FOODS AND FEEDING STUFFS. W 



free from nitrogen. If the samples consist of material rich in alkaline phos- 

 phates (such as seeds, seed residue, and oil cake), add from 1 to 2 cc of a con- 

 centrated solution of potassium or sodium alum, free from ammonia, Just before 

 adding the copper hydroxid, and mix well by stirring. This serves to decom- 

 pose the alkaline phosphates. If this be not done copper phosphate and free 

 alkali may be formed, and the protein-copper precipitate may be partially 

 dissolved in the alkaline liquid. 



5. Crude Fat or Ether Extract. Official, 

 (a) PREPARATION OF ANHYDROUS ETHER. 



Wash any of the commercial brands of ether with two or three successive 

 portions of distilled 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 carefully cleaned metallic sodium cut into small pieces, 

 and let stand until there is no further evolution of hydrogen gas. The ether 

 thus dehydrated must be kept over metallic sodium, and should be lightly stop- 

 pered in order to allow any accumulating hydrogen gas to escape. It may be 

 drawn off with a pipette as required. 



(b) DETERMINATION. 



(1) DIRECT METHOD. 



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

 of the dry material, dried as for the determination of moisture, with anhydrous 

 alcohol-free ether for sixteen hours. Dry the extract at the temperature of 

 boiling water for one-half hour, remove from the oven to a desiccator, cool and 

 weigh ; continue this alternate drying and weighing at half-hour intervals until 

 a minimum weight of fat is obtained. For most feeds a period of from one to 

 one and one-half hours is required to obtain a minimum weight. 



(2) INDIRECT METHOD. 



Determine moisture as above, extract the dried substance for sixteen hours 

 as directed under the direct method, dry again and regard the loss of weight 

 as ether extract. 



6. Sucrose. 



OPTICAL METHODS, 

 (a) GENERAL DIRECTIONS FOR RAW SUGARS. PROVISIONAL. 



1. In general, make all sugar tests at 20 C. 



2. Graduate the saccharimeter at 20 C. Dissolve 26.000 grams of pure 

 sugar in water, and make the volume up to 100 metric cc (or 26.048 grams of 

 pure sugar in 100 Mohr cc), all weighings to be made in air with brass weights. 

 Complete the volume and make the polarization at 20 C. on an instrument 

 graduated at 20 C. This should give an indication of 100 on the scale of the 

 saccharimeter. For laboratories in which temperatures are usually higher 

 than 20 C., it is permissible to graduate saccharimeters at any suitable tem- 

 perature under the conditions specified above, providing that the analysis of 

 the sugar be made at the same temperature that is, that the volume be com- 

 pleted and the polarizations made at the temperature specified. 



International commission for unif3'ing methods of sugar analysis, Zts. Riib.-Zuck. 

 Ind., 1900, 37: 357. 



