Chemistry, inorganic and organic : with experiments and a comparison of equivalent and molecular formulæ / by Charles Loudon Bloxam.
- Charles Bloxam
- Date:
- 1867
Licence: Public Domain Mark
Credit: Chemistry, inorganic and organic : with experiments and a comparison of equivalent and molecular formulæ / by Charles Loudon Bloxam. Source: Wellcome Collection.
72/748 page 44
![tion of the free carbouic acid contained in the water by the addition of a certain quantity of lime; the lime thus added combines with the free carbonic acid, and the carbonate of lime so produced separates together with the carbonates of lime and magnesia, which were previously retained in solution by the free carbonic acid; this process, therefore, affects chiefly the temporary hardness; moreover, the earthy carbonates which are sepa- rated appear to remove from the Avater a portion of the vegetable matter which it contains, and thus effect a very important ijurification. The water under treatment is mixed in large tanks, with a due proportion of lime previously diffused tlirough water (the quantity necessary having been determined by preliminary experiment), and the mixture allowed to settle until perfectly clear, when it is drawn off into reservoirs.* Waters which axe turbid from the presence of clay in a state of sus- pension, are sometimes purified by the addition of a small quantity of alum or sulphate of alumina, when the alumina is precipitated by the car- bonate of lime, and carries down with it mechanically the suspended clay, leaving the water clear. The organic matter contained in waters may be vegetable matter dis- solved from the earth, with which it has come in contact, or resulting from the decomposition of plants, or it may be animal matter derived either from the animalcules and hsh naturally existing in it, or from the seAvage of towns, and, in the case of Avell waters, from surface drainage. It is a pretty generally received opinion that such of these organic matters as are very susceptible of chemical change have an injurious effect upon the system of persons drinking the water, and it is now usual, in ex- amining water as to its fitness for consimiption, to ascertain how much of the organic matter is in a changeable condition, by determining with the aid of a solution of permanganate of ]Dotasli the amount of oxygen neces- sary to effect its conversion into more stable forms. 41. One of the most important points to be taken into account in estimating the qualities of a water is its action upon lead, since this metal is unfortunately so generally employed for the storage and transmission of water, and cases frequently occur in which the health has been seriously injured by repeated small doses of compoimds of lead taken in water, Avhich has been kept in a leaden cistern. If a piece of bright, freshly scraped lead be exposed to the air, it speedily becomes tarnished from the formation of a thin film of the oxide of lead, produced by the action of the atmospheric oxygen; this oxide of lead is soluble in water to some extent, and hence, when lead is kept in contact with water, the oxygen Avhich is dissolved in it acts upon the metal, and the oxide so produced is dissolved by the Avater; but, fortunately, different Avaters act Avith A^ery different degrees of rapidity upon the metal, according to the nature of the substances which they contain. The film of oxide which forms iipon the surface of the lead is in- soluble, or nearly so, in Avater containing much sulphate or carbonate of lime, so that hard waters may generally be kept Avithout danger in leaden cisterns • but soft waters, and those Avhich contain nitrites or nitrates, should not be drunJc after contact Avith lead. Nearly all Abaters Avhich have been stored in leaden cisterns contain a trace of the metal, and since the action of this poison, in minute doses, upon the system is so gradual * riiaincs ami Now River water are softened, in this way, to 3°'5, or to a lower point tlian hy an liouv's lioilin.](https://iiif.wellcomecollection.org/image/b21496602_0072.jp2/full/800%2C/0/default.jpg)
