FOODS AND FEEDING STUFFS. 



53 



solution of ferric sulphate in 20 per cent sulphuric acid, receiving the rinsings 

 in the beaker containing the precipitate. After the cuprous oxid is dissolved, 

 wash the solution into a large Erlenmeyer flask and immediately titrate with a 

 standard solution of potassium permanganate. One cc of the permanganate 

 solution should equal 0.010 gram of copper. In order to determine the strength 

 of this solution, make six or more determinations with the same sugar solution, 

 titrating one-half of the precipitate obtained, and determining the copper in the 

 others by electrolysis. The average weight of copper obtained by electrolysis, 

 divided by the average number of cubic centimeters of permanganate solution 

 required for the titration, is equal to the weight of copper equivalent to 1 cc of 

 the standard permanganate solution. A solution standardized with iron or 

 oxalic acid will give too low results. 



(6) DIRECT WEIGHING OF CUPROUS OXID. 



Prepare a gooch with an asbestos felt one-fourth of an inch thick. First 

 thoroughly wash the asbestos with water to remove small particles, then follow 

 successively with 10 cc of alcohol and 10 cc of ether, and dry the crucible and con- 

 tents thirty minutes in a water oven at the temperature of boiling water. 



Collect the precipitated cuprous oxid on the felt as usual, thoroughly wash 

 with hot water, then with 10 cc of alcohol, and finally with 10 cc of ether. Dry 

 the precipitate thirty minutes in a water oven at the temperature of boiling 

 water ; cool and weigh. The weight of cuprous oxid multiplied by 0.8883 gives 

 the weight of metallic copper. 



8. Starch. 



(a) DIRECT ACID HYDROLYSIS (MODIFIED SACHSSE METHOD a). OFFICIAL. 



Stir a convenient quantity of the sample (representing from 2.5 to 3 grams 

 of the dry material) in a beaker with 50 cc of water for an hour. Transfer to 

 a filter and wash with 250 cc of water. Heat the insoluble residue for two and 

 a half hours with 200 cc of water and 20 cc of hydrochloric acid (specific gravity 

 1.125) in a flask provided with a reflux condenser. Cool, and nearly neutralize 

 with sodium hydroxid. Complete the volume to 250 cc, filter, and determine the 

 dextrose in an aliquot of the filtrate as directed in (b) (2), page 49. The 

 weight of the dextrose obtained multiplied by 0.90 gives the weight of starch. 



(b) DIASTASE METHOD WITH SUBSEQUENT ACID HYDROLYSIS. PROVISIONAL. 



(1) PREPARATION OF MALT EXTRACT. 



Digest 10 grams of fresh, finely ground malt two or three hours at ordinary 

 temperature with 200 cc of water and filter. Determine the amount of dextrose 

 in a given quantity of the filtrate after boiling with acid, etc., as in the starch 

 determination, and make the proper correction in the subsequent determination. 



(2) DETERMINATION. 



Extract a convenient quantity of the substance (ground to an impalpable 

 powder and representing from 4 to 5 grams of the dry material) on a hardened 

 filter with five successive portions of 10 cc of ether; wash with 150 cc of 10 



a In this method there will be included as starch the pentosans and other carbohydrate 

 bodies present which suffer hydrolysis and conversion into reducing sugars on boiling 

 with hydrochloric acid. 



