SCIENCE OF THRESHING. I 17 



the boiler should be cleaned frequently and all 

 deposits removed. 



When boilers are worked to their fullest capacity, 

 and the engine makes a sudden demand for more 

 steam, the reducing of the pressure will suddenly 

 liberate a large quantity of steam, and the violent 

 effort this makes to escape from the surface of the 

 water, will cause increased foaming and priming. In 

 case the increased roaring in the exhaust gives 

 warning of this, the throttle may be closed momen- 

 tarily, and then opened again gradually, without 

 allowing the engine to lose much headway. 



