VIII. FOODS AND FEEDING STUFFS. 



1 PREPARATION OF SAMPLE.— OFFICIAL. 



Grind the sample so that it will pass through a sieve having circular openings 

 it inch (1 mm.) in diameter. If the sample can not be ground, reduce it to as fine a 

 state as possible. 



2 Direct Drying. — Official. 



Dry a quantity of the substance, representing about 2 grams of dry material, 

 in a current of dry hydrogen or in vacuo at the temperature of boiling water to 

 constant weight (approximately 5 hours). If the substance be held in a glass vessel, 

 the latter should not be in contact with the boiling water. 



3 Drying in Vacuo without Heat. — Tentative. 



Mix the sample thoroughly and weigh by difference 2-5 gram portions from a 

 stoppered weighing bottle into tared, covered crucibles. Where subsequent fat 

 determinations are to be made, fat extraction cones may be used. Substances that 

 dry down to horn-like material should be mixed with fat-free cotton or other suit- 

 able material (previously tared with the container). Place 200 cc. of fresh concen- 

 trated sulphuric acid in a strong, tight 6 inch vacuum desiccator. Put triplicate 

 samples in separate desiccators, and exhaust by means of a vacuum pump. If a 

 pump is not available, place 10 cc. of ether in a small beaker in the desiccator, and 

 exhaust with a water filter pump. 



Between the pump and the desiccator interpose an empty bottle, next to the 

 desiccator, and a bottle of water. Draw the air from the desiccator through the 

 water and turn the desiccator stop-cock at just the instant when the water begins 

 to rise in the tube leading from the empty bottle. 



Gently rotate the desiccator 4 or 5 times during the first 12 hours to mix the sul- 

 phuric acid with the water which has collected as an upper layer. At the end of 24 

 hours open the desiccator, forcing the incoming air to bubble through concentrated 

 sulphuric acid, and make the first weighing. After weighing place in a desiccator 

 containing fresh concentrated sulphuric acid and exhaust as before. Rotate the 

 desiccator several times during the interval and weigh again after a suitable period 

 of drying. Repeat this process of drying in vacuo over sulphuric acid until the 

 weight is constant. 



4 ASH.— OFFICIAL. 



Char a quantity of the substance, representing about 2 grams of the dry material, 

 and burn until free from carbon at a low heat, not to exceed dull redness. If a 

 carbon-free ash can not be obtained in this manner, exhaust the charred mass with 

 hot water, collect the insoluble residue on a filter, burn till the ash is white or nearly 

 so, and then add the filtrate to the ash and evaporate to dryness. Heat to low 

 redness till the ash is white or grayish white and weigh. 



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