September 15, 1893.] 



SCIENCE. 



147 



We can divide the useful calories into three classes, 

 which we will call the c, r, and p calories, the c calories be- 

 ing those actually used in cooking, the r calories being 

 those used in raising the water in which the substance is 

 cooked to a cooking temperature, and the p calories being 

 those calories used in cleaning the cooking utensils, etc. 

 In the case taken, the c calories amounted to approx- 

 imately 30,000*. 



The cooking efficiency, or the ratio of the calories used 

 in cooking to the total watts in the coal, is therefore only 

 .03 (three one-hundredths of one per cent). 



The r calories amounted to 435,000. Adding them to the 

 c calories, we get the total cooking efficiency to be .46 

 (46 one-hundredths of one per cent). 



The p calories amounted to 2,256,000 approximately. 

 Adding them to the c and r calories, we get the total all 

 day ratio of the useful watts to the total calories in the 

 coal to be 2.7 per cent. 



The addition of the calories used in heating a hot-water 

 apparatus for baths, etc., adds about 1.5 per cent to the 

 efficiency, making the total all day efficiency of the stove 

 above 4. 2 per cent. 



The writer has been informed that Professor Tyndall, in 

 a test of the efficiency of a stove, obtained the figure of 

 six per cent. This, however, must have been the max- 

 imum' efficiency, as, without the hot-water coils (which 

 were probably not in the stove tested by Professor Tyn- 

 dall) the all day efficiency can hardly reach three per cent. 



There remain, out of the original 100,000,000 calories 

 in the coal, about 96,000,000 to be accounted for. These 

 evidently are lost up the chimney or are radiated out 

 into the room. We may make a rough calculation of 

 their relative and absolute amounts. 



The total radiating surface is, as given above, 37,200 

 square centimetres. Taking the average difference of 

 temperature between the stove and the room as eighty 

 degress C, and taking the coefficient of emissivity of the 

 blackened surface of the stove as .0004, we find for the 

 total loss in radiation, for the day of ten hours, 64,800,000 

 calories. The remaining 30,000,000 calories must go up 

 the chimney, or be left in the unconsumed coal. 



We may tabulate the results thus: 



1. Total amount of heat in coal, - 100,000,000 k. 



2. Amount used in actual cooking, - 30,000 k. 



3. Amount two plus amount used in raising 



water in which food is cooked to cook- 

 ing temperature, - _ _ 465,000 k. 



4. Amount used in cleansing cooking uten- 



sils, etc. (2,256,000) plus amounts 



2 and 3, - - - - 2,750,000 k. 



5. Amount used in heating bath, approxi- 



mately, - - - . 1,500,000 k. 



6. Amount used in warming room, - 64,800,000 k. 



7. Amount lost up chimney, and through 



incomplete combustion, - 31,000,000 k. 



Prom these figures we see that the name cooking stove 

 is really a misnomer, for of the total amount of useful 

 work which is got out of the stove, i. e., 69,000,000 cal- 

 ories, only 30,000, or about .04 per cent are utilized in 

 cooking, the rest being spent in warming the room, and 

 in heating water. It will be noticed that cooking stoves 

 seem to be designed to j)resent as much surface for radi- 

 ation as possible, and that the efficiency of the stove as a 

 water heater is only four per cent, while, with proper design, 

 a water heater should have at least fifty to sixty per cent 

 efficiency. 



The efficiency of the electric heater is very simply cal- 

 culated. 



*The c calories were obtained by weighing the food before and after, and 

 taking the loss in weight as due to evaporated water. This, of course, is not 

 strictly accurate, but it must be a fairly close approximation. 



A box, whose interior volume is eight cubic feet will 

 cook the same amount as the stove experimented upon. 

 The surface radiating heat will be, in this case, about 

 24,000 square centimetres, and, taking the emissivity at 

 .00025, we get for the total loss, since the current will be 

 only used six hours, as against the ten of the stove (as no ap- 

 preciable time is required to warm the electrical oven, and 

 the current may be cut off when not in use) a total of 

 7,000,000 calories lost by radiation per day, when there 

 is not a heat-retaining covering, such as asbestos, and the 

 bare tin is exposed to the air. It would be only 

 55,000,000 in actual practice, as one side would rest on a 

 table. 



By the use of proper insulation, the loss can be reduced 

 to one-tenth of this, or 700,000 calories. We thus obtain 

 the following table. 



1. Amount used in actual cooking, - - 30,000 k. 



2. Amount lost in radiation, - - - 700,000 k. 



Total cost at 1 cent per 100,000 calor- 

 ies (which is the actual selling price of 

 the electric companies at present, or 

 slightly above it, in some cities) 7.3 cents. 



If we include the amount of heat used in heating the 

 food up to cooking temperature, we get, 



1. Amount used in actual cooking plus amount 



used in heating up to cooking tempera- 

 ture, - - - . 465,000 k. 



2. Amount lost in radiation, - - 700,000 k. 



Cost at 1 cent per 100,000 calories, - 11.65 cents. 



If we include the amount of heat used in heating 

 water for cleaning kitchen utensils, water for bath, etc., 

 we get the following: 



1. Amount used for cooking plus amount used 



for heating to cooking temperature plus 

 amount used for heating water for clean- 

 ing kitchen utensils, water for bath, etc., 4,250,000 k. 



2. Amount lost in radiation, - - 700,000 k. 



Cost at 1 cent per 100,000 calories, - 42.5 cents. 

 The cost of the thirty pounds of coal, at 



$6.00 per ton, is - - - 8 cents. 



We see, therefore, from these figures, that, so far as 

 actual cooking is concerned, electrical cooking is about 

 ten per cent cheaper than cooking with an ordinary 

 stove. 



When we use the electric stove to heat the water- in 

 which the food is cooked to boiling point, we see that 

 electric cooking is thirty-five per cent more expensive, if 

 we take the ordinary prices ruling at present. As, how- 

 ever, a load due to cooking comes at a time of the day 

 when a load is much desired by station managers, and 

 would give a return at a time when the dynamos are 

 practically doing nothing else, it is certain that there 

 would be a deduction from the ordinary lighting rates, 

 and the electric oven would compare favorably with the 

 cooking stove under those conditions. 



When, however, we come to use electricity as a means 

 of heating water, for any purpose, we see that the electric 

 cannot hope to compete with the ordinary method, un- 

 economical as the latter is. We are led, therefore, to the 

 following, as the most economical method. 



A boiler for heating water can readily be designed that 

 shall have an efficiency of fifty per cent. This should be 

 used for heating water, and also for heating the house, by 

 means of the ordinary method of tubes. Means of effect- 

 ing this combination will readily suggest themselves. 



The electric oven should be used for cooking. 



With this system we get the following table: 



