T. Beale Browx remarked that, owing to the hardness 
of the water in the Cotswold district, steam-boilers fed with it 
are peculiarly liable to incrustation ; but by adding a little lime- 
water to the hard water, the salts of lime are precipitated, and the 
water becomfes soft. Professor Wilson said the water of the Cotswold 
district has been found, on analysis, to contain a large portion of 
carbonate and sulphate of lime. Although the addition (jf lime to 
water containing the salts of lime in large quantities for the pur- 
pose of purifying it may at first appear pai^idoxical, it is founded on. 
strictly chemical principles. Pure lime is only sparingl}' soluble in 
water : if one dose or equivalent of carbonic acid be added, it is 
rendered far less soluble than before ; but on the addition of a 
second dose of the same acid, it becomes perfectly soluble. It is 
in this condition, as a bi-carbonate, that lime, generall}' speaking, 
exists in water, and more especially that of the Cotswold hills and 
all calcareous ranges of hills. By the addition of a small quantity 
of lime water to the supply water of the boiler the bi-cavLonate of 
lime contained in it is reduced to the condition of carLoiiatc, and 
being thus rendered comparatively insoluble will form a precipitate 
at the bottom of the tank instead of the boiler. The lime water is 
I'cadily made by mixing fresh burnt lime with cold water — say, in 
the proportions of a teacupfull of lime to a gallon of water. 
Mr. Amos said he had found that a change in the quality of the 
Avater with which an engine is supplied produces a good etfect — • 
the water used one day removing the incrustation produced by that 
used on a previous day. Peaty water produces in this way a bene- 
ficial effect, and so also does the tannin left in bark. 
Sir E. Kerrisox expressed similar opinions as to the benefits- 
resulting from a change of water. 
Professor Wilsox objected to the introduction of any vegetable^ 
substances into the boiler, as they can only act by decomposition, 
which (in the case of bran, potatoes, &c.) is very offensive when the 
valves are opened or the steam is blown off'. 
Mr. Frere suggested, as a practical remedy for the inconvenience 
of foul water, that farmers, wherever it Avas practicable, should 
have a good circular tank connected with their barns. If baiiis 
were properly slated, the tank would in ordinary seasons furnish 
sufficient water for the engine, and there would thus be an end of 
the evil and inconvenience arising from impurity. 
On the ef&cacy of caustic soda (or hvdrate of soda XaO, IIO) in 
2 F 2 
