A manual of practical hygiene for students, physicians, and health officers / By Charles Harrington.

  • Harrington, Charles, 1856-1908.
Date:
1914
Catalogue details

Licence: Public Domain Mark

Credit: A manual of practical hygiene for students, physicians, and health officers / By Charles Harrington. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

    172/992 (page 162)
    which depends upon the conversion of the nitrogenous matter into ammonium sulphate, which then is decomposed by an excess of strong alkaU, ammonia being set free. This is expelled by heat, condensed with the accompanying steam, and received in acid of known strength. The process is as follows : Into a Kjeldahl digestive flask introduce a definite weight, say 5 grams of milk, about 0.7 gram of mercuric oxide, and 20 cc. of sulphuric acid of 1.840 specific gravity, free from nitrates and ammonium sulphate. Place the flask in an inclined posi- tion and heat below the boiling-point of the acid for from five to fifteen minutes, or until frothing ceases. Then raise the heat until the mixture comes to boiling, and continue the process until the liquid is clear and has a very pale straw color. This will require ordinarily less than an hour. Withdraw the lamp, and drop in, in small quantities at a time, permanganate of potassium, until, after shaking, the liquid acquires a permanent green or purple color. This addition is not always or even usually necessary to secure complete oxidation, but since it is sometimes required, it is best to make it a part of the routine. Allow the contents to cool, and then transfer them with about 200 cc. of distilled water, plus sufficient for thorough rinsing, to a distilhng flask of about 550 cc. capacity, fltted with a rubber stopper and a bulb tube connected with a very long Liebig condenser, the delivery end of which is fitted with a glass tube bent at right angles, so that it may dip beneath the surface of the acid into which the distillate is to be received. Add a few pieces of pumice or granulated zinc, or about 0.5 gram of zinc dust, to pre- vent bumping, and 25 cc. of a 4 per cent, aqueous solution of sulphide of potassium, to prevent the formation of compounds of ammonium and mercury, which are not wholly decomposable by alkalies. Shake, and then add of a saturated solution of sodium hydrate, free from nitrates, sufficient to make the reaction strongly allialine, pouring it down the side of the flask so as not to mix at once with the acid con- tents. Next connect the flask with the condenser, mix the contents by gently rotating, and apply the flame. Distil, and receive the distillate m a vessel containing 50 cc. of decinormal sulphuric acid. When about 175 cc. have passed over, it may be assumed that all ammonia has been expelled, and then the distillate is titrated with decinormal alkali, using cochineal or methyl-orange as an indicator. Fi'om the difference in strength of the decinormal acid, the amount of ammonia is calculated, and from this the amount of nitrogen ; and this multijilied by 6.38 gives the total proteins. Detection of Added Water.—One of the most difficult problems which comes to the food and drug analyst is that of determining whether a sample of low standard milk is such because it comes from a variety of cows normally giving such low standard milk or whether the deficiency in quality is due to the addition of water. Methods for the detection of added water in milk depend upon being able to show abnormal chemical or physical constants which can be explained only by the addition of water, there being no test which will distinguish between the water which may be added to the milk and the