MECHANICS AND USEFUL ARTS. 41 



With a view of testing this point, and also for the satisfaction 

 of railway engineers, of conducting experiments at locomotixe 

 pressures, a thorough remodelling of the whole apparatus was 

 effected. The tappet motions were thrown aside in favor of the 

 usual slide-valve arrangement, working Avith a moderate amount 

 of expansive action. The former wasteful vertical boiler was 

 discarded in favor of a more economical one of the compound or 

 Cornish multi-tubular description, so as to obtain a better evapo- 

 rative duty from the coal consumed. The radiating surfaces of 

 the cylinder-pipes were reclothed, and the feed water heated by 

 the exhaust steam. Instead of exposing the air-pipe to the direct 

 heat of the furnace, as in the former case, the air became 

 thoroughly heated on its passage from the pump to the boiler at 

 a temperature of from 500" to 600° Fah., by being conducted 

 through suitable coils and pipes through the exhaust steam In the 

 heater, and the waste heat in the boiler flues and uptake. 



When these changes were made a gain of 47 per cent, over 

 steam only, was claimed on an even-pressure trial, and a gain of 

 nearly 30 per cent, on an open-valve trial, a step in advance so 

 huge that it staggers belief. 



AMMONIACAL GAS ENGINE. BY F. A. P. BARNARD, LL.D., COM- 

 MISSIONER TO THE LATE FRENCH EXPOSITION. 



If hot-air engines and inflammable gas engines fail as yet to 

 furnish power comparable to that which steam affords, without a 

 very disproportionate increase of bulk, and for high powers fail 

 to furnish it at all, the same objection will not hold in regard to 

 the new motors now beginning to make their appearance, in 

 which the motive power is derived from ammoniacal gas. The 

 gas, which is an incidental and abundant product in certain man- 

 ufactures, especially that of coal gas, and which makes its ap- 

 pearance in the destructive distillation of all animal substances, is 

 found in commerce chiefly in the form of the aqueous solution. It is 

 the most solul^lc in water of all known gases, being absorbed, at the 

 temperature of freezing, to the extent of more than 1000 vol- 

 umes of gas to one of water, and at the temperature of 50° F. 

 ot more than 800 to one. What is most remarkable in regard to 

 this property is, that, at low temperatures, the solution is sensibly 

 instantaneous. This may be strikingly illustrated by transferring 

 a bell-glass filled with the gas to a vessel containing water, and 

 managing the transfer so that the water may not come into con- 

 tact with the gas until after the mouth of the bell is fully sub- 

 merged. The water will enter the bell with a violent rush, pre- 

 cisely as into a vacuum, and if the gas be quite free from mixture 

 with any other gas insoluble in water, the bell will inevitably be 

 broken. The presence of a bubble of air may break the force of 

 the shock and save the bell. 



This gas cannot, of course, be collected over water. In the 

 experiment just described, the bell is filled by means of a pneu- 

 matic trougli containing mercury. It is transferred by passing 



