36 METHODS OF ANALYSIS. 



bottles. Dissolve in 900 cc of water at 80 C. such a quantity of the extract 

 as will give from 0.35 to 0.45 gram of tannin in 100 cc of solution. Allow to 

 cool slowly for from 12 to 20 hours at a temperature not below 20 C. and dilute 

 to 1 liter. 



(b) TOTAL SOLIDS. 



Thoroughly mix the solution, immediately pipette 100 cc into a tared dish, 

 evaporate, and dry as directed under " 4. Evaporation and drying." 



(c) SOLUBLE SOLIDS. 



Add 75 cc of solution (kept at from 20 to 25 C. during filtration) to 2 

 grams of kaolin (free from soluble salts), stir, let stand 15 minutes, decant, 

 and discard as much as possible of the supernatant liquid, and again add 75 cc 

 of the tannin solution to the kaolin. Stir, and pour immediately on a 15 cm, 

 No. 590 folded filter. Keep the filter full and the funnel and receiving vessel 

 covered. Reject the first 150 cc of filtrate, evaporate and dry the next 100 cc 

 (which must be as clear as practicable), as directed under "4. Evaporation 

 and drying." 



(d) NONTANNINS. 



Prepare a sufficient quantity of hide powder in the following manner: 

 Digest with 25 times its weight of water until thoroughly soaked; add 3 per 

 cent of chrome alum in solution, agitate occasionally for several hours, and 

 allow to stand over night. Wash, by squeezing through linen, until the wash 

 water gives no precipitate with barium chlorid. Squeeze the hide, using a 

 press if necessary, so that it contains from 70 to 75 per cent of water, and 

 determine moisture (20 grams is a convenient quantity). 



Add to 200 cc of the tannin solution such a quantity of the wet hide as con- 

 tains from 12 to 13 grams of dry hide, shake for 10 minutes in a shaker and 

 squeeze immediately through linen. Add 2 grams of kaolin to the filtrate, stir, 

 and filter through a folded 20 cm filter (No. 1 F Swedish recommended), 

 returning until clear. Evaporate and dry 100 cc as directed under " 4. Evap- 

 oration and drying." Correct the weight of the residue for dilution caused by 

 the water contained in the wet hide powder. 



The nontannin filtrate must not give a precipitate with a gelatin-salt solution 

 (1 per cent of gelatin and 10 per cent of salt). 



(e) TANNIN. 



The difference between the weight of the soluble solids and the corrected 

 nontannin residue is the weight of tannin in 100 cc of solution. 



3. Liquors. 



(a) PREPARATION OF SOLUTION. 

 Dilute to contain approximately 0.7 gram of solids in 100 cc of solution. 



(b) TOTAL SOLIDS. 

 Proceed as in extracts, 2 (b). 



(c) SOLUBLE SOLIDS. 

 Proceed as in extracts, 2 (c). 



