Proceedings of the P oLYTEcnyic Association. 847 



terminated when the last coal is nearly burned. This plan is sup- 

 posed to give an accurate measure of the coal burned. The better 

 plan is, to get everything in average working condition before start- 

 ing to experiment. The steam should iiave the proper pressure ; the 

 fire be clean, and of a certain thickness, judging by marks on the 

 sides of the furnace ; the ash-pits clean, and the water at a certain 

 known height. The experiment may then proceed, weighing all the 

 coal afterward used, and measuring the water pumped into the 

 boiler, till near the desired time to stop, when the lire should be 

 tlioroughly cleaned and tilled up with coal to the same marks as at 

 the beginning, and should be maintained at that point, with the 

 steam at the starting pressure, till after pumping in the last tank of 

 water, when, as soon as the water level reaches the same height as at 

 starting, the experiment may be terminated, Tlie ashes in tlie pit 

 should then be weighed, as well as those previously collected. The 

 fire should be ecpially bright, and the steam pressure the same at the 

 beginning and end of the experiment, so tliat the water level will be 

 disturbed in like manner. At starting and stopping, a certain feed 

 should be kept on, or the water should be pumped too high, and time 

 noted when, by evaporation, the level falls to the mark. No experi- 

 ment should be less than eight hours in length, and a trial of forty- 

 eight to seventy-two hours' duration can better be depended upon. 

 During the experiment a log should be kept, upon which should be 

 recorded the time, the weight of the ashes, the number of tanks of 

 feed water, and the temperature of each. The temperature of the 

 escaping products of combustion and of the fire room may also be 

 noted, as well as any evident remarks about the kind of coal, and the 

 circimistances of tlie trial. After the experiment, the following cal- 

 culations are necessary: First, in an evident manner, ascertain the 

 total amount of coal and ashes ; subtract one from the otlier, which 

 gives the total weight of the combustible. Then find the average 

 temperature of the feed water and the average pressure of steam, and 

 calculate the weight of the whole quantity of water evaporated, 

 making allowance for its temperature. 



The next step is to find the quantity of water evaporated from a 

 constant temperature, say. 212 degrees. From formula or tables find 

 the total heat of the steam due to its mean total pressure; from this 

 deduct the total lieat which the water contained before entering the 

 boiler. The result is tlie numljer of units of heat imparted to each 

 pound of water. Divide this by the latent heat of steam at 212 



