88 SCIENCE OF SUCCESSFUL THRESHING. 



to wash in the tank, as even a small quantity of soap is liable 

 to cause trouble. On account of the soap used in manufac- 

 ture, new boilers are liable to foam until they are washed 

 out two or three times. It is difficult to tell exactly how 

 much water there is in a foaming boiler, but it is probable 

 that some of it is being drawn over with the steam, and 

 therefore, the pump should feed more than the usual amount. 

 Do not run too long with a foaming boiler, but close the 

 throttle occasionally to see how full the boiler is when the 

 water settles. The remedy for foaming is to keep the boiler 

 clean and to use clean water. Foaming often causes priming. 

 Foaming and priming are more apt to occur with low than 

 with high steam pressure. 



Priming. When water is drawn over into the cylinder 

 with the steam, the engine is said to "prime." A priming 

 engine appears to be working very hard, exhausting heav- 

 ily, throwing water from the stack and often making a loud 

 knocking or pounding noise in the cylinder. Priming may 

 be caused by : i . Too much water in the boiler. 2. Too 

 low steam pressure. 3. Engine working hard with the front 

 of the boiler low. 4. Boiler working beyond its capacity. 

 5. Foaming. 6. Piston rings or valve leaking. 7. Valve 

 improperly set. 



In case the engine should begin to prime, the cylinder 

 cocks should be opened and the throttle partially closed, so 

 that the engine runs quite slowly, until dry steam comes 

 from the cylinder cocks. Priming is liable to knock out a 

 cylinder head, break the piston head, or do other serious 



