1907.] on Flame in Gas and Petrol Motors. 509 



ment, so far as practical matters are concerned ; so that now, over 

 two million horse-power of stationary gas engines operated by flame 

 are in use in the world. It is difficult to form an estimate of the 

 power of motor car engines in use, l>ut prol)ably it now exceeds a 

 million horse-power. 



Although great progress has been made in the practical control 

 and utilisation of flame and gaseous explosions, for the purpose of 

 producing motive power, little is as yet known as to the actual pro- 

 perties of the flame working fluid so utilised. In this branch of work 

 science so far has made but little progress, and our knowledge of the 

 properties of air and other gases at high temperatures is of a some- 

 what fragmentary nature. Science still requires to investigate the 

 properties of gases at high temperatures, in order to fill the gap in 

 our knowledge at the upper end of the scale, which Sir James Dewar 

 has so }d)ly filled at the low^er end. Accordingly, for the present, it 

 is not possible to formulate a complete theory of the internal com- 

 bustion motor, in the absence of knowledge of the properties of the 

 gases constituting its working fluid at the very high temperatures 

 attained. The subject is a difficult one, and involves not only the 

 statical properties of these gases, but it requires a knowledge of the 

 conditions and rate of chemical combinations occurring in minute 

 fractions of a second, and the conditions of dissociation of compounds 

 such as carbonic acid and steam at high temperatures under vai-ying 

 temperatures and pressures. Our knowdedge, for example, of the 

 dissociation curves proper to steam or carbonic acid, is in the vague 

 qualitative state. It is known that under certain circumstances some 

 dissociation occurs ; but no accurate quantitative knoAvledge exists- as 

 to the amount of dissociation under any given conditions of tempe- 

 rature and pressure, either alone or in mixture with other gases. 

 Notwithstanding our present ignorance on this subject, many dis- 

 tinguished investigators have given it some attention. Bunsen 

 attacked the problem in 1866. Fig. 5 is a drawing of the apparatus 

 used by him. Here is arranged a small glass tube A which you see with 

 a valve B, weights C to apply pressure to the valve, platinum points D D 

 between which the electric spark could be passed the whole length of 

 the tubular vessel. The vessel was filled with various explosive mix- 

 tures, and ignited by the spark. The valve was loaded until it just 

 blew off. This blow-off pressure was considered to be the maximum 

 pressure- produced by the explosion. Bunsen made many experiments 

 in this way. He considered his explosive mixture to be an air 

 thermometer, with a varying volume, and after allowing for the 

 variation due to chemical combination, he was able to calculate from 

 his pressures the maximum mean temperature of the mixture. As a 

 result of his experiments, Bunsen discovered that in none of the 

 gaseous explosions investigated by him could he ol)tain the maximum 

 pressures which he expected from the total heat of the mixture 

 present, and the known specific heat of the products of combustion 



