[858] L’Union pharmac., xvii. 81.
[859] Arch. de Pharm., 1853, cxxvi. 67.
Lehmann has made some useful researches on the amount of copper taken up by fats under different conditions. 100 c.c. of strongly rancid fat dissolved in fourteen days 8·7 mgrms. of copper; but when heated to 160° for one hour, and then allowed to stand, a similar amount was found. Some rancid butter was rubbed into a brass bowl of 90 c.c. capacity, and then allowed to stand for twenty-four hours; the butter became of a blue-green colour. Into this dish, thus partially attacked by fatty acids, 50 c.c. of rancid butter was poured in a melted condition, and allowed to stand for twenty-four hours. The amount taken up was found to be equal to 10 mgrms. of copper for every 100 c.c. of fluid butter.
Hilger found a fatty soup, which had stood twelve hours in a clean copper vessel, to contain 0·163 per cent. copper. According to Tschirch, the easiest fatty salt to form is the oleate, hydrated copper oxide dissolving in oleic acid with great ease, and even copper oxide dissolving to some extent; the palmitate and the stearate are not so readily produced; hence the amount of copper dissolved is greater in the case of olive oil and butter (both rich in oleic acids) than in the case of the firmer animal fats. Acid solutions, such as clarets, acetic acid, vinegars, and so forth, as might be expected, dissolve more or less copper. The amount likely to be dissolved in practice has been investigated by Lehmann. He steeped 600 square metres of copper sheeting or brass sheeting in vessels holding 2 litres of acid claret; the sheets were in some of the experiments wholly immersed, in others partly so. More copper was dissolved by the wine when the copper was partly immersed than when it was wholly immersed; and more copper was dissolved from brass sheeting than from pure copper sheeting. With a sheet of copper, partly immersed, claret may contain as much as 56 mgrms. per litre. Lehmann also investigated the amount of copper, as acetate, which could be dissolved in wine before the taste betrayed its presence: with 50 mgrms. per litre no copper taste; with 100 mgrms. there was a weak after taste; with 150 mgrms. it was scarcely drinkable, and there was a strong after taste; with 200 mgrms. per litre it was quite undrinkable, and the colour was changed to bluish-green. Vinegar, acting under the most favourable circumstances on sheet brass or copper, dissolved, in seven days, 195 mgrms. of copper per litre from the copper sheet, 195 from the brass sheet.
Lehmann discusses the amount of copper which may be taken at a meal under the circumstance that everything eaten or drank has been artificially coppered, but none “coppered” to the extent by which the presence of the metal could be betrayed by the taste; and the following is, he thinks, possible:—
| 300 c.c. of soup boiled in a copper vessel, | 20 | mgrms. Cu. |
| 1 litre of wine which has been standing in a copper vessel, | 50 | „ |
| 50 c.c. vinegar which has been kept in a copper vessel, | 10 | „ |
| 50 grms. of fat which has been used for frying in a copper vessel, | 5 | „ |
| 200 grms. of strongly coppered peas, | 50 | „ |
| 500 grms. of strongly coppered bread, | 60 | „ |
The total only amounts to 195 mgrms. of copper, which only slightly exceeds a high medicinal dose. The metal is tasted more easily in liquids, such as wine, than in bread; bread may be coppered so that at a meal a person might eat 200 mgrms. of a copper compound without tasting it.
It is pretty well accepted that cooking in clean bright copper vessels will not contaminate any ordinary food sufficiently to be injurious to health.