CONNECTING THE APPARATUS.
We now assume that the generator is charged and the rest of the
apparatus is finished and ready for use, so we will proceed to connect
it up ready for a trial.
About 30 feet of ¼-inch heavy rubber tubing should be procured. This
hose should be heavy enough to allow of its being pulled around without
kinking and shutting off the supply of gas. A piece of this hose 5 feet
long should be slipped on the gas cock M on the generator, shown in Fig.
1, and then slipped over the gas inlet tube of the scrubbing cup _n_.
One must be sure that this is connected to the gas inlet tube, which is
the tube that dips under the water in the scrubbing cup.
With another 5-foot piece of hose connect the gas outlet of scrubbing
cup _o_ to the right hand cock on the mixing fork _f_. Always connect
the gas on the same side so as to avoid confusion of cocks. Then with a
10-foot piece of hose connect the air cock on the air holder _p_ or
bellows to the remaining cock on the mixing fork _g_. An 8-foot piece
should be connected from the gas outlet on mixing fork _e_ to the blow
pipe _i_.
These tubes must fit tight to prevent any possible leak of gas, and if
they do not they should be tightened on with pieces of wire. The
remaining piece of hose can be used to connect the air pump C to the air
inlet cock _s_ on the air holder, but if the bellows are used this will
not be needed.
Now place in the scrubbing cup a half dozen pieces of blue vitriol, or
copperas, as it is commonly called. Then pour in clear water until it
flows out of the trap screw _z_. This screw can be made tight by using
for packing a piece of wicking which has been saturated with tallow.
After preparing the apparatus as above, refer to the cut of the complete
apparatus and compare the connections on the cut with those made from
the above directions, to make positive that they are right. If they
agree, the apparatus is now ready for use.
Testing the Apparatus.
It is necessary to test the generator for leaks, as a small blow hole
may sometimes be left in some of the seams or the cocks or cleaning
screws become defective.
To do this, first close the gas cock on the top of the gas chamber and
make up the cleaning and charging screws, which must be set on a bed of
soft putty. Then fill the acid chamber full of hot water, first
measuring the water so as to ascertain just how much solution is
required in proportion to the amount of water, as it takes the same
quantity at all times. Allow it to stand for a few moments, then mark
the water line with a pencil or nail, when it should be left standing
for an hour. The water should stay at the mark indicated for an
indefinite time. If it sinks during this test it shows that there is a
leak in the generator and it must be located and repaired.
[Illustration:
_Fig. 15.—Mixing Fork._
]
To locate the leak the gas cock should be opened and the water allowed
to run into the gas chamber. If this does not show the leak, force the
water back into the acid chamber, which is done by attaching the air
pump to the gas cock. Then taking a piece of soap and making a stiff
lather, daub it over the cocks and cleaning and charging screw. When the
leak is found the escaping air will cause bubbles to be blown. If the
leak does not become apparent after the above process, the side boards
of the generator should be taken off and the operation repeated on the
seams.
Under no circumstances must the apparatus be left until there is
absolutely no doubt as to its being perfectly tight, as a slight leak
would be likely to cause a disastrous explosion and injure or probably
blind the operator. Flying vitriol is not a very pleasant thing to get
in one's eyes.
The apparatus should be frequently tested in this manner: Before drawing
off the water it is desirable to learn what amount of gas pressure there
will be when the generator is charged, so that the pressure of air and
gas can be equalized. The mathematical rule for this is to multiply the
head in feet by 0.434, and the result will be the pressure in pounds; or
an approximate way of determining the pressure is to allow ½ pound
pressure for every foot of head. For example: The hight of liquid in the
generator measured from the bottom of the acid supply pipe to the top of
the water or acid line, when at its highest level, would be 3 feet.
