INVESTIGATION OF 1905. 9 



as a rule, higher than those obtained and published a few years ago, 

 when rarely more than 25 per cent of tannin was determined in even 

 the best Sicilian sumac. The high results here reported, which are 

 now obtained quite generally by others, are probably due, therefore, 

 to more complete extraction and improved methods of analysis 

 rather than to improvement in the quality of sumac. It has been 

 the opinion among tannery chemists, based on the work of Semour- 

 Jones, Palmer, Parker, and Proctor, of England, that most tanning 

 materials are best extracted a*t temperatures below boiling; thus 

 sumac is supposed to yield the highest results by extracting below 

 60 C. The work done in the Bureau of Chemistry makes this 

 opinion no longer tenable, as the highest results have been obtained 

 at from 60 to 90 C. according to the following method, which is now 

 used in this laboratory in extracting all kinds of tannery materials. 



Place in the extractor, preparatory to receiving the sample, a per- 

 forated porcelain disk and cover with a mat of asbestos or of purified 

 cotton. Place the weighed sample of tanning material in a beaker 

 and moisten with hot water at from 60 to 90 C. until it has the 

 consistency of a thin paste; then transfer it to the extractor, remov- 

 ing all the material from the beaker with a jet of hot water. Let the 

 water percolate through the extractor into a Jena boiling flask, press 

 the material down well, cover with a perforated porcelain plate, and 

 return the percolate to the extractor until it runs clear. Allow a 

 total volume of from 300 to 400 cc to percolate at a temperature of 

 from 60 to 90 C. Place about 250 cc of fresh water in a clean 

 receiving flask and connect it with the extractor by means of a block- 

 tin condenser, heat to boiling, and finish the extraction at steam heat, 

 replacing the extract with fresh portions of water two or three times 

 and being careful to keep the total volume of extract within a liter. 

 When the extraction is completed, usually in from twenty to twenty- 

 five hours, combine the hot extracts in a liter flask and make up to 

 volume when cold. Only the best nonsoluble glass and block tin 

 must be used in the extraction apparatus, as the alkali dissolved 

 from ordinary glass materially dissolves "reds" insoluble in cold 

 water. Make the determination of tannin and, other constituents of 

 the extracts according to the official methods of the Association of 

 Official Agricultural Chemists. a 



Determine the moisture by drying 5 grams of substance in a flat- 

 bottomed dish for five hours and check the weight again after drying 

 for three hours. 



Determine the crude ash in the residue from the moisture by incin- 

 eration at a low red heat until all carbon is burned away, then cool 

 and weigh the residue. 



a U. S. Dept. Agr., Bureau of Chemistry, Bui. 107, p. 35. 

 48524 Bull. 11708 2 



