THE APPARATUS.
The apparatus used for lead burning is illustrated in Fig. 1. It
consists of a gas generator, A; an air holder, B, and pump, C; mixing
fork, _e_, and necessary cocks, _f_ and _g_; combined scrubbing cup and
fire trap, _h_; blow pipe and tips, _i_.
The generator consists of an acid chamber, _j_, and a gas chamber, _k_.
These are connected with an acid supply pipe, _l_, which conducts the
acid from the acid chamber to the gas chamber, and also serves as a
balance pipe.
This feature makes the generator automatic in its action, for as soon as
the gas in the gas chamber gets up sufficient pressure, the acid in the
gas chamber _k_ is driven slowly back through the acid supply pipe _l_
and up into the acid chamber _j_, where it is held until gas is used.
When the acid descends and submerges the zinc more gas is generated,
replacing that which has been used. This form of generator will never
blow acid like the floating generator.
The requirements of a hydrogen generator for lead burning are that it
should be safe, economical and automatic in its action. It must be so
constructed that it will generate gas enough to keep the supply
constant, and deliver it at sufficient pressure to keep the flame
steady. It must also be provided with a combination fire trap and
scrubbing cup. This will prevent the explosion of the generator by
firing the gas in the hose. This trap must be partly filled with a
solution of blue vitriol to act as a precipitation cup. (This is treated
under the head of “Scrubbing Cup.”)
The chief danger with an apparatus of this sort is its liability to
accident by the careless use of the gas, and, as a mixture of hydrogen
and air is very explosive, great care must be taken to exhaust all the
air in the generator and tubes before attempting to light the gas at the
blow pipe. The only way to make sure that the air is exhausted is to
test the gas, as described under the head of “The Flame and Its
Management.”
A Few Cautions.
It is a very sensible idea to keep spectators away from the generator,
as they are very apt to strike matches or tread on the tubes, in spite
of warnings to be cautious, for if there should be a leak, even so
slight as to be hardly detected, it would cause a violent explosion, and
as hydrogen is both odorless and colorless, this could easily happen
without being noticed. This is probably the origin of the apparent
secrecy with which a lead burner usually surrounds himself.
If an explosion should occur in the tubes and they should catch fire,
the operator must have presence of mind enough to reach the gas cock on
the generator and close it. If gas explodes in the generator, all that
can be done is to dodge the flying pieces and make a new generator. If
such an incident should occur and vitriol should spatter on the person
doing the work, or his assistant, a solution of bicarbonate of soda or
common washing soda should be at once applied to the wounds. If that
cannot be procured, grease or oil of some kind should be used without
delay, rubbing it on the spots where the acid burns, and this will
neutralize the acid and so prevent it doing further damage. There should
be no trouble of this sort in the hands of a careful workman. The
watchword should be, “Test the gas before using.” If this is done,
explosions will never occur.