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—Make this flux at home from finely snipped new sheet-zinc and pure hydrochloric or muriatic acid. (This is sufficiently cheap at any working druggist’s stores, and infinitely preferable to the contaminated oil-shop quality known as “spirits of salt.”) Stand the acid outdoors in a stoneware crock, add the zinc cuttings a few at a time at first, and when the first violent ebullition moderates, put in the rest. Be sure to provide an excess of metallic zinc, observing that a quantity remains undissolved after all chemical action ceases. Leave the metal in the liquor for twelve hours (covering the crock with a pane of glass), then decant and filter into a wide-mouth glass jar of handy size. Do not add water to the concentrated zinc chloride solution; dilution is sometimes recommended, but should never be done; the heavy, slightly syrupy, water-bright liquor should be used as it is. The alleged “cleaning” qualities of this chloride can scarcely be admitted to exist, and its principal function is to shield the surfaces of the work from oxidation; this it fulfils by the formation of a viscid glaze on the heated metal when the salt reaches its anhydrous (waterless) condition by evaporation. The addition of water to the flux, therefore, only uselessly prolongs the period occupied by evaporation, and wastes heat.

Always remove all trace of flux from finished work, first by soaking in water, and afterwards by washing with soda, soap, and water. Otherwise, there is the risk of the work being corroded.

Special “soldering solutions,” obtainable ready prepared, should not be used in preference to zinc chloride made as before explained or to the well-known paste fluxes.