ITPOiV SOjVIE op the PHENOMENA OP COMBUSTION. 
639 
tlie velocity of the current of air is only just sufficient to prevent the escape of uncon- 
sumed fuliginous matter ; in other words, a maximum of light is obtained from a gas- 
flame, other things equal, when that flame is maintained just below the smoMng'point. 
This condition of maximum luminosity was carefully secured in aU the following de- 
terminations, by regulating, by means of the stopcock d, the admission of external air, 
and thereby the velocity of the current in the chimney J, the cock c being wide open, 
^'^'hen, however, the experimental flame was burning at atmospheric pressure, the cock 
d was removed, leaving a large aperture for the admission of air, whilst the current 
through the chimney was regulated by the cock c. The extremity of the gas-delivery 
tube e was narrowed to a cu’cular aperture 1'5. millimetre in diameter (about 
inch), thus forming a burner of such magnitude as not only to prevent the gas from being 
discharged from e uith more than the smallest possible pressure, but also to render the 
difierence of pressui’e between the gas in e and the air in the glass cylinder practically 
the same in all the observations. In the early stages of the experiments considerable 
annoyance was experienced by the water produced in the combustion condensing in the 
tubes leading from the chimney I to the reservoir F, whilst the cock c and the caoutchouc 
connector between c and k became inconveniently heated. These difficulties were 
removed by enclosing the caoutchouc joint with a tin jacket {1), which was kept filled with 
hot water, and by providing two double-necked bottles (only one of which, m, is shown 
in the figure), immersed in vessels of cold water, for the completion of the refrigeration 
and the collection of the condensed water, m was conveniently connected with F, and 
the latter with the air-pump, by means of vulcanized india-rubber tubing of sufficient 
substance to resist compression, when rendered nearly vacuous internally. 
Each series of experiments was made in the following manner : — The standard flame 
B was lighted, and its rate of consumption regulated to about ‘6 or -7 cubic foot per 
hour. The absolute amount of gas consumed by this flame was obviously not material, 
provided that its rate of consumption and conditions of combustion did not vary during 
the continuance of any one series of experiments. This constancy in the rate and con- 
ditions of combustion was secured by the governor A. The cock c being closed, and the 
pressure in F reduced to about 6 inches of mercury, the cock d was removed, c slightly 
opened, and the experimental flame ignited by the introduction of a small taper through 
the aperture from which d had been removed : the latter cock was then replaced, and 
gradually turned so as to cut off all but the necessary supply of air, whilst c was at 
the same time gradually opened so as to equalize the pressure in the glass cylinder and 
m F. W ith this diminution of pressure in the glass cylinder it was of course necessary 
simultaneously to reduce the size of the aperture through which the gas passed from 
the meter to the burner ; and this was effected by the micrometer cock ^. The pressure 
in F was now allowed to rise until it reached the lowest point at which a series of ob- 
servations was to be made : at this point it was then maintained constant by the steady 
working of the air-pump. The consumption of gas in the experimental flame having 
been now accurately adjusted to -65 cubic foot per hour, and all extraneous light excluded 
