VI. GENERAL METHODS FOR THE ANALYSIS OF FOODS AND 

 FEEDING STUFFS. 



1. Moisture. Official. 



Dry a convenient quantity of the substance, representing about 2 grams of 

 dry material, at the temperature of boiling water until it ceases to lose weight 

 (approximately five hours), in a current of dry hydrogen or in vacuo. If the 

 substance be held in a glass vessel the latter should not be in contact with the 

 boiling water. 



2. Ash. Official. 



Char a convenient quantity of the substance, representing about 2 grams of 

 the dry material, and burn until free of carbon at the lowest possible heat. If 

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

 with 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 the whole to a low redness and weigh. 



3. Crude Protein. Official. 



Determine nitrogen as directed under fertilizers "4. (a) or (b)," page 5, and 

 multiply the results by 6.25. 



4. Albuminoid Nitrogen. Official, 

 (a) PREPARATION OF STUTZER'S REAGENT. 



Prepare cupric hydroxid as follows: Dissolve 100 grams of pure copper sul- 

 phate in 5 liters of water, add 2.5 cc of glycerol, and then a dilute solution 

 of sodium hydroxid until the liquid is just alkaline; filter, rub the precipitate 

 up with water containing 5 cc of glycerol per liter, and wash by decantation or 

 filtration until the washings are no longer alkaline. Rub the precipitate up 

 again in a mortar with water containing 10 per cent of glycerol, thus preparing 

 a uniform gelatinous mass that can be measured with a pipette. Determine the 

 quantity of copper hydroxid per cubic centimeter of this mixture. 



(b) DETERMINATION. 



Place 0.7 gram of the substance in a beaker, add 100 cc of water, and heat to 

 boiling, or, in case of substances rich in starch, heat on the water bath ten 

 minutes ; add a quantity of copper hydroxid mixture containing about 0.5 gram 

 of the hydroxid ; stir thoroughly, filter when cold, wash with cold water, and, 

 without removing the precipitate from the filter, determine nitrogen according to 

 one of the methods given for the determination of nitrogen in fertilizers (4. (a) 

 or (b), p. 5), adding sufficient potassium sulphid solution to completely 

 precipitate all copper and mercury. The filter papers used must be practically 



