Introduction to the study of inorganic chemistry / by William Allen Miller.

  • Miller, William Allen, 1817-1870.
Date:
1871
Catalogue details

Licence: Public Domain Mark

Credit: Introduction to the study of inorganic chemistry / by William Allen Miller. Source: Wellcome Collection.

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    Hard and Soft J Fa tor. colour in sucii an experiment, there is no organic impurity to be feared in the water. U'ater is commonly spoken of as /nrrd or soft, according to its action upon soap. Soap is a combination of a fatty or oily acid with soda ; and this compound is readily soluble m pure water. Waters which contain salts of calcium or magnesium cause the soap to curdle, since these metals iurnish with the fatty acid of the soap compounds which are not soluble in water. Such waters are said to be /lard. Soap which is thus curdled is consumed in waiste. In such water soap neither cleanses nor iiroduces a lather until the w hole of the earthy salts have been decompo.sed and an e.\- cess of soap is present Soft w'aters, on the contrary, do not contain these earthy salt.s, and they dis.solve the soap without difficulty, and without destroying either its cleansing power or its tendency' to form a lather. ^lany waters e.xhibit what is called temporary hardness; such waters become softer by' boiling. I'he hardness in this case is due to the presence of calcic or magnesic carbonate. These com])ounds are scarcely soluble at all in pure water, but they become soluble to a considerable extent in water charged with uncombined carbonic acid. 'Wlien such waters are boiled, the carbonic acid is driven off by the heat, and the calcic and magnesic carbonates which the acid had dis- solved become deposited, and a ‘ fur’ or incrustation takes place on the inside of the boiler, as may be seen by^ examin- ing a kettle used for boiling such waters. 38. I lace half a litre of a water of the kind just referred to, such as that of the Thames or of the New River, in a glass flask, and boil it over a lamp for a quarter of an hour : little crystalline grains of the earthy carbonates which w'cre in solution will gradually be deposited, and the w'ater will be found to dl‘ considerably softened. ^■rp. 39. Mix another half litre of such a water before it is boiled with about one-eighth of its bulk of liinewater. The liquid will become turbid, and on standing for a few hours, till it IS clear, it will be found to be much softer than before.