56 



METHODS OF ANALYSIS 



[Chap. 



17 



RAW AND SPENT MATERIALS. 



(Under raw materials are included woods, barks, leaves, etc.) 

 MOISTITRE IN SAMPLE AS RECEIVED. 



Cut or break up large pieces and mix the sample rapidly to avoid change in mois- 

 ture content. Dry as directed under 2, a suitable weighed quantity, dependent upon 

 the physical condition and moisture content of the sample. 



18 PREPARATION OF SAMPLE. 



Dry the remainder of the sample at a temperature not above 60°C. and grind to 

 pass through a 20 mesh sieve. 



19 MOISTURE IN PREPARED SAMPLE. 



Take 10 grams of the sample prepared in 1 8, dry as directed under 2, and calculate 

 all results to an "as received", "air dry", or "moisture free" basis as desired. 



20 EXTRACTION. 



FIG. 4. METAL EXTRACTOR USED FOR EXTRACTING TANNING MATERIALS. 

 (For spent materials approximate the follov/ing quantities as closely as possible.) 



Place a quantity of the dried sample, containing 3.75-4.25 grams of tannin, in a 

 beaker and wet thoroughly with hot water. Place a perforated porcelain plate in 

 a tin-lined copper extractor of the general form shown in Fig. 4, and on the plate 

 place a layer of cotton and wet thoroughly with water. Connect the extractor with 

 an 800 cc. Erlenmeyer flask (G), open the stock-cock (E) and close the outlets (C) 

 and (D). Pour into the extractor the material to be extracted, washing it into the 

 extractor with hot water. Return the percolate through the extractor until it is 

 practically clear. Place a layer of cotton on top of the material. Close the stop- 

 cock (E), connect with an 800 cc. Erlenmeyer flask containing about 650 cc. of water, 

 connect (D) by a delivery tube wuth a liter graduated collecting flask, return the 

 total percolate to the extractor and connect by means of the metal cap (B) with a 

 block tin condenser (A) in such a way that the condensate will drip upon the layer 

 of cotton. Boil the water in the flask, and collect 400-500 cc. of percolate from the 

 side tube (D). Open the stop-cock (E) and close the side tube (D), add water to the 

 flask (G), if necessary, until it contains about 200 cc. Continue the extraction with 

 water at steam heat, allowing the percolate to run back into the boiling flask. Re- 



