This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Metallic contamination of carbonated beverages is a frequent occurrence. Poisonous metals are apt to be found as impurities in certain commercial organic products, being accidentally introduced during the process of preparation. In carbonated drinks the sources of metallic impurities are defective apparatus. The objectionable metals most commonly occurring are lead, copper and zinc. Cases are not rare where the presence of these metals in the beverage has been exceedingly harmful. We have in a former Chapter referred to the corrosive action of carbonated water exerted upon lead, and warned the bottler to use no vessels, tubes, pipes, solderings, syphon-heads nor patent stoppers, containing these contaminating metals, or glazed earthenware vessels with a lead compound for syrups. Beverages were found impregnated with copper in every case in which tin-washed copper fountains were used. Verdigris originates from unlined or brass syrup gauges, which are scarcely if ever cleansed. Metallic impurities, especially lead, may enter into a beverage by using contaminated citric or tartaric acid, as formerly mentioned. The quantity of lead found in samples varied from 0.07 of a grain to 0.5 grain to the gallon; in some only "traces" of the metals are found.
We append a few tests for metallic contaminations, which the bottler may easily apply, and thus examine his beverages.
1. A very delicate test is by the direct addition of a small quantity of hydro-sulphuric acid. This is applicable where a solution is to be tested for lead only. The hydro-sulphuric acid produces a black precipitate, if lead is present in large quantities; if in small quantities only, a brownish tint to a dark coloration. 2. In testing carbonated waters for lead with sulphuretted hydrogen, the possible presence of tin and copper must not be lost sight of.
Mr. A. W. Blyth has announced that cochineal is one of the most delicate tests he has found for the presence of lead. The test is a one per cent, solution of cochineal in proof-spirit. Ten drops of this is added to a fluid ounce of the water contained in a white porcelain dish. If the water is free from lead the color is simply a dilution of the pink tint; but if it contain but one seven-hundred-thousandth part of lead the tint will be a purplish pink, and if it be as much as one seventy-thousandth part it will become a purple blue. Compare also the tests for lead in water on page 25 and following.
Evaporate not less than a quart until reduced to about an ounce, acidulate very slightly with acetic acid, and apply the following tests to three separate portions: 1. Add excess of ammonia water; no blue color should be evident. 2. Add two drops of a dilute (ten per cent.) solution of potassium ferrocyanide (yellow prussiate); no red-brown precipitate should appear upon standing half an hour. 3. Into the liquid drop a bright steel needle; after an hour's immersion no coating of metallic copper should be visible. The copper precipitated on the iron will pass into solution, and may be detected by acidulating the ammoniacal liquid with acetic acid and adding potassium ferrocyan-ide, when a purple or brownish coloration will be produced, if a trace of copper be present. These tests are very delicate. Compare also tests for copper on page 27.
The ordinary test for zinc is with an alkaline sulphide. A more satisfactory test is one in which the solution to be tested for zinc is rendered ammoniacal, heated to boiling, and potassium fer-rocyanide added, when a white precipitate will be produced if the merest trace of zinc be present. Compare also test for zinc on page 27.