Chromate of Zinc (ZnCrO4) is used in calico-printing, and there is also in commerce a basic chromate known as zinc yellow. Zinc green, or Rinman’s green, is a beautiful innocuous colour, formed by igniting a mixture of dry zincic and cobaltous carbonates.
The use of zinc vessels in the preparation of foods may occasionally bring the metal under the notice of the analyst. When exposed to a moist atmosphere, zinc becomes covered with a thin film of oxide, perfectly insoluble in ordinary water; but, if the water should be charged with common salt, a considerable quantity may be dissolved. It may generally be laid down as a rule that the solvent power of water on zinc has a direct relation to the chlorides present, whilst carbonate of lime greatly diminishes this solubility.[949]
[949] Ziurek, indeed, found in a litre of water contained in a zinc cistern no less than 1·0104 grm. of zinc, and the same water showed only 0·074 grm. of common salt to the litre.—Vierteljahrsschr. für gericht. Medicin, 1867, Bd. 6, p. 356.
Milk may become contaminated by zinc; for, it is a matter of common knowledge, that milk contained in zinc vessels does not readily turn sour. This may be explained by the zinc oxide combining with the lactic acid, and forming the sparingly soluble lactate of zinc 2(C3H5O3)Zn + 3H2O, thus withdrawing the lactic acid as fast as it is formed, preventing the coagulation of the casein. With regard to this important practical subject, MM. Payne and Chevallier made several experiments on the action of brandy, wine, vinegar, olive oil, soup, milk, &c., and proved that zinc is acted on by all these, and especially by alcoholic, acetic, and saline liquids. M. Schaufféle has repeated these experiments, and determined the amount of zinc dissolved in fifteen days by different liquids from a galvanised iron as well as a zinc vessel.
The amount found was as follows:—
| The liquid from the zinc vessel, grms. per litre. | The liquid from the galvanised iron vessel, grms. per litre. | |||
|---|---|---|---|---|
| Brandy, | 0 | ·95 | 0 | ·70 |
| Wine, | 3 | ·95 | 4 | ·10 |
| Orange-flower water, | 0 | ·50 | 0 | ·75 |
| Vinegar, | 31 | ·75 | 60 | ·75 |
| Fatty soup, | 0 | ·46 | 1 | ·00 |
| Weak soup, | 0 | ·86 | 1 | ·76 |
| Milk, | 5 | ·13 | 7 | ·00 |
| Salt water, | 1 | ·75 | 0 | ·40 |
| Seltzer water, | 0 | ·35 | 0 | ·30 |
| Distilled water, | traces. | traces. | ||
| Ordinary water, | traces. | traces. | ||
| Olive oil, | none. | none. | ||
§ 862. Effects of Zinc, as shown by Experiments on Animals.—Harnack, in experiments with sodium-zinc oxide pyrophosphate, has shown that the essential action of zinc salts is to paralyse the muscles of the body and the heart, and, by thus affecting the circulation and respiration, to cause death; these main results have been fully confirmed by Blake, Letheby, and C. Ph. Falck. For rabbits the lethal dose is ·08 to ·09 grm. of zinc oxide, or about ·04 per kilogrm. The temperature during acute poisoning sinks notably—according to F. A. Falck’s researches on rabbits, from about 7·3° to 13·0°. Zinc is eliminated mainly by the urine, and has been recognised in that fluid four to five days after the last dose. It has also been separated in small quantity from the milk and the bile.
§ 863. Effects of Zinc Compounds on Man—(a) Zinc Oxide.—The poisonous action of zinc oxide is so weak that it is almost doubtful whether it should be considered a poison. Dr. Marcett has given a pound (453·6 grms.) during a month in divided doses without injury to a patient afflicted with epilepsy; and the workmen in zinc manufactories cover themselves from head to foot with the dust without very apparent bad effects. It is not, however, always innocuous, for Popoff has recorded it as the cause of headache, pain in the head, cramps in the calves of the legs, nausea, vomiting, and diarrhœa; and he also obtained zinc from the urine of those suffering in this manner.[950] Again, a pharmacy student[951] filled a laboratory with oxide of zinc vapour, and suffered from well-marked and even serious poisonous symptoms, consisting of pain in the head, vomiting, and a short fever. It must be remembered that, as the ordinary zinc of commerce is seldom free from arsenic, and some samples contain gallium, the presence of these metals may possibly have a part in the production of the symptoms described.