WATER—ITS IMPURITIES.

15

for cleaning and inspection. These will tend very considerably to lessen theadhesion of calcareous crusts, and are in no way affeCted by the boiler fluids incommon use.

Soda crystals and caustic soda may be used with great success in boilers toeffect the immediate precipitation of the lime salts, and they aCt by throwingdown a finely divided form of carbonate of lime, which in turn furnishes nucleifor the deposition of subsequent accretions both of the carbonate and sulphate,so that they are prevented from crystallising upon the walls of the boiler. Agranular mud is thus formed, which subsides quickly, and may be for the mostpart got rid of through the “ blow off” cock, which should be opened for thispurpose two or three times every day, and run out with as little water aspossible.

The use of caustic soda has undergone a thorough trial in the boilersof the Royal Arsenal, Woolwich, and we are enabled to give the followinggeneral instructions regarding its use, which are based upon an experienceof upwards of ten years. The caustic soda should be dissolved in waterso as to make a concentrated solution of sp. gr. .1300. This being per-fectly miscible with water may be introduced into the boiler with thefeed-water at any time when, from the pressure of steam, it may notbe convenient to pass it through the safety-valve or other openings inthe boiler. But when the steam is down there is no difficulty in introducingthe prescribed dose by using a tin funnel with flattened aperture to pass itthrough the safety-valve, or a tubular arrangement with double cocks willanswer at all times. Half a gallon per diem is the average quantity foundsufficient for a 20-horse power stationary boiler working with Thames water forten hours in the day. If the water should happen to be unusually hard a largerdose may be employed, but it would not be expedient to add in one chargemore than the day’s consumption. Locomotive and multitubular boilers havebeen worked successfully with caustic soda, and it is here that the importanceof using anti-incrustation fluids makes itself most apparent.