A manual of practical hygiene : prepared especially for use in the medical service of the Army / by Edmund A. Parkes.

Date:
1864
Catalogue details

Licence: Public Domain Mark

Credit: A manual of practical hygiene : prepared especially for use in the medical service of the Army / by Edmund A. Parkes. 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.

    64/686 (page 34)
    Usually this process gives good results. Occasionally, from some cause of which I am ignorant, the sulphate of baryta does not precipitate. This does not depend on the amount of sulphuric acid. The ease with which this pro- cess is done renders it useful. Iron.—Evaporate one-half of the water to dryness; incinerate to destroy organic matter; if iron be present, the ash will be red. Dissolve in a smaU quantity of sulphuric acidj add zinc to reduce the iron to protoxide; dilute to 100 C.C. or any convenient quantity, and warm to 140° Fahr. Put the solution of permanganate of potash,* graduated for the organic matter, into a burette, and add it to the water till the faintest red tint is permanent. Cal- culate how much would be used for the litre, and deduct 0-24 C.C. Multiply remainder by co-efficient of iron, or oxide or carbonate of iron. Grammes. 1 C.C. of permanganate, = '00172 iron. ,, „ = •002211 protoxide of iron. ,, ,, = 003562 carbonate of iron. If, in a water containing iron, the amount of organic matter and iron has been previously determined, the amoimt of permanganate used for the iron must be now deducted from the total amount to obtain the exact quantity of permanganate decomposed by organic matter alone. Silica and Iron.—Take the dried solids; add strong hydrochloric acid; evaporate to dryness; dissolve everything that will come away by repeated washing with hot water. Weigh remainder as silica and iron mixed. The amounts of the Nitric and Phosphoric Acids had better not be deter- mined by weight. If it is wished to do so, refer to Fresenius' Quantitative Chemical Analysis. Free Carbonic Acid.—Determination by the Soap Test.—In order to get rid of the fallacy from free carbonic acid acting on the soap, Clark recommended that the water should be well shaken in a bottle, so as to disengage some of the COj, and then that the air shoiild be sucked out. But this does not entirely remove the carbonic acid. By the soap test the free carbonic acid can be determined in the following way : Throw down all the lime carefully, without adding an excess of oxalate of ammonia, and determine the hardness in 50 C. C. as usual. The hardness will be owing to magnesian salts, iron, if it exists (or alumina or barj'ta in mineral waters), and carbonic acid. If, now, the water be boiled, and the loss of water replaced by distilled water, the carbonic acid will be driven off, and the hardness again determined. The difference between the first and second trials will (if no iron exist in the water), give the amount of soap solutions which had been previously acted on by the carbonic acid. Example.—1. Total magnesian and carbonic acid hardiness, = 12° 2. -Magnesian hardness, . . . . = 7° Carbonic acid hardness, . . = 5° * This solution of permanganate is merely used because it lias been already graduated for the organic matter. Otherwise it is more convenient to use a decinorinal solution of the per- manganate, or to use the bichromate of potash, which, in some respects, is superior to the pennanganate ; as 1 atom of bichromate gives up 3 atoms of oxygen, the decinonnal solution is 1 th of an equivalent (=4-919 grammes) dissolved in 1000 C.C. ; 1 C.C. is equal to TtiitTrirtll atom of a protosalt, or i^f^^th of a persalt (75^77*'^ ^t' i^ = 'OOOTS). The end of the reaction is known by bringing a drop of the mixture in contact with a drop of freshly prepared red pnissiate of potash on a white slab (Sutton, p. 94). The colour at the point of contact is blue as long as protoxide of iron exists, then is ^en, and then brownish ; the disappearance ol the greenish-bluc tint indicates the point at which all the iron is oxidized.