V. TANNING MATERIALS.— TENTATIVE. 

 EXTRACTS. 



1 PREPARATION OF SOLUTION. 



(a) Solid extracts. — Grind solid extracts in a large porcelain mortar, so that the 

 material will pass through a 10 mesh sieve, mix thoroughly and weigh out a quantity 

 containing 3.75-4.25 grams of tannin. This shouldbedone as rapidly as possible to 

 avoid change in moisture content. Pour into 100 cc. of water at 85''C., place on a 

 steam bath and stir until a homogeneous solution is obtained. Transfer to a 1 liter 

 flask with 800 cc. of water at 85°C. Cool rapidly to 20°C. and make up to 1 liter. 



(b) Fluid extracts. — Allow fluid extracts to come to room temperature and mix 

 thoroughly. Weigh out rapidly a quantity containing 3.75-4.25 grams of tannin. 

 Dissolve by washing into a 1 liter flask with 900 cc. of water at 85°C. Cool rapidly 

 to 20°C. and make up to 1 liter at 20°C. 



After the preparation of the solutions, proceed at once with the analj'sis. 



2 TOTAL SOLIDS. 



Thoroughly' mix the prepared solution, pipette at once 100 cc. into a tared flat- 

 bottomed glass dish, 2|-3 inches in diameter, and (1) evaporate and dry for 16 hours 

 in a combined evaporator and dryer' at 98°-100°C. ; or, (2) after evaporating on the 

 steam bath, dry for 12 hours on the bottom of a water oven at 98°-100°C. Remove 

 immediately to desiccators containing sulphuric acid (place no more than 2 dishes in 

 1 desiccator) and weigh rapidlj' when cooled. Calculate the percentage of total 

 solids. 



SOLUBLE SOLIDS. 



3 PREPARATION OF FILTER. 



The kaolin used should be neutral to phenolphthalein and should not yield more 

 than 1 mg. of soluble solids per 100 cc. of filtrate of a 1% suspension after an hour's 

 digestion at 20°C. Dry on a water bath and preserve in a tightly stoppered bottle. 

 Add about 75 cc. of the solution, as prepared under 1 , to 1 gram of the kaolin in a 

 beaker. Stir and pour immediately into a single, 15 cm. No. 590, S. & S. folded 

 filter. Return the filtrate to the paper when approximately 25 cc. have run through, 

 repeat the operation for an hour, thus transferring all the kaolin to the paper. At 

 the end of an hour, discard the solution on the filter by siphoning it off, disturbing 

 the kaolin as little as possible. 



4 DETERMINATION. 



Bring about 150 cc. of the original solution, as prepared under 1 , to exactly 20°C. 

 Fill the filter, prepared as under 3, with this solution and discard the filtrate until 

 it runs through clear. Keep the filter full, the temperature of the filtering solution 

 at 20°-25°C., and the funnel and receiving vessel covered. Pipette at once 100 cc. of 

 the clear filtrate into a tared dish, evaporate and dry as directed under 2. Calculate 

 the percentage of soluble solids. 



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