SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



it was I. nt 0.262 indicated, with a brake horse-power of 0.144, or 55 per cent of 

 that indicated. 



With these results both of theoretical calculation and practical experiment, 

 all thought of propelling the proposed aerodrome by electricity was necessarily 



abandoned. 



Carbonic-Acid Gas 



At the first inception of the idea, it seemed that carbonic-acid gas would 

 be the motive power best adapted for short flights. It can be obtained in the 

 liquid form, is compact, i>ives off the gas at a uniform pressure dependent upon 



temperature, and can be used in the ordinary steam engine without any 

 essential modifications. The only provision that it seemed, in advance, neces- 

 sary to make, was that of some sort of a heater between the reservoir of liquid 

 and the engine, in order to prevent freezing, unless the liquid itself could be 

 heated previous to launching. 



The engines in which it was first intended to use carbonic acid were the little 

 oscillating cylinder engines belonging to Aerodrome No. 1. The capacity of 

 each cylinder was 21.2 cu. cm., so that 84.8 cu. cm. of gas would be required to 

 turn the propellers one revolution when admitted for the full stroke, and 101,760 

 cubic cm. for 1200 revolutions. The density of the liquid at a temperature of 

 24 C. was taken as .72, and as 1 volume of liquid gives 180 volumes of gas at 



a pressure of 2\ atmospheres, we have — =-^> — =565 cu. cm. of liquid, or 407 



grammes required for 1200 revolutions of the engines. 



Thus, a theoretical calculation seemed to indicate that a kilogramme of 

 liquid carbonic acid would be an ample supply for a run of two minutes. The 

 experiments were, at first, somewhat encouraging. The speed and apparent 

 power of the engines were sufficient for the purpose, but the length of time 

 during which power could be obtained was limited. 



In L892, 415 grammes of carbonic acid drove the engines of Aerodrome No. 

 3 "nit revolutions in 60 seconds, 900 in 75. and 1000 in 85 seconds, at the end of 

 which time the gas was entirely expended. The diameter of these cylinders was 

 2.4 cm., the stroke of the pistons 7 cm., and the work done, thai of driving a pair 

 of 50 cm. propellers, when taken in comparison with the propeller tests detailed 

 elsewhere, amounted to an effective horse power of about 0.10 for the output of 

 the engine. 



The difficulties, however, that were experienced were those partially fore- 

 seen. The expansion of the gas made such serious inroads upon the latent heat 

 the liquid, that lumps of solid acid were formed in the reservoir, and could be 

 heard rattling againsl the sides when the latter was shaken, while the expansion 

 of the exhaust caused such a lowering of temperature at that point, that the 



