254 DAIRYING. 



P = boiler pressure; 



A = area of valve; 



V= weight of valve; 



zv = " " lever, 



JV = weight hung upon the lever. 



Firing. — Firing should be gradual, and the grate kept com- 

 pletely covered with coal or ashes. The fire should not be more 

 than four or five inches deep unless the pieces of coal are large, 

 in which case the depth may be increased. 



The fire-doors and flue-doors should not be opened in order to 

 keep down the steam pressure. This practice not only wastes 

 fuel but is injurious to the boiler, and will not be necessary if 

 the boiler is properly attended to. 



Priming or Foaming. — Foaming is a rapid disturbance of the 

 water, in consequence of which it rises in the boiler in the form 

 of spray or foam; it is usually caused by dirty water, presence 

 of oil, etc., the boiler not having been cleaned for some time or 

 not thoroughly cleaned. Foaming may, however, be due to 

 other causes, such as too small a steam space, sudden demand 

 of a great quantity of steam, etc. In case a boiler foams all 

 steam connections should be shut off and the fire dampened by 

 means of a fresh supply of live coal or ashes. These precau- 

 tions will usually suffice to allow the water to settle, and to 

 enable one to ascertain the true water level. If the glass shows 

 a small amount of water, start the pump, or injector, and fill the 

 boiler to a point between the second and third gauge. The 

 boiler may then be blown off to the first gauge by means of the 

 surface blow-off, if one be present, and if not present the regular 

 blow-off valve may be used. This operation being repeated, 

 the impurities are gradually diminished, but care must be taken 

 that the water level does not fall below the top of the flues. 

 The boiler can now be used as before, but in all cases it should 

 be thoroughly cleaned as soon as possible. 



Removal of Scale. — Potatoes, about eight or ten in number, 

 are sometimes placed in the boiler after cleaning. Soda or 

 kerosene may also be injected with the feed-water in quantity to 

 be determined by observation. Boiler compounds should be 

 used with caution, and when used should be obtained from a 

 reliable dealer. Too great a quantity of any of the above will 

 be harrnful. 



