VI. LEATHERS.— TENTATIVE. 

 VEGETABLE TANNED LEATHER. 



1 PREPARATION OF SAMPLE. 



Grind the sample, without undue heating, and pass through a 10 mesh sieve. The 

 ground sample must not contain hard lumps. Plane heavily greased leathers (con- 

 taining more than 20 % fat) into very thin shavings. Spread out the prepared sample 

 an! allow it to return to atmospheric moisture condition; mix thoroughly, and 

 place in tightly covered containers. 



2 MOISTURE. 



Place 10 grams of the sample, as prepared under 1 , in a tared, wide, shallow, weigh- 

 ing bottle (or a similar dish which can be covered tightly), and dry in a water oven 

 for 15 hours at 98^-100°C. Cover the weighing bottle, cool in a desi cator containing 

 sulphuric acid, and weigh. The moisture present in the leather as received may be 

 determined by cutting it quickly into small pieces and drying without grinding as 

 directed above. 



3 TOTAL ASH. 



Incinerate slowly 5 grams of the sample, as prepared under 1 , at a dull red heat. 

 If difficulty is experienced in burning off the carbon, leach the residue with hot 

 water, filter on an ashless filter, dry and ignite the filter and residue, add the filtrate, 

 evaporate to dryness and ignite. Cool in a desiccator containing sulphuric acid and 

 weigh. 



The ash may be examined for acids and bases by any suitable method. Alumin- 

 ium, magnesium, sodium, barium, calcium and lead are the bases, and hydrochloric 

 and sulphuric acids are the acids which it may be necessary to determine. 



4 INSOLUBLE ASH. 



Incinerate slowly the residue from the extraction of water-soluble material, ob- 

 taine I in 6 or 7, until all the carbon is burned off, cool in a desiccator containing 

 sulphuric acid and weigh. 



5 FATS. 



Place, without packing, 15 grams of the leather, as prepared under 1 , in a Soxhlet 

 or Johnson extractor with a layer of fat-free cotton above and below the sample. 

 Extract 8-10 hours with petroleum ether distilling between 50° and 80°C. Heavily 

 greased leathers (containing 15% or more fat) will require the maximum time. Re- 

 move the receiving flask, evaporate the petroleum ether on the stc am bath and dry 

 the fat residue for 3 hours in a water oven at 98°-100°C., cool in a desiccator and 

 weigh. Repeat the drying in the water oven for periods of l-U hours, cooling and 

 weighing as before, until no further loss in weight occurs. Retain the leather 

 residue from the fat extraction for the extraction of water-soluble material in 6 or 7. 



EXTRACTION OF WATER-SOLUBLE MATERIAL. 



6 Method I. 



Evaporate the petroleum ether from the fat-free leather, obtained under 5, and 

 moisten thoroughly with from 100-150 cc. of water. Place a layer of cotton in the 



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