DAIRY PRODUCTS. 



127 



cut take the sample with a cheese trier. If only one plug can be obtained take 

 it perpendicular to the surface of the cheese at a point one-third of the distance 

 from the edge to the center and extending either entirely or half way through 

 it When possible draw three plugs one from the center, one from a point 

 near the outer edge, and one from a point half way between the other two. 

 For inspection purposes reject the rind, but for investigations requiring the 

 absolute amount of fat in the cheese include the rind in the sample. It is 

 preferable to grind the plugs in a sausage machine, but when this is not done 

 they are cut very fine and carefully mixed. 



2. Moisture. Official. 



Place from 2 to 5 grams of cheese in a weighed platinum or porcelain dish 

 which contains a small quantity of porous material, such as ignited asbestos or 

 sand, to absorb the fat which may run out of the cheese. Heat in a water oven 

 for ten hours and weigh ; the loss in weight is considered as moisture. Or, if 

 preferred, the dish may be placed in a desiccator over concentrated sulphuric 

 p.cid and dried to constant weight. In some cases this may require as much as 

 two months. The acid should be renewed when the cheese has become nearly 

 dry. 



3. Ash. Official. 



The dry residue from the moisture determination may be used for the ash. 

 If the cheese be rich in fat, the asbestos will be saturated therewith. Ignite 



mtiously to avoid spurting, removing the lamp while the fat is burning off. 

 When the flame has died out, the burning may be completed in a muffle at low 

 redness. When desired, the salt may be determined in the ash in the manner 

 specified under butter analysis, page 124. 



4. Nitrogen. Official. 



Determine nitrogen by the Kjeldahl or Gunning method, as given on page 5, 

 under " I. Fertilizers," using about 2 grams of cheese, and multiply the per- 

 centage of nitrogen by 6.38 to obtain the nitrogen compounds. 



5. Fat. 



(a) GRAVIMETRIC METHOD. OFFICIAL. 



Cover the perforations in the bottom of the extraction tube with dry asbestos 

 felt, and on this place a mixture containing equal parts of anhydrous copper 

 sulphate and pure, dry sand to the depth of about 5 cm, packing loosely. Cover 

 the upper surface of this material with a film of asbestos. Place on this 2 to 

 5 grams of the sample and extract with anhydrous ether for five hours in a con- 

 tinuous extraction apparatus. Remove the cheese and grind it to a fine powder 

 with pure sand in a mortar, replace the mixed cheese and sand in the extraction 

 tube, washing the mortar with ether and adding the washings to the tube, and 

 continue the extraction for at least ten hours. 



(b) BABCOCK CENTRIFUGAL METHOD. PROVISIONAL. 



Weigh about 6 grams of cheese in a tared dish. Add 10 cc of boiling water 

 and stir with a rod until the cheese softens and an even emulsion is formed, 

 preferably adding a few drops of strong ammonium hydroxid, and keep th 

 beaker in hot water until the emulsion is nearly completed and the mass free 

 from lumps, 



