CHEMISTRY. 



9 



the reactions for pentosans, yielded considerable quantities of furfurol when distilled 

 with dilute hydrochloric acid — 5.53 per cent from corn pith cellulose and 5.39 per 

 cent from elder pith cellulose, which the author believes was derived from oxycellu- 

 ioses which were either present in the original pith or more jirobably were formed 

 during the oxidation. 



The determination of pentoses and pentosans by means of distillation -with 

 hydrochloric acid and precipitation of the furfurol by phloroglucin, E. Kkober 

 and C. RiMBACH, reported by B. Tollens {Ztschr. Angeiv. Chem.,15 [1902), No. 20, 

 PI). 477-482). — The result of recent investigations of this method are summarized 

 and quite minute directions given as to the distillation, the precipitation of the fur- 

 furol, handling of the precipitate, etc. Hydrochloric acid of 1.08 and 1.1 sp. gr. was 

 found to give somewhat higher results than that of 1.06 sp. gr., but the latter is 

 adhered to as giving the more uniform result. The distillate is treated with an 

 excess of phloroglucin, dissolved in 12 per cent hydrochloric acid, and allowed to 

 stand for 12 to 14 hours, after which the precipitated furfurol-phloroglucid is trans- 

 ferred to a porcelain Gooch crucible, washed with 150 cc. of water, and dried for 4 

 hours in a water bath at 97 to 98°. Krober has found that it is immaterial whether 

 the phloroglucin is absolutely inire or contains a little diresorcin. 



Kr5ber advises transferring the covered crucible to a stoppered weighing glass and 

 placing this in a desiccator to cool, as by this means the hygroscopic phloroglucid is 

 best protected from moisture. Drying for 4 hours is found to be sufficient, and 

 allowing the open cruciljle to stand exposed to the air results in material increase in 

 weight. The principal cause of lack of concordance in the results is the solubility 

 of the phloroglucid in the 400 cc. of precipitant plus the 150 cc. of wash water. 

 Rimbach found in special experiments that 0.005 gm. of phloroglucid was dissolved, 

 and Kr61)er, on an average, 0.00518 gm. The use of a correction of 0.0052 gm. is 

 suggested, and formulas are given on that basis. Krober has prepared a table show- 

 ing the amounts of pentoses and pentosans corresponding to different amounts of 

 phloroglucid from 30 to 300 mg. This table is based upon special determinations 

 made with all possible exactness. The results are generally somewhat lower than 

 those previously given, but the close concordance between the data given by Rim- 

 bach and Krober indicates the correctness of the new figures. A portion of the data 

 are given in the following table: 



Amounts oj pentosans and pentoses corresponding to different amounts of i)hloroglucid. 



Although the above factors represent the greatest exactness as yet obtained by this 

 method. Professor Tollens states that it should be remembered that the present 

 method for pentosan can not be regarded as an absolutely exact one, but only as a 

 conventional method, which is the best we now have. In addition to the pentoses 

 there are other materials, such as oxycellulose and glucuronic acid, which also yield 

 furfurol; and, furthermore, methyl-pen tosans may occur, yielding methyl-furfurol in 

 the distillation, which in turn is precipitated as phloroglucid. These considerations, 

 however, do not prevent the use of the pentosan method as a conventional method, 

 and the employment of Krober' s method of weighing the phloroglucid and the use 

 of his table will give more uniform results. 



