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

by C. H. Fay

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.

CHAPTER VII.
CHARGING THE GENERATOR.

After making sure that the generator is perfectly tight we will proceed to charge it. After removing the 4-inch charging screw take 15 pounds of commercial spelter, which has been broken up with a hammer into pieces about 2 inches square, and place this in the gas chamber, distributing it as evenly as possible over the perforated bottom. This is done so that the zinc will expose all the surface possible to the action of the acid, and must be observed in order to obtain the best results. Do not put any pieces of spelter into the generator that are small enough to drop through the perforated bottom, for if they do they will be likely to generate gas, which will give overpressure and blow gas out through the acid chamber. This can do no harm unless close to a light, but it is very annoying to have acid blown all over the generator. The charging and cleaning screws must be screwed up tight. After closing the gas cock on the generator take the quantity of water (less one-seventh) that was found to be necessary when testing the apparatus, and pour this into the acid chamber.

Mark the water line and watch it for a few moments to make sure that everything is tight. Then take of sulphuric acid a quantity equal to one-seventh of the water used, and pour that into the water in the acid chamber. It will diffuse itself through the water and thoroughly mix. Experience has taught me that acid mixed in any proportion stronger than seven parts of water to one part of acid does not act as quickly as when mixed in the proportion mentioned. The reason for this is that the strong acid simply coats the zinc with a deposit or scum of sulphate of zinc, which is soluble in water, but is not soluble in acid. Therefore, if the acid is diluted with water to the above mentioned proportion the water readily dissolves the sulphate and allows the acid to act freely on the zinc.

This sulphate falls to the bottom of the gas chamber and if allowed to accumulate causes the clogging mentioned later. The beginner will observe from the explanation that the generator cannot be crowded by making the solution strong. It sometimes occurs that the vitriol seems to be stronger than usual, and then again the reverse is also true. Good vitriol should be almost as thick as cutting oil, and will work very quickly. Care must be taken in pouring it into the generator to prevent spattering. This is best avoided by having a quart measure made of lead for this purpose. It should also be borne in mind that the acid should always be added to the water, never the water to the acid, as this mixture always generates heat, and the result would be similar to adding water to hot lead.

Automatic Action of the Generator.

The generator works best while hot. The gas cock on the generator should now be opened and the mixture allowed to flow into the gas chamber until it spurts out of the gas cock, which must then be closed. By this action all the air in the gas chamber is expelled, leaving it free to generate pure gas at once. This is a sure method of exhausting the air in the gas chamber. The acid then attacks the zinc, causing it to decompose the water and free the hydrogen contained in the acid.