FIRING WITH VARIOUS FUELS 37 



the peep hole should appear white hot, and should be con- 

 tinuous and not be stopped or checked each time the straw 

 is pushed in, as will be the case if firing be too heavy or too 

 much be put in at a time. Sometimes straw, especially 

 when damp, is pulled over against the ends of the tubes. 

 This may be scraped off with the poker, through the peep- 

 hole. The tubes should be cleaned twice a day. 



The draft should be strong enough to make the fire 

 burn freely and at a white heat. It may be necessary to 

 reduce the exhaust nozzle to get the proper draft, but it 

 should never be reduced more than is necessary, as back 

 pressure reduces the power of the engine. If unburnt 

 straw be seen coming out of the smoke-stack, it shows that 

 the exhaust nozzle is too small. Do not expect the engine 

 to steam well when the front end of the boiler is low. The 

 engine should be level or a little high in front. If the en- 

 gine -has been steamed up for some time without running, 

 the screen in the smoke-stack may be so filled up as to seri- 

 ously interfere with the draft. 



Brick Arch. For successful straw burning, it is im- 

 portant that the brick arch be tight so that no air can pass 

 through it, especially in front near the tube-sheet. It is 

 best to close all the joints and crevices with fire-clay, if it 

 is to be had, or if not, common clay may be used and it is a 

 very good substitute, especially if it be mixed with salt 

 water. Even common earth lasts very well if mixed with 

 salt water. 



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