Pour a small handful of the zinc cuttings into the acid. The acid will attack them at once and a strong bubbling action will result. When the bubbling action dies down add more zinc cuttings—about every fifteen minutes. When the acid shows no sign of attacking the zinc as it is added, the acid is said to be “killed” and the soldering fluid is made. It may be used at once if necessary, but it will be much better if it is allowed to stand over night with the zinc residue left in it. It is then strained through a piece of muslin cloth into another cup or jar and the fluid is ready for use.
Soldering fluid may be kept in a wide-mouthed glass bottle or a marmalade jar; either vessel must be tightly corked when not in use. This soldering fluid may be used as a flux for any soft soldering operation in place of the soldering paste, but it is not as satisfactory a flux for the tin can work as the paste. The best use for it in connection with the tin can toys is to keep it to dip the point of the hot copper in occasionally to clean the tinning at the point of the copper.
While the prepared soldering paste is best for all soldering operations connected with the tin work, other fluxes may be used if nothing better is at hand. These are resin, olive oil, cottonseed oil, automobile lubricating oil, and paraffin; but these fluxes are not very satisfactory in inexperienced hands. The soldering paste is best for all soldering operations.
CHAPTER V
Soldering (Continued)
PREPARING A JOINT FOR SOLDERING—CLEANING AND SCRAPING—SOLDERING A PRACTICE PIECE—SOLDERING THE HANDLE TO THE BISCUIT CUTTER—A SECOND PRACTICE PIECE—ANOTHER METHOD OF APPLYING SOLDER
Cleaning and Scraping.—If the copper is thoroughly tinned and the heater and materials are ready for use as described in [Chapter IV], then several practice pieces should be soldered together before attempting a joining on any real work you may have ready to solder.
If the tin is bright and clean, it need not be scraped at the joint where the solder is to go. Rusty spots should be scraped bright if in the path of the solder. Paper, labels or paint must be cleaned away. If a can has been well rinsed with hot water when the contents are emptied, it will present no difficulties to the soldering, but a can that has been emptied but not rinsed presents a more difficult surface to solder; particularly tomato, fruit, or condensed milk cans. This, of course, applies only to the inside of these cans. Tobacco, coffee, cocoa, tea cans and the like offer no resistance to the solder without washing. The yellow lacquer used to line some cans need not be scraped off. Solder will adhere well to tin so treated, but paper, paint, etc., must be scraped from the path of the solder. The scraped part need only be a quarter of an inch in width on each side of the joint; the rest of the paper labels or paint will be removed in the hot lye bath used before painting the can.
The scraping may be done with an old knife, or a regular scraper furnished by the dealer in tinners’ tools as illustrated on [page 202, Chapter XXI].