54 METHODS OF ANALYSIS [Chap. 



5 INSOLUBLE SOLIDS. 



The difference between the percentage of the total solids and the percentage of 

 soluble solids is the percentage of the substance insoluble in water at 20''-25°C. 



NONTANNINS. 



6 REAGENTS. 



Hide powder. — This should be of woolly texture, well delimcd, and 10 grams of the 

 water-free powder should require 12-13 cc. of N/10 sodium hydroxid to neutralize it. 



Calculate the amount of air-dry hide powder which will be required for the number 

 of determinations to be made, on a basis of 13 grams of air-dry hide powder for 

 each determination. Increase this calculated amount by 35 grams of dry hide 

 powder to provide a sufficient amount for all the determinations. 



Thoroughly digest the total amount of hide powder with 10 times its weight of 

 water. Then for each gram of the hide powder, so digested, add 1 cc. of 3% chrome 

 alum solution; and either agitate frequently for several hours and let stand overnight 

 or agitate in some form of mechanical shaker for an hour. Transfer to a strong 

 linen filter and squeeze thoroughly. Remove from the filter and digest for 15 minutes 

 with a quantity of water equivalent to 15 times the weight of the dry hide powder 

 employed. Filter and squeeze to approximately 73% of water, using a press if 

 necessary. Very strong pressure is required to reduce the water content below 

 70%. Repeat the digestion and filtration 3 times. Determine moisture in 20 grams 

 of the squeezed hide powder as directed under 2. 



7 DETERMINATION. 



Place 46 grams of the wet hide powder in a suitable container of about 300 cc. 

 capacity, add 200 cc. of the tanning solution, as prepared under 1, and shake for 10 

 minutes in a mechanical shaker. Squeeze immediately through linen, add 2 grams 

 of kaolin, as used under 3, to the filtrate which contains the nontannins, stir, and 

 filter through a single, folded 18.5 cm. filter paper (No. IF. Swedish, preferred), 

 refiltering until the filtrate is clear. The filtrate should give no precipitate with a 

 gelatin-salt solution (1% gelatin and 10% salt). Pipette 100 cc. of the filtrate into 

 a tared dish and evaporate as directed under 2. Correct the weight of the nontannin 

 residue for the dilution caused by the water retained in the wet hide powder. Cal- 

 culate the percentage of nontannins. 



8 TANNIN. 



The difference between the percentage of the solu})le solids and the percentage 

 of nontannins is the percentage of tannin. 



DETECTION OF SULPHITE-CELLULOSE. 



9 REAGENTS. 



Siilphile-celtulose solution. — Dissolve 0.5 gram of the total solids, derived from 

 sulphite-cellulose, in 1 liter of water.and add sufficient tanning material, free from 

 sulphite-cellulose, to give a concentration of 3.75-4.25 grams of tannin per liter. 



10 DETERMINATION. 



Place 5 cc. of the tanning solution, prepared as under 1 , in a test tube; add 0.5 cc. 

 of anilin and shake well; then add 2 cc. of concentrated hydrochloric acid and mix 

 again. Compare the precipitate formed with that produced when the above sul- 



