CHANGES IN METHODS FOR THE ANALYSIS OF TANNING MATERIALS. 



Page 77, 1. reparation of sample. Add at bottom of page: "Extracts must be 

 heated in ."() . well shaken, and allowed to cool slowly to room temperature/' 



Pag.- 7s. 'A. Drhrmi nation of moisture. First line, insert "5" instead of "2." 



P:i<_re 7S, 4. Oiiantity of tnnnlny material. Substitute the following: "In the case 

 of barks, woods, leaves, etc., use such an amount of the material as to give about 1 

 gram of total solids per 100 cc of solution, and extract in a Soxhlet or similar appa- 

 ratus. In the easo of extraets. use, 20 grams, dilute with water at 80, cool slowly to 

 20, and make volume up to a liter." 



Page 78, 5. Determination of total solids. First line, insert after "and." "without 

 filtering." 



First line, take out comma and insert period after "pipette," and add sentence, 

 "Care must be taken to keep the solution at 20." 



Pair's. <>. Determination of soluble solids. Substitute the following : " Filter about 

 125 (< of tin- solution measured, at 20, through a double folded filter (S. and S. No. 

 590,25 em), returning the filtrate through the filter twice. Evaporate 100 cc as 

 before." 



Pa'_rr 7 s . 7. Determination of tanning substances. Substitute the following: "Pre- 

 pare 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 Avater 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 Aveight at 100. Add the remainder of the hide powder to 200 cc 

 of the original 1111 filtered solution at 20, and shake for ten minutes. Add 5 grams 

 of barium sulphate free from soluble salts, and shake again for one minute. Filter 

 immediately through a folded filter (S. and 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 recommended." 



Pa. -.re 78, 2. Telling the It ide powder. Substitute the following: 



"(a) Shake 10 grams of the hide powder with 200 cc of water for five minutes; 

 filter through muslin or linen; squeeze out thoroughly by hand; collect the hide 

 powder, and repeat the operation twice with the same quantity of water. Pass the 

 last filtrate through paper until a perfectly clear liquid is obtained. Evaporate 100 

 << of the final filtrate in a weighed dish; dry at 100 until the weight is constant. 

 If the residue amount to more than 10 mg, the sample should be rejected. The hide 

 powder must be kept in a dry place and tested once a month. 



"(b) Prepare a solution of pure gallotannic acid by dissolving 5 grams in 1 liter 

 of water. Determine the total solids by evaporating 100 cc of this solution and 

 drying to constant weight. Treat 200 cc of the solution with hide pOAvder exactly 

 as described in paragraph 6. The hide powder must absorb at least 95 per cent of 

 the total solids present. The gallotannic acid used must be completely soluble in 

 water, alcohol, acetone, and acetic ether, and should contain not more than 1 per 

 cent of substances not removed by digesting Avith excess of yelloAv mercuric oxid on 

 the steam bath for two hours." 



Page 78, add the following: 



"8. TESTING THK NOXTAXXIX FILTRATE. 



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

 drops of a 10 per cent solution of gelatin (Nelson's). A cloudiness indicates the 

 presence 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 cloudiness indi- 

 cates the presence of soluble hide due to incomplete Avashing of the hide powder. 

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



