582 THE POPULAR SCIENCE MONTHLY. 



feet, we have $20,000 a year as the expenditure under this head, which 

 is probably well within the actual figures of most American works. 

 In the case of the electric plant four per cent is a sufficient allowance 

 for the same item, which gives a yearly charge of $12,000, and a cost 

 of six cents per 1,000 feet. 



Depreciation of this part of the plant varies but little with different 

 works, as the conditions upon which it depends are relatively constant, 

 but that of the mains is, on the other hand, exceedingly variable. In 

 a dry, open soil, gas-mains will last a great length of time, and even 

 when they become entirely rusted through they will still continue ef- 

 ficient if undisturbed. They do not, however, remain undisturbed, so 

 that in the most favorable conditions some expenditure is necessary to 

 keep them in working condition. We shall probably not be far wrong 

 if we take this at two per cent of the entire cost of the mains, which in- 

 cludes, of course, that of laying them. This item then becomes in the 

 case of our gas plant $5,000 per year, and 2-J cents per 1,000 feet. In 

 the case of the electric mains, this percentage must be reckoned only 

 upon their cost, exclusive of the copper, as this latter is practically in- 

 destructible, and can be used again and again. The amount upon 

 which to reckon the two per cent depreciation is therefore $2,200x50 

 =$110,000, and the yearly charge $2,200, which gives 1*1 cent per 

 1,000 feet. The interest on the investment is the same in each case, 

 and amounts to $24,000 a year, at four per cent, and to 12 cents per 1,000 

 feet. These items include all that are properly chargeable to the expense 

 account of the plant save taxes, which would be about the same in each 

 case, and which maybe neglected for the present. The plant account, 

 then, stands, in the two cases, for each thousand feet or its equivalent : 



Gas. Electricity. 



Interest 12" 12' 



Depreciation of producing works 10' 6* 



" of mains 2-5 1*1 



Total 24-5 191 



19-1 



Balance in favor of electricity 5*4 



The items entering into the cost of coal-gas are, exclusive of man- 

 agement, rent and taxes, etc., the cost of coal, of manufacturing, and 

 of distribution. Taking the last first, we find 4*4 cents per 1,000 feet 

 as the cost' of this item for the four metropolitan companies. Putting 

 this at 5 cents for American works, and deducting from this 2J cents 

 for the depreciation of mains, which is included in this charge, there 

 is left 2% cents for the cost of the labor of inspection of meters, etc., 

 which constitutes the charge of distribution, and which would be about 

 the same in both systems. 



As the depreciation of the mains is not given separately, this item 

 is liable to error, due to a wrong estimate of such depreciation, but, as 

 it affects both systems similarly, it will not vitiate the results. Under 



