160 
POPULAR SCIENCE REVIEW. 
Except this last experiment, which requires an additional 
pressure on the gas, all the foregoing experiments can be re- 
peated merely by attention to the shape and size of the burner, 
having the stopcocks and gas passages as widely open and free 
as possible, and using the gas under the greatest pressure 
obtainable from the main ; hence the dusk of the evening, when 
this pressure appears to be at its maximum, is the best 
time for repeating these experiments. The same burner may 
give a flame not sensitive at one time of the day, but very sensi- 
tive at another, and the pressure may become so great that the 
flame may again lose its sensitiveness. Other burners, as the 
batswing, require a greater pressure than that which is given 
from the gas works to make them sensitive. 
To obtain, therefore, the most complete results we must our- 
selves increase the pressure of the gas. This can be done by 
filling a gas-holder or gas-bag with coal- 
gas, and forcing the gas therefrom ; or, 
lacking these, a useful substitute can be 
found in an india rubber air pillow, which 
must have its screw replaced by a stopcock. 
Through a flexible tube the gas can be con- 
ducted from its reservoir to the burner, 
which may be held fast in a clip, or other 
support. All that is now necessary is to 
bring the gas very near to the point at 
which it gives a roaring noise as it issues 
from the burner. This is accomplished by 
altering the weights on the bag, or adjust- 
ing the stopcock 
of the holder. 
The general ar- 
rangement of 
the apparatus is 
shown in Fig. 3. 
Under this 
increased pres- 
Fig. 3. 
sure other burners can be used beside the shape shown in fig. 1 . 
A circular iron nipple can be employed, or still better, a burner 
made of steatite or silicate of magnesia, a substance which has 
the advantage of expanding so slightly by heat, and being un- 
corroded by use, that practically the size of the orifice remains 
always the same. Selecting one of these steatite burners having 
a single circular orifice, *046 inch in diameter, or just admitting 
No. 19 wire, and igniting the gas which is urged from it, a 
for further information, and, I need hardly add, what is sure to he the most 
lucid exposition of the subject of u Sensitive Flames.” 
