METHODS OF COFFEE ANALYSES. 907 



dance of furfuraldehyde was obtained, which indicates the presence of 

 some pentose yielding substance. By treatment of a considerable por- 

 tion of the water-insoluble material with a 5 per cent solution of sodium 

 hydroxide, and by precipitation of the extract thus obtained with alco- 

 hol, 1 a gummy substance was obtained. This gum yielded niucic acid 

 by oxidation with nitric acid, an indication of the presence of a galac- 

 tose yielding carbohydrate; by distillation with hydrochloric acid iur- 

 furaldehyde was also obtained, showing the presence of a pentose yield- 

 ing substance in the gum. A galactose and pentose yielding gum has 

 been separated from barley. 2 Whether the gum obtained from coffee is 

 a mixture of galactose and pentose yielding substances, or is a single 

 substance yielding both, has not been determined. 



The residue obtained by evaporation of the sulphuric acid extract of 

 the insoluble material yields an abundance of mucic acid when oxydized 

 with nitric acid, showing the presence of galactose, as stated by Maxwell. 



Satisfactory evidence of the presence of any considerable amount of 

 mannose in the sample of coffee used in the investigation has not yet 

 been obtained. Parallel experiments with coffee and vegetable ivory 

 dust were made. With the latter, an abundant precipitate of mannose 

 hydrazon was obtained; with coffee, the precipitate was not of sum" 

 cient amount for a satisfactory determination of its properties. 



Dierbach 3 isolated the coloring matter of coffee and termed it "coffee- 

 green." 



Coffee also contains traces of volatile oils and about 4 per cent of 

 mineral matter. Potassium salts form a considerable proportion of the 

 mineral matter. Silica, when present, amounts to little more than a trace. 



Kornauth 4 states that in the ash of pure coffees the potash amounts 

 to from 50 to 200 times the soda. 



According to Bernheimer, 5 the products obtained on roasting coffees 

 are palmitic acid, caffeine, caffeol, acetic acid, carbonic acid, hydrochinon, 

 methylamine, pyrol, and acetone. Caffeol is an oil, of the formula 

 CsH,oO 2 , boiling at a temperature of from 195 to 197 C. 



A large number of analyses of coffees have been made, references to 

 which are given in the bibliography accompanying this report. 



METHODS OF ANALYSIS. 



In the detection of adulterants but little chemical work is necessary, 

 hence methods will only be given for the estimation of the principal 

 constituents of coffee. 



Moisture. Dry in a flat dish to constant weight and calculate the moisture as 

 usual. 



Caffeine. The method of estimating this alkaloid in tea (p. 889) may be employed. 



1 A rneteod used for the separation of xylan from wood. 

 2 Lintner and Dull, Chem. Ztg., 1891, 266. 



3 Ann. d. Chem. u. Pharm., 14, 236. 



4 Mittl. a. d. Pharm. lust. u. Lab. f. angew. Chem., Erlangen. Heft 3, 1-56. 

 6 Wien. Akad. Ber. (2 Abth.), 81, 1,032; Jahresb. d. Chern. 1880, 1069. 



