Cresson.] -^70 [July 17, 



The crown-sheet of the furnace of this locomotive, vsdth its stays and 

 girders, weighed 1,110 lbs., and had a surface of 22 square feet, this gives 

 a mass of iron equal to an average of 50.45 lbs. per square foot, or an 

 average thickness of 1.23 inches of iron plate. 



Such a plate could therefore raise a stratum of water 1.23 inches in 

 depth 1° Ft. fv^r every 1° Ft, of temperature lost by the iron, or would 

 convert a stratam of water 0.00123 inch in depth into steam. 



In our second example, we supposed the temperature of the iron to 

 have fallen from 660° Ft. to 485° Ft., a loss of 175° ; this would give us 

 0.00128 X 175 =0.21525 inch as the depth of water converted into steam, 

 and which, under the conditions stated, would give a pressure of nearly 

 87 atmospheres in addition to that already existing within the boiler by 

 the transfer of heat from the iron. 



This leads to the conclusion that the substitution of a crown-sheet j\ 

 inch thick, stayed without girders, would reqtiire the contraction of the 

 space between the crown-sheet and the roof of the boiler to an average of 

 2| inches, to allow of the sudden production of a pressure of steam equal 

 to that capable of development in a boiler constructed as was the one 

 exploded, or the effect of an equally overheated crown- sheet would be 

 reduced to ^ of that which would otherwise have been produced. 



That such is the fact was clearly shown by the result of a recent 

 accident to another locomotive in which the crown-sheet was simply 

 forced down, as by a gradual increment of pressure tearing out the 

 stay-bolt and j)ermitting the steam and water to escape into the fire- 

 box and extinguish the fire without further injury to the boiler or engine. 



C. — Level op Water in Boilers. (How Affected.) 



There are several conditions under which an engineer may be deceived 

 as to the level of the water in the boiler of a locomotive-engine. The 

 most important are : 



1. Priming or rise of water-level. 



2. Changes of grade. 



3. Variations in the speed of the engine. 



In all boilers the level of the water is somewhat raised whenever steam 

 is taken off. The amount of the rise is varied by the rapidity with which 

 steam is conveyed away : the form of the boiler and the manner in which 

 heat is applied for the production of steam. 



In boilers in which there are narrow water spaces surrounding the fire- 

 box, and those in which heat is conveyed to the water locality, that is, 

 the heating surfaces are small in extent as compared with tte whole vol- 

 ume of water, and are very hot, the lift of the water is very considerable 

 whenever an outlet for steam is opened, amounting in some instances to 

 as much as 12 and 14 inches. 



In ordinary locomotive boilers the rise upon opening the throttle or 

 safety-valve averages about 4 inches. 



The presence of oil in the boiler greatly increases the foaming. The 



