BOILER AND MANAGEMENT 169 



Tan bark is very efficient in removing boiler scale but 

 may injure the iron. 



Kerosene answers the same purpose but renders the 

 steam unfit for use in the dairy. 



When the water is salt or acid, a piece of metallic zinc 

 occasionally placed in the boiler will prevent corrosion. 

 Water of this kind can usually be told by its corrosive 

 effect on copper and brass. Acid water can also be de- 

 tected with blue litmus paper, which it turns red. 



WET AND DRY STEAM. 



Wet steam. This is steam holding in suspension ex- 

 tremely small particles of water which are thrown off 

 from the water surface while steam is generating. The 

 following are the causes of wet steam: 



1. Impure water in the boiler. 



2. Too much water in the boiler. 



3. Too little evaporating surface for the amount of 

 steam used. This is one of the chief objections to upright 

 and too small boilers. 



4. Violent agitation of the water in the boiler caused 

 by too rapid a generation of steam. 



Wet steam causes "priming" and is wasteful of heat. 



Dry Steam. This is saturated steam holding no water 

 mechanically in suspension. High steam pressure and a 

 large steam space above the water level are conducive 

 to dry steam. 



