354 



SCIENCE. 



[N. S. Vol. IV. No. 



was made by setting the engine in operation 

 and continuing its action until it had become 

 ' steady ' in all its essential conditions of oper- 

 ation, then by means of the steam-engine indi- 

 cator ascertaining the state, the quantity and 

 quality of the steam en route through the cylin- 

 ders, and measuring the power developed en 

 gros and net by the indicator and the Prony 

 brake and by their comparison. A suflBciently 

 complete description of the ejigine and the de- 

 tails of the accessory apparatus is given in the 

 paper of which this is an abstract. 



A delicate and accurate brake system per- 

 mits the measurement, with great precision, of 

 the quantity of work delivered to the strap of 

 the brake and its comparison with the exact 

 quantity of heat into which it is transmuted and 

 which is carried away by the water employed 

 for cooling it, the weight and change of temper- 

 ature of which are measurable with similarly 

 satisfactory accuracy. The outcome of the in- 

 vestigation, of which the detailed computations 

 need not be stated here, gave the value of the 

 heat-equivalent as 427.2 kgm. per calorie, as 

 the mean of six experiments, or within one-tenth 

 of one per cent, of that now accepted gen- 

 erally as the result of Rowland's determination 

 under similar conditions of temperature, 426.9. 



The figure 426.9, 778 foot-pounds in British 

 measures, has already come to be generally ac- 

 cepted by engineers in their computations rela- 

 tive to the heat-motors and this first exact com- 

 parison of the two energies on a large scale, and 

 especially using the steam-engine itself as the 

 apparatus of determination will undoubtedly 

 settle the question of the accuracy of that fig- 

 ure — certainly within the limits of precision 

 demanded by the engineer. 



The steam-engine has not usually been re- 

 garded as an instrument of precision; but the 

 six trials here recorded gave the figures, the in- 

 tegral numbers being taken, 428, 427, 422, 438, 

 428, 421, a degree of regularity being thus at- 

 tained which may appear surprising to one not 

 an expert in this field of applied science. For 

 all steam-engine trials it may be assumed that 

 henceforth the figure adopted for the Carnot 

 heat-thermodynamic equivalent will be taken 

 as 778 foot-pounds per B. T. U., 427 kgm. per 

 calorie. 



The investigation of the effect of drainage of 

 the steam-chest during the operation of the en- 

 gine, with the object of securing perfectly dry 

 steam at entrance into the steam-cylinders, 

 was made in a series of eight engine trials, 

 and at the constant boiler pressure and engine 

 power, as secured at the brake. When the 

 drain cocks were closed, the steam entered the 

 cylinders carrying 5 to 8 per cent moisture; 

 when open, the moisture ranged from 1.54 to 

 to 1.86 per cent. An effective separator at the 

 engine would have undoubtedly had a similar 

 effect, and the trials reported may be taken as 

 measuring the value of that now almost invari- 

 able accessory of the high-speed engine in this 

 country. The engine delivered about fifteen 

 horse-power during the trials. 



The results of these experiments showed that 

 gain by draining the moisture from the steam 

 before entrance, under the stated conditions, 

 into the cylinders, amounted to the following 

 quantities : 



Steam saturated at entrance. — The gain, un- 

 jacketed, was 9.29 per cent.; jacketed, 12.08 

 per cent. 



Steam superheated, — A loss was experienced 

 by drainage, of 5.33 per cent., unjacketed; 

 1.34 per cent., jacketed. 



Engine jacketed, economies. — With saturated 

 steam, the economy obtained by jacket action, 

 without drainage, was 26.47 per cent.; with 

 drainage, 28.73 per cent. 



With steam superheated, without drainage, 

 the gain was 25.02 per cent.; with drainage, 

 27.86 per cent. 



Steam superheated. — With steam superheated 

 4° C, the gain obtained amounted to 21.7 per 

 cent., without jacketing and without drain- 

 age, 9.07 per cent, with drainage; with jacket- 

 ing it amounted to 20.16 per cent, without 

 drainage, 9.07 with drainage. With jackets 

 in operation and without drainage, the gain by 

 superheating was 20.16 per cent., and with 

 drainage 7.7 per cent. 



It thus appears that separation of the mois- 

 ture from the entering steam is found to be an 

 important matter ; with superheated steam any 

 drainage is obviously, as here shown by direct 

 experiment, wasteful. 



