$86 THE POPULAR SCIENCE MONTHLY. 



materially reduced if the resistance of these latter can be increased ; 

 while any improvements affecting the number of lamps per horse- 

 power diminishes both the interest account by reducing the plant and 

 the actual cost of production. 



How far coal-gas can go in a reduction of the cost of production it 

 is difficult to say, but I think the lower limit may safely be taken at 

 the point at which the sale of residuals pays for the coal. Both of 

 these items cost of coal and prices of residuals are practically be- 

 yond the control of a gas company. The coal is already purchased in 

 the open market at the lowest figures at which it can be obtained, and 

 the market for residuals depends chiefly upon the development of 

 chemical industries, which can hardly be hastened by the action of a 

 gas company. This market is a steadily growing one, and it is not 

 impossible that the residuals will in time pay for the coal, though it is 

 hardly probable. The items of labor and distribution can not probably 

 undergo any considerable reduction. The limit, then, below which it 

 does not appear that there is any probability of coal-gas falling in this 

 country is 46 cents per 1,000, which is a figure that may be reached 

 by electricity without assuming anything less, probable than the above 

 supposition respecting gas. It is only necessary to get ten lamps per 

 horse-power, and produce the latter with three pounds of coal an hour, 

 to bring the cost down to 47 cents, exclusive of the lamps. 



As a present competitor, however, what is known as water-gas 

 gas produced by the decomposition of steam in the presence of coal or 

 oil appears to be the more formidable. This mode of gas-manufact- 

 ure has the advantage of coal-gas in a lessened cost of the producing 

 plant, a smaller labor account, and a decreased depreciation of the 

 generating apparatus. Its successful competition with coal-gas ulti- 

 mately depends upon what the latter can make of its residuals, as there 

 is no offset of this kind in its case, but with present conditions it can 

 go below it. The producing portion of the plant costs but little more 

 than half that for coal-gas, while the labor is about a third, and depre- 

 ciation but slightly more than this. A sixteen-candle gas will require 

 three gallons of oil per 1,000 feet, and can be made with oil at 5 cents 

 a gallon and coal at 84.50 a ton, at an expenditure of 28 cents per 

 1,000 feet for materials. The total cost will not exceed 60 cents. 



Such, then, appears to be the relation of these two agents on the 

 basis of illumination solely, but it must not be forgotten that the 

 amount of light which each plant can furnish does not represent the 

 actual relative capacity of the two. The electric plant can be run 

 not only four hours a day for light, but any further number of hours 

 for power, without any increase of the machines. The gas-plant, on 

 the other hand, would have to be increased, to furnish both power and 

 light. That this advantage of electricity is liable to be a very impor- 

 tant one will hardly be questioned, when the extent of the field open 

 to electro-motors is borne in mind. 



