80 METHODS OF ANALYSIS [Chap. 



5 CRUDE PROTEIN.-OFFICIAL. 



Determine nitrogen as directed under I, 18,21, or 23, and multiply the result by 

 6.25. 



ALBUMINOID NITROGEN.— OFFICIAL. 



6 REAGENT. 



Stutzer's reagent.— Frepare cupric hydroxid as follows: Dissolve 100 grams of pure 

 copper sulphate in 5 liters of water, add 2.5 cc. of glycerol, and then dilute sodium 

 hydroxid solution 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% of glycerol, thus preparing a uniform gelatinous mass 

 that can be measured with a pipette. Determine the quantity of copper hydroxid 

 per cc. of this mixture. 



7 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 for 10 minutes ; 

 add a quantity of the Stutzer's reagent 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 the nitrogen according to I, 18, 21 or 23, 

 adding sufficient potassium sulphid solution to completely precipitate all of the 

 copper and mercury. The filter paper used must be practically free from nitrogen. 

 If the material (such as seeds, seed residue, or oil cake) is rich in alkaline phos- 

 phates, add, to decompose the alkaline phosphates, 1-2 cc. of a concentrated potash 

 or soda alum solution, free from ammonia, then the copper hydroxid, and mix well 

 by stirring. If this is not done, copper phosphate and free alkali may be formed, 

 and the protein-copper precipitate partially dissolved in the alkaline liquid. 



8 AMIDO NITROGEN.-OFFICDa. 



Subtract the amount of albuminoid nitrogen from the amount of total nitrogen 

 to obtain the amido nitrogen. 



CRUDE FAT OR ETHER EXTRACT. 



Direct Method. — Official. 



Anhydrous ether. — Wash any of the commercial brands of ether with 2 or 3 suc- 

 cessive portions of water, add solid sodium or potassium hydroxid, and let stand 

 until most of the water has been abstracted from the ether. Decant into a dry 

 bottle, add small pieces of carefully cleaned metallic sodium, and let stand until 

 there is no further evolution of hydrogen gas. Keep the ether, thus dehydrated, 

 over metallic sodium in lightly stoppered bottles. 



10 DETERMINATION. 



Large quantities of soluble carbohydrates may interfere with the complete ex- 

 traction of the fat. In such cases extract with water before proceeding with the 

 determination. Extract about 2 grams of material, dried as under 2 or 3, with the 

 anhydrous ether for 16 hours. Dry the extract at the temperature of boiling water 

 for 30 minutes, cool in a desiccator, and weigh; continue, at 30 minutes intervals, 

 this alternate drying and weighing to constant weight. For most feeds a period 

 of 1-1 i hours is required. 



