The Art of Lead Burning / A practical treatise explaining the apparatus and processes.

by C. H. Fay

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.

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.

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.