10 



Under 5 first line after "and " insert: " without filtering." 

 Omit all of and insert the following : 



6. DETERMINATION OF SOLUBLE SOLIDS. 



Filter about 125 cc of the solution through a double folded filter (S. and S. 

 No. 590, 15 cm) returning the filtrate through the filter once. Evaporate 100 cc 

 as before. 



Page 78, omit all of 7 and insert the following : 



7. DETERMINATION OF TANNING SUBSTANCES. 



Prepare 20 grams of hide powder by shaking for five minutes with 250 cc 

 of water and straining through linen. Repeat the operation three times. Finally, 

 remove as much water as possible by squeezing in a press. Transfer the pressed 

 hide powder to a covered dish, and weigh. Dry a portion approximately equal to 

 one-fourth of the whole to constant weight at 100. Add the remainder of the 

 hide powder to 200 cc of the original unfiltered solution and shake for ten min- 

 utes. Squeeze through linen, collect the filtrate, add 5 grams of kaolin free 

 from soluble salts, stir well, and filter through a folded filter (S. & S. No. 590, 

 15 cm), returning the first 25 cc. Evaporate 100 cc as before. The weight of 

 the residue must be corrected for the dilution caused by the water contained in 

 the hide powder. The shaking must be done in some form of mechanical shaker. 

 The simple machine used by druggists, and known as the "milk shake " is rec- 

 ommended. 



Page 78, at the end of VIII-1, insert: 



"Extracts must be heated to 50, well shaken, and allowed to cool slowly to 

 room temperature. " 



METHODS OF TANNIN ANALYSIS. 

 Add on page 78, after 7 : 



"8. TESTING THE NONTANNIN FILTRATE. 



" (a) For tannin. Test a small portion of the clear nontannin filtrate with a 

 few drops of a 1 per cent solution of gelatin. A cloudiness indicates the pres- 

 ence of tannin, in which case the determination must be repeated, using 25 

 grams of hide powder instead of 20 grams. 



" (b) For soluble hide. To a small portion of the clear nontannin filtrate add 

 a few drops of the original solution, previously filtered to remove reds. A cloudi- 

 ness indicates the presence of soluble hide due to incomplete washing of the hide 

 powder. In this case, repeat the determination with perfectly washed hide 

 powder." 



