ClRCULAfr>NO. 8, REVISED. 



States Department of Agriculture, 



BUREAU OF CHEMISTRY. 



OFFICIAL METHOD FOR ANALYSIS OF TANNING MATERIALS. 



[Report of Committee B., A. O. A. C., October, 1902: W. H. Krug, Chairman; C. A. Browne, 

 C. H. Jones, L. S. Munson, H. D. Haskins. Adopted at the Nineteenth Convention of the Asso- 

 ciation of Official Agricultural Chemists.] 



I. PREPARATION OF SAMPLE. 



Barks, woods, leaves, dry extracts, and similar tanning materials should be 

 ground to such a degree of fineness that they can be thoroughly extracted. 

 Fluid extracts must be heated to 50 C., well shaken, and allowed to cool to 

 room temperature. 



II. QUANTITY OF MATERIALS. 



In the case of bark and similar material, use such quantity as will give about 

 0.85-0.45 gram tannins per 100 c. c. of solution, extract in Soxhlet or similar 

 apparatus at steam heat for non-starchy materials. For canaigre and substances 

 containing like amounts of starch use temperature of 50 to 55 C. until near 

 complete extraction, finishing the operation at steam heat. In the case of 

 extract weigh such quantity as will give 0.35-0.45 gram tannins per 100 c. c. of 

 solution, dissolve in 900 c. c. of water at 80, let stand twelve hours, and make 

 up to 1,000 c. c. 



III. TOTAL SOLIDS. 



Shake the solution, and without filtering immediately measure out 100 c. c. 

 with a pipette, evaporate in a weighed dish, and dry to constant weight, at the 

 temperature of boiling water. 



IV. SOLUBLE SOLIDS. 



Single pleated filter paper (S. and S., No. 590, 15 cm.) shall be used. To 2 

 grams kaolin add 75 c. c. of the tanning solution, stir, let stand fifteen minutes, 

 and decant as much as possible (not on the filter), add 75 c. c. of the solution, 

 stir, and pour on the filter. Keep filter full, reject the first 150 c. c. of filtrate, 

 evaporate and dry next 100 c. c. The portion dried for determination shall be 



^rfectly clear and evaporation during filtration must be guarded against. 



V. NON-TANNINS. 



Prepare 20 grams of hide powder by digesting twenty-four hours with 500 c. c. 

 water and adding 0.6 gram chrome alum in solution, this solution to be added 

 follows : One-half at the beginning and the other half at least six hours before 

 end of the digestion. Wash by squeezing through linen, continue the wash- 

 until the wash water does not give a precipitate with barium chlorid. 

 lueeze thoroughly by hand, and remove as much water as possible by means 

 a press, weigh the pressed hide powder and take approximately one-fourth of 

 for moisture determination. Weigh this fourth carefully and dry to constant, 

 jigh the remaining three-fourths carefully and add them to 200 c. c. of the 

 Original solution ; shake ten minutes, throw on funnel with cotton plug in the 

 Stem, and let drain. Collect this filtrate and filter through folded filter (S. and 



