306 
ON THE COMBUSTION OB" GAS FOH ECONOMIC PURPOSES. 
Paraffin oil . . 
265 
grs. 
. . 7T1 . 
522 
grs 
Sperm oil . . 
686 
33 
. . 10-00 . 
-. 960 
55 
Colza oil . 
648 
33 
. . 9-01 . 
. 1008 
55 
Paraffin candles . 
122 
55 
. . 1-46 . 
.• 1171 
35 
Sperm „ 
132 
53 
. , T35 
. 1440 
55 
Wax „ 
168 
53 
. . 1-43 . 
. 1652 
33 
Stearic „ 
140 
53 
. . 1-13 . 
. 1732 
53 
Composite „ 
144 
55 
. . 1-08 . 
. 1858 
35 
Tallow „ 
145 
55 
. . 0-83 . 
. 2542 
33 
With regard to the value of other illuminating agents, as the magnesium light, the 
oxhydrogen or Drummond light, and the electric light, little can be said, as they vary 
£0 much with the consumption of the material. 
In the case of the magnesium light, I find that when a wire the 100th of an inch in 
diameter is doubled and twisted, it burns at the rate of 2•I grains per minute, and gives 
the light of about 69 standard sperm candles ; an ounce of the wire, therefore, is equal 
in light-giving power to rather more than 3|^lbs. of sperm candles. The power of the 
Drummond, or oxyhydrogen light, varies with the combustible used. With 
Coal gas and air it is equal to 19 
„ „ oxygen „ 29 
Alcohol „ „ „ 69 
Ether „ „ „ 76 
Hydrogen „ „ 153 
candles. 
5 ? 
?? 
5? 
And the power of the electric light varies from 650 candles to 144-1, the average being 
about 1000. 
All these agents are expensive, and they give alight which is characterized by inten¬ 
sity rather by quantity but as the light is pure as well as powerful, it is frequently used 
for signals and for photographic purposes, and also for theatrical illustrations. 
I now pass to a very interesting part of our subject, namely the cause of the marked 
differences in the colour of the flames of different substances; and in order that you 
may perceive the reason of this, let me remind you that a pure white light, with all 
the colours of the spectrum, is never obtained but by the intense ignition of solid or 
molten matter. This is so with the phosphorus flame, and with the magnesium, the oxy¬ 
hydrogen, and the electric light. In all these cases there are particles of concrete solid 
matter in a state of intense ignition, but in the case of coal gas, and in that of other 
burning hydrocarbons, the light is never pure unless it is intensified by very energetic 
combustion. The reason of this is that the particles are only heated to the point of yellow' 
whiteness ; for Dr. Draper has sho'vn that, acording to the temperature, an ignited solid 
(as a spiral of platinum heated by the galvanic current) passes through all the tints of 
the spectrum from red to white, according to the intensity of the heat; and these tints 
and temperatures are somewhat as follows :— ^ 
Very dull red . 
. . . about 
970 
Cherry red . . 
• • • • ^ 
1500 
Full red . . 
• . . 55 
2000 
Dull red, white, 
Yellow white . 
or orange „ 
3000 
• • • 53 
4000 
Greenish-white 
• • • 53 
5000 
Bluish-white . 
• • • 35 
6000 
Perfect w'hite . 
• • • 55 
7000 
Fahrenheit. 
?? 
53 
35 
55 
If, therefore the temperature of combustion is not sufficiently high, the light is never 
pure. This is especially so with the creamy lagging flame of uuderburnt gas, and wutli 
the smoky flame of hydrocarbons rich in carbon, as benzole, turpentine, and paraffin; 
but if the combustion of these flames is intensified by a proper supply of air, the tempe¬ 
rature of the ignited carbon is increased, and the light becomes purer and purer, so that 
when it is thrown upon coloured objects it displays the tints in a more or less perfect 
manner. Such a flame, when examined with the prism, gives a spectrum like that of 
solar light, with all the tints of the rainbow. This is the specialty of pure light from 
