584 THE POPULAR SCIENCE MONTHLY. 



more than one half the cost of the coal, while with most works it is 

 probably inconsiderable. The average price of the coal used may be 

 placed at $4.50 a ton, and the amount of gas produced 10,000 feet, 

 making the cost 45 cents per 1,000 feet. This make of gas can hardly 

 be maintained with a production of residuals equal to one half the cost 

 of the coal, but. assuming that it is, the cost of the coal becomes 22 

 cents per 1,000 feet. 



In the foregoing estimate of the electric plant, it has been as- 

 sumed that eight lamps could be maintained throughout the entire dis- 

 tributive system for each actual horse-power expended upon the pulley 

 of the dynamo-machine. That this is entirely feasible has been proved 

 by careful tests made by experts in no way interested in any of the 

 lamps, and their results can therefore be accepted without question. 

 For such a use as electric lighting, the cost of a horse-power may 

 safely be taken as not above the best results hitherto obtained in prac- 

 tice. In general manufacturing, the item of power, while important, is 

 not sufficiently so to demand that constant and great care necessary to 

 obtain the very best results, and hence few engines and boilers yield 

 in practice the same results as in special tests. With electric-light 

 companies, this item, on the contrary, is vital, and we may confidently 

 expect to see them in time obtaining their power at a considerably less 

 cost than is now common. Mr. Edison finds as a matter of fact con- 

 firmed by several months' test at Menlo Park, that he is able to maintain 

 a horse-power an hour with five pounds of slack (one third pea and two 

 thirds dust), costing $2.45 a ton. For the purpose of the present com- 

 parison, however, it is best to make a liberal allowance, and take for a 

 200-horse-power engine a consumption of four pounds of coal an hour, 

 the coal costing $4.50 per ton of 2,240 pounds, delivered. A horse- 

 power will then cost ^of a cent an hour, and we may rightly abate 

 our liberality sufficiently to include in this the cost of the oil for lubri- 

 cating the engine and dynamo. 



The maintenance for an hour of 200 electric burners, the equivalent 

 of the 1,000 feet of gas, will therefore cost 20 cents, as against 22-J 

 cents for the gas. 



Summing up the results so far obtained, the two accounts stand as 



follows : 



Plant Account. P ee ^O 00 Feet. 



Gas. Electricity. 



Interest 12' 12* 



Depreciation of producing works 10* 6* 



Depreciation of mains 2*5 1*1 



24-5 19-1 



Manufacturing expenses : 



Labor 12* 9* 



Coal 22-5 20- 



34-5 29- 



Working expenses : 



Distribution 25 2*5 



Total 61-5 60-6 



