V. METHODS FOR THE ANALYSIS OF TANNING MATERIALS. PRO- 



VISIONAL. 



1. Crude Materials, 

 (a) MOISTURE IN SAMPLE AS RECEIVED. 



Grind promptly and dry 10 grams as directed under "4. Evaporation and 

 drying." 



(b) PREPARATION FOR EXTRACTION. 



Dry the sample not above GO C. and grind to pass through a 20-mesh sieve. 

 (c) MOISTURE IN PREPARED SAMPLE. 



Dry 10 grams as directed under " 4. Evaporation and drying," and calculate 

 all subsequent determinations on the moisture-free basis. 



(d) EXTRACTION. 



Extract such a quantity of material as will give between 0.35 and 0.45 gram 

 of tannin per 100 cc of solution in an extractor which permits the removal of 

 the extract solution without allowing it to boil, using a layer of cotton to pre- 

 vent fine material from passing over. Collect from 400 to 500 cc in this way, 

 remove and continue extraction with a fresh portion of water at steam heat 

 in the usual way until the material is free of tannin, testing the last few cubic 

 centimeters of extract with gelatin-salt solution. 



For spent materials approximate the above proportions as closely as prac- 

 ticable. 



(e) ANALYSIS. 



Heat the extract to 80 C. and proceed as directed under extracts. In case 

 weaker solutions than the method specifies are employed the amount of hide 

 powder used must be reduced in proportion to the quantity of tannin present. 



2. Extracts, 

 (a) PREPARATION OF SOLUTION. 



Grind solid extracts rapidly, and thoroughly mix. Heat fluid extracts to 

 50 C., thoroughly mix, cool to room temperature, and weigh from weighing 



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