The laboratory book of dairy analysis / by H. Droop Richmond.

Date:
1905
Catalogue details

Licence: In copyright

Credit: The laboratory book of dairy analysis / by H. Droop Richmond. 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.

    49/114 (page 35)
    tared filter paper ; remove the precipitate completely from the beaker by means of a policeman, and wash well (Fig. 23). Dry in the water oven, and extract the fat with ether, preferably in a Soxhlet extractor, and dry again till the weight is constant. Ignite the precipitate in the Gooch crucible, or place the filter containing the precipitate in a weighed basin and ignite it (if tared filters are used the tare should also be ignited in a weighed basin); subtract the weight of the ash (corrected if necessary for the ash of the tare) from the weight of the precipitate, and the difference will give the weight of the proteids. Estimation of Casein and Albumin.—Pipette loc.c. of milk into a beaker, add 90C.C. of water at 42°-43° 0. and 1.50.0. of a 10 per cent, solution of acetic acid ; stir well, and collect and weigh the precipitate as above. \_Notc.—This estimation or that given above may be combined with a fat estimation.] The precipitate is in this case casein. Raise the filtrate to boiling, and keep for 15 minutes on the water-bath; collect the precipitate as above, and weigh after drying; as fat and ash are absent the extraction and ignition may be omitted. The precipi- tate consists of albumin. Estimation of Nitrogen by Kjeldahl’s Method.—5c.c. of milk are pipetted into a long- necked hard glass flask; 2oc.c. pure sulphuric acid and a drop of mercury are added; a long stemmed bulb is placed in the neck; the flask is supported in an inclined position, and it is heated by a small flame ; at first water is driven off, next a consider- able amount of frothing takes place, and when this has subsided the flame may be turned up to such a height that the sulphuric acid distils up to and is con- densed in the neck ; 10 grammes of acid potassium sulphate may be added after the frothing has subsided, but this addition is hardly worth while with milk, as the operation is fast enough without it; the heating is continued till the licpiid in the flask is quite colourless.