336 MARKET DAIRVING 
Tan bark is very cfficient 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 zine 
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. 
