Food : its adulterations, and the methods for their detecton / by Arthur Hill Hassall.

Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: Food : its adulterations, and the methods for their detecton / by Arthur Hill Hassall. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    been found to be hurtful; illnesa has also resulted from the con- sumption of waters containing other metals, as iron, zinc, copper and arsenic, ACTIOir OF WATEE ON lEAD AND ZINC. A gi'eat deal has been said and written on the important subject of the action of water on the leaden pipes through which it is conducted to the consumer, and on the cisterns in which it is stored. Although the statements made are somewhat contradictory, yet the actual facts may now be said to be well ascertained and established. For many years it was universally believed that soft waters acted most on lead and hard least, but, as will be presently shown, this statement is not corroborated by further and more exact observa- tions and experiments, the action of soft waters on lead being due not to the water itself, but to the oxygen and other substances with which it is more or less impregnated. First. The gases and salts which most attack lead are oxygen, nitrous and nitiic acids, whether free or combined •, all the chlorides ; caustic lime, as contained in mortar, &c., soluble compounds being formed with all these. Carbonic acid likewise attacks lead, but the resulting compound is in- soluble unless in the presence of a considerable excess of carbonic acid. Thus a film or coating is frequently foimd on the sm-face of lead cisterns and pipes, consisting usually of a basic carbonate of lead, with two molecules of carbonate of lead and one molecule of hydrated oxide. But according to Mr. Lauder Lindsay, this coating has frequently a more complex composition, and consists of the carbonates, phosphates, and sulphates of lime and magnesia, with some chloride of lead. This film or cmst is liable to become difiiised through the water when it is agitated, and in this way it may be introduced into the system ; but it is said that the coating thus formed on the surface of lead exerts a protective effect by retarding or preventing the action of the other substances on the metal. According to Medlock, nitrite of ammmiia exerts the greatest influence on lead, the nitrite of that metal being formed. The nitrite of ammonimn being a volatile salt, is found in most distilled waters obtained from an impure soiu-ce. The salts which exert the least action on lead are carbonate, sulphate, and, according to Franldand, especially phosphate of lime; also in a less degree the corresponding salts of magnesia and the alkaline phosphates. Second. Organic substances affect lead powei-fully, and the organic acids generally, as those derived from fruit, beer, milk, cider, &c. Third. Another way in which lead becomes dissolved is by gal- vanic action, as when lead comes into contact with iron, zinc, or tin. Zinc pipes often contain considerable quantities of lead, and hence,