V] TANNING MATERIALS 55 



phite-cellulose solution is similarly treated. Sulphite-cellulose is held to be present, 

 in the predetermined absence of the synthetic tanning material, Neradol-D, if the 

 precipitates are approximately equivalent in amount. 



LIQUORS. 



11 PREPARATION OF SOLUTION. 



Dilute the liquor with water at room temperature to contain approximately 0.7 

 gram of solids in 100 cc. of solution. If the liquor does not give a proper solution 

 with water at room temperature, it may be diluted with water at 80°C., and then 

 cooled rapidly to 20''C. 



12 TOTAL SOLIDS. 

 Proceed as directed under 2. 



13 SOLUBLE SOLIDS. 

 Proceed as directed under 4. 



14 NONTANNINS. 



Proceed as directed under 7, using the amount of wet chromed hide powder which 

 will give the ratio between the tannin and hide powder shown in the following table: 



TOTAL ACIDITY. 



1 5 REAGENTS. 



(a) Hematin solution.— Digest 0.5 gram of hematin in 100 cc. of cold neutral 95% 

 alcohol. 



(b) Gelatin solution. — Dissolve 10 grams of gelatin in hot water, cool, add 25 cc. of 

 95% alcohol and dilute. If the gelatin solution is acid or alkaline, neutralize with 

 N/10 sodium hydroxid or N/10 acetic acid, respectively, using hematin solution as 

 indicator and make up to 1 liter. 



(C) Kaolin. — Digest with dilute hydrochloric acid; wash and dry as under 3. 

 (d) N/IO sodium hydroxid. 



16 DETERMINATION. 



Add 25 cc. of the gelatin solution to 25 cc. of the tanning liquor in a stoppered 

 cylinder, dilute with water to 250 cc, add 15 grams of the kaolin and shake vigorously. 

 Allow to settle for at least 15 minutes, remove 30 cc. of the supernatant liquid, dilute 

 with 50 cc. of water and titrate with N/10 sodium hydroxid, using the hematin solu- 

 tion as indicator. Each cc. of N/10 sodium hj'droxid is equivalent to 0.2 % acid, 

 calculated as acetic, in the liquor. 



