426 Progress in Science, [July, 



of ammoniacal gas being 880, the whole heat expended during the trip would 

 have been sufficient to raise 84 gallons of water from the temperature of 

 83 Fahrenheit to the boiling-point, 212 . If for supplying this heat it was 

 necessary to rely upon the heat absorbed from the atmosphere, even on the 

 hottest day of summer, it is certain that a car loaded with passengers could 

 not run more than three hundred yards without being obliged to stop, and wait 

 at least fifteen or twenty minutes, in order to acquire sufficient heat from the 

 atmosphere to again run an equal distance. But the mechanical equivalent of 

 heat expended in working the engine by ammoniacal gas, one-seventh of the 

 total heat, according to the best physicist, is fully made up by the extra heat 

 of chemical combination becoming also sensible at the instant of the re- 

 absorption of the gas in the water surrounding the tubes. The register of the 

 pressure-gauge at the moment of starting, and during the trip, shows conclu- 

 sively that the extra heat compensates all losses. The mean pressure during 

 a trip remains essentially the same, if we take .into account the time necessary 

 for the transmission or equalisation of heat between the reservoir containing 

 the liquid gas and the re-absorbing water in which it is immersed. On the 

 last trip made with a street car, the gauge registered at the start 150 pounds ; 

 lost in pressure, in making i£ miles, 30 pounds; 'gauge then registering- 

 120 pounds. Upon stopping for ten minutes it registered 180 pounds, thus 

 gaining 60 pounds. On stopping at the end of the trip of seven miles, the 

 gauge remained stationary at 176 pounds. The above variations can easily be 

 explained. It is impossible to construct an apparatus in which the transmission 

 of heat would be instantaneous ; therefore,' in rapid travelling, the reservoir of 

 liquid ammonia becomes cooler than the water of re-absorption outside ; but 

 the difference never exceeds a certain point either way, the extreme of which, 

 in the last trip, starting with 150 pounds, was a difference of 45 pounds. The 

 maximum of pressure during one of the warmest days of summer was then 

 195 pounds. When the reflection is made that this tension was exerted in a 

 boiler, which stood 600 pounds hydraulic pressure, no other commentary is 

 necessary as to its entire freedom from danger ; and this is easily explained, 

 for as the temperature between the reservoir of liquefied ammonia and the 

 water of re-absorption diverges, the transmission of heat becomes more or less 

 rapid, in the direct ratio of their degree of divergence, — on this principle, that 

 the production of heat in the re-absorbing water is equal to its reduction by 

 evaporation in the reservoir of liquefied gas. One other advantage which 

 ammonia possesses over steam is the fact that its vapour, not being condensed 

 at the usual temperature of our atmosphere, does not, like steam, at a low 

 temperature, suffer condensation, either in the cylinder of the engine or when 

 used at a distance from the boiler. The cheapness of ammonia as a motive 

 power, when compared with steam, is owing to the fact that one steam-engine, 

 if it could be made to propel one hundred street cars with ease, would be much 

 cheaper than one 'hundred steam-engines, each requiring a separate fire and 

 an engineer, besides the regular conductor of the car ; but the case is far 

 different with ammonia, as a single engineer at the station can superintend the 

 supplying of two hundred cars with liquefied ammonia, in sufficient quantity 

 to run any distance within the limits of" a large city, by means of a single fire 

 under the stationary boiler in which the ammoniacal gas is liquefied. Further, 

 liquefied ammonia can be compared to a bottled-up power, which can remain 

 in a reservoir for months, or even years, and be transported anywhere in any 

 • desirable quantity ; and then at once, without any further preparation, can be 

 used for any purpose desired, and by the simple turning of a tap can be made 

 to act as powerfully as when first liquefied. The other advantages of ammonia 

 as a motive power are: First, its perfect safety — for the reason that its power 

 is exerted at a very low temperature, and consequently its influence in 

 weakening the tenacity of the iron vessel containing it is trifling, when com- 

 pared with the destructive effects of a high temperature : for it is a fact, known 

 beyond dispute, that the main agency which causes those frequent and 

 deplorable explosions of steam-boilers is the high heat they require for the 

 production of an effe'ctive force. Second, for marine purposes there is no 

 doubt that it will conquer for itself a high place before long, for this reason — 



