CHEMISTRY. "96 
driving it out through the aperture C (or a). The tube c serves to indicate 
the height of the water in the vessel A, and consequently the volume of gas. 
When the gasometer is filled, the opening C is closed. When the gas 
is required for use it escapes through a tube attached to the right of fig. 5, 
which is provided with a cock. On pouring water into B, and opening the 
cock d, the water will descend to the bottom of A and press upwards against 
the gas. This will then readily flow out on opening the cock of the lateral 
tube. 
It has already been mentioned that oxygen and hydrogen unite in 
proportions of one measure of the former and two of the latter to form 
water, whenever the electric spark is passed through the mixture. A 
mixture in these proportions is known as the explosive gas. The union of 
the two gases takes place with an extraordinary development of heat, and 
in the moment in which watery vapor is formed by the combination so 
sudden an expansion is produced, that large quantities of gas sometimes 
involve serious explosions. The heat generated in this combination is the 
most intense which chemistry can produce; many substances formerly 
deemed infusibie, being readily melted when exposed to this flame. An 
arrangement by which the two gases can be burned together without 
danger is called an oxy-hydrogen blowpipe. Asimple arrangement of this 
kind may be readily understood from what has been said on the subject of 
the gasometer. One gasometer must be filled with oxygen, another with 
hydrogen, and the two so arranged that the escape gas pipes from both 
vessels may stand at an equal height and a little inclined to each other. 
Then on opening the proper cocks in the two, a current of gas will escape 
from each, which being inflamed together or being allowed to pass through 
the flame of a spirit lamp, will produce a heat so great as to melt a wire of 
platinum. Several contrivances may be employed to prevent any danger 
of explosion which might arise from the inflammation of a mixture of the 
two gases. A direct mixture of the gases before combustion would be 
perfectly safe by causing them to pass through Hemming’s safety tube, a 
tube filled compactly and entirely with fine cylinders of wire, so that the 
gas must pass through the exceedingly fine tubes formed by the interspaces 
between the cylinders. Gurney’s apparatus of safety may also be used. 
4. Apparatus for Combining Solid and Liquid Elements. 
As has already been remarked, there are only two elementary bodies 
which are liquid at ordinary temperatures; these are mercury and bromine. 
By far the greater number are solid. With respect to the latter we may 
say in general that one solid element does not combine with another. The 
condition of aggregation of bodies that are to combine together must be 
liquid or gaseous, a condition to which solids must be brought. Consequently 
we may consider the combinations of liquids and solids under one head, 
provided the solids be supposed to be rendered liquid by heat. Setting 
aside the gases, we have as non-metallic elements, boron, bromine, iodine, 
453 