Allowing ½ pound for every foot in hight would give a pressure of 1½
pounds, which is slightly in excess of the mathematical rule, which is 3
× 0.434 = 1.302, or 1 pound 4 ounces, but to be accurate it is well to
attach a mercury gauge to the gas cock. Note the hight of the column of
mercury. Then attach the gauge to the blast apparatus, and if the
floating air holder is used, sufficient weight must be put on the top of
air holder to raise the column of mercury to a point not quite as high
as is indicated by the generator. These weights can then be weighed and
a similar weight made of lead to correspond, which can be kept for
permanent use. If the bellows are used, the size specified should be
obtained, and the pressure will be all right for this size generator
without further trouble. If the air holder indicated by Fig. 8 is used,
all that is necessary is to make the hights of the water line in both
generator and air holder equal, and the pressure must be the same.
[Illustration]
_Fig. 16._ _Fig. 17._
_Mixing Forks._
The reason that the air pressure should not be heavier than the gas
pressure is that if the air were the stronger there would be danger of
the air working back into the gas tube and causing an explosion in the
tubes; consequently it is well to note this point carefully. Many lead
burners will say that the pressure of air is of no consequence, and all
that is required is a sufficient supply; but my experience and
experiments have convinced me that when the pressures of air and gas are
nearly equal the best results are obtained.
The Mixing Fork and Blow Pipe.
The mixing fork and blow pipe can be made in any plumbing shop and
should be made of the smallest size pipe available.
[Illustration:
_Fig. 18.—Blow Pipe and Tip._
]
To make the mixing fork, purchase two ⅛-inch female hose end gas cocks
and 2 feet of ⅛-inch iron pipe size brass tubing. Take a piece of the
tubing 12 inches long, cut a regular iron pipe thread on each end, then
bend it over a mandrel stake or a piece of 4-inch soil pipe into a half
circle, as shown in Fig. 15, so that the ends will come about 4 inches
apart. In the center of this piece drill a ⅛-inch hole, _a_. Then cut
from the remaining piece of tubing a piece 3 inches long. Solder, or,
better yet, have this piece brazed on to the bent piece at _a_, taking
care that no solder can run in and partially stop the hole _a_. Then
screw the two ⅛-inch gas cocks on the ends _b_ and _c_. This will
complete the mixing fork; or this fork can be made by bending a piece of
pipe at an angle, as shown in Fig. 16; then cut another piece equal in
length to the bent piece from the angle _e_ to the end. One end of this
piece must be filed to fit the piece _d_. A hole can then be drilled at
_e_. Threads must be cut on these ends, after which they can be brazed
together. Or a good fork can be had by using a special casting. This
casting is used for and is known as a beer switch, and can be purchased
of any dealer in bar supplies, Fig. 17. The same pattern and size of
cocks can be used for this fork as previously described. Neither of
these mixing forks has any advantage over the other, but three styles
are given, as possibly one may be easier to make than the other. Iron
pipe may be used instead of brass if desired.
To make the blow pipe, take the remaining piece of tubing and cut a
thread on one end. As the other end slips into the hose, it does not
need a thread. The thread end must then be bent at right angles to the
tubing, as _c_, Fig. 16. This can be done by boring a hole in a block of
hard wood just large enough for the tubing to enter, and 1½ inches deep.
Trim off the sharp edge of this hole so as not to kink the pipe in
bending. The end of the tube can then be inserted in this hole and bent
to the desired shape, as shown. This completes the blow pipes with the
exception of the tips, of which you should have three sizes, drilled as
follows: One for heavy lead, 3-32; one for medium weight, 2-32, and one
for very light sheets, 1-32. These tips are made of small pieces of cast
or turned brass, preferably with a milled shoulder, so as to facilitate
removing with the fingers. Probably the easiest way to get these tips is
to make a pattern out of wood and have several of them cast. They can
then be drilled and tapped to any desired size, or they can be cut from
a round bar of brass or copper, filed or turned to a point, then drilled
and tapped. The dimensions and particulars can be had from B in Fig. 18
without further description being necessary. A common blow pipe, such as
is used with the alcohol torch, can be used for practicing on light
sheets. But the beginner is advised to procure the blow pipe and a set
of tips described in Fig. 18 before attempting to burn any heavy lead.