It will be argued in Chapter III. that a rising
holder is always preferable to one constructed on the displacement
principle. The pressure (d) at the burners may be taken at 4
inches of water as a maximum, the precise figure being dependent upon the
kind of burners--luminous, incandescent, boiling, &c.--attached to the
main. The pressure (_b_) also varies according to circumstances, but
averages 2 or 3 inches. Thus a pressure in the generator exceeding that
of the atmosphere by some 12 inches of water--_i.e._, by about 7
oz., or less than half a pound per square inch--is amply sufficient for
every kind of installation, the less meritorious generators with
displacement holders only excepted. This pressure, it should be noted, is
the net or effective pressure, the pressure with which the gas raises the
liquid in a water-gauge glass out of the level while the opposite end of
the water column is exposed to the atmosphere. The absolute pressure in a
vessel containing gas at an effective pressure of 12 inches of water is 7
oz. plus the normal, insensible pressure of the atmosphere itself--say
15-1/4 lb. per square inch. The liquid in a barometer which measures the
pressure of the atmosphere stands at a height of 30 inches only, because
that liquid is mercury, 13.
Pages:
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143