Public health laboratory work / by W. Watson Cheyne, W.H. Corfield and Charles E. Cassal.

  • Cheyne, William Watson, Sir, 1852-1932.
Date:
1884
Catalogue details

Licence: Public Domain Mark

Credit: Public health laboratory work / by W. Watson Cheyne, W.H. Corfield and Charles E. Cassal. Source: Wellcome Collection.

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    of milk weighed out in a platinum capsule, and by burning this residue the percentage of ash (mineral matter) is arrived at. The amount of solids yielded by pure milk varies from 11*5 to 14 per cent ; when the percentage falls below 11, the milk is very poor, and has probably been sophisticated. The fat is obtained by extracting about 10 grammes of the milk, previously evaporated to a semi solid consistence, by means of ether; the solution of the fat in the ether, passed through a filter and collected in a weighed vessel, is evaporated in the latter until the whole of the volatile solvent has disappeared, and the weight of fat thus obtained. After the extraction of fat there remain caseine, milk- sugar and mineral matter. By treatment with alcohol and water the milk-sugar, and part of the ash are removed ; the residue consists of caseine and a little phosphate of lime, which may be dried and weighed, burnt, and the ash weighed ; the latter, deducted from the first weight, gives the quantity of caseine. The milk-sugar may be determined in the weak alcoholic extract above mentioned, by means of Fehling's copper solution, as previously described under Sugar ; or a given weight of milk may be coagulated with acetic acid, and the clear whey may be taken for the determination of sugar. The solids not fat that is, the caseine, salts, and lactin, obtained by direct experiment or by deducting the percentage of fat from the percentage of total solid matter, is a fairly constant quantity, i.e.^ is not =? subject to the variation of the single constituents. IThis percentage is taken at 9*3, and knowing that 100 parts by weight of pure milk will yield 9*3 of solids not fat, it is of course possible to calculate how much pure milk there is in any particular sample. The percentage of cream thrown up by milk in a given time, is determined by an instrument called a creamoineter. This is a long tube in which the milk cREAMo- allowed to stand and which is graduated to give METER, percentages. Many ingenious adulterations of milkhave been devisedand [H. 17.] G