944 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



engine of Count du Trembley Avould liave continned rnnning had there 

 not been immense difficulty and x^eril in nsing ether in recii)rocating en- 

 gines and i)mnps. 



It occurred to me to introduce a form of condenser and refrigerator 

 consisting of tubes within tubes, as described further on, which reduced 

 the Yohime of ether, distributed over a wide surface within a narrow 

 compass, and enabled me to construct an apparatus of great solidity and 

 safety. At the same time, one inconvenience attending the ether-ma- 

 chines was that the brine used, common salt and water, was aj^t to freeze 

 up in the refrigerator-tubes and burst them. This I overcame by the 

 use of an aqueous solution of glycerine, and later on I have economized 

 by using chlorine of magnesium and water, with some glycerine added, 

 according to the temperature at which it is jiroiiosed to work. 



Without attempting a detailed history of improvements suggested 

 from time to time, my main object for years was to overcome the then in- 

 evitable use of a reciprocating-pumx) in which liquefiable gases were alter- 

 nately liquefied and volatilized, to the detriment of efficiency. This was 

 found one of the most objectionable features in the use of sulphurous 

 acid and ammonia, inasmuch as a film of liquid remains after every 

 stroke between the piston and the cylinder-cover, and expands on the 

 return stroke so as to interfere with the suction of a fresh charge. 



I must enlarge somewhat on this subject of 



E. -ENGINES AND PUMPS. 



In all freezing-machines, except those dependmg on absorption of a 

 gas by water and its distillation, it has been a matter o± primary imj^or- 

 tance to secure an economical engine, and a pump capable of producing 

 a vacuum, or compressing a liquefiable gas. 



All kinds of engines have been used — upright and horizontal high- 

 pressure and compound engines. The inevitable waste, attending the 

 production of steam, and its imperfect utilization, in the best form of 

 reciprocating engines, have been regarded as really incurable evils, in 

 the production of artificial ice by means of pump-machines. 



The method of transmitthig power has necessarily attracted consider- 

 able attention, and in one machine the craulv-shalt; has been the seat of 

 all strain, whereas in other cases, with an engine placed on a bed-plate 

 on a line with the pump, the pressure on the engine-piston was greatest 

 when there was least resistance, and vice versa. 



But the difficulties of the engines, common to all machines using steam, 

 appeared of less importance than the imperfections of the reciprocating 

 pump. Whether single or double acting, the change in the direction of 

 motion at every stroke, the universal clearance or imperfect discharge 

 of the gas from the pump at each revolution ; the cumbersoDie and noisy 

 valves, which are frequently broken by striking ; the leaky stuffing-boxes, 

 and the ample surface of the piston-rod, for exposing a layer of gas to 

 atmospheric contact, as maaiy times per minute as the piston runs its 



