214 Organic Constituents of Solls [Jan. 



A. A portion of the precipitate is boiled with a little conc. hydro- 

 chloric acid and a few crystals of orcin. If pentosans are present, 

 a green color is prodiiced. A drop of ferric chloride sol. assists in 

 the development of the color. After a strong color has developed, 

 amyl alcohol is added, which absorbs the color f ormed by the reac- 

 tion of orcin and the pentosans. 



B. Some of the precipitate is boiled for a minute with conc. 

 hydrochloric acid and then a sol. of phloroglucin in hydrochloric 

 acid sol. is added. If a red color is f ormed, changing to a violet 

 red, which rapidly darkens due to a fine black precipitate, the pres- 

 ence of pentosans is indicated. 



C. Xylan may be identified by treating with cadmium carbonate 

 and bromine according to the method of Bertrand,^^ and obtaining 

 the characteristic crystals of the double salt : cadmium xylonate and 

 cadmium bromide. 



(20) The alcoholic filtrate from (19) is taken up in a small 

 volume of water, hydrochloric acid is added and the above tests 

 applied for pentose sugars. 



(21) A second portion of the neutral filtrate (15) is precipi- 

 tated with silver nitrate and filtered. The precipitate (22) removes 

 most of the color from the sol. It is washed to remove soluble 

 silver salts, suspended in water and decomposed with hydrogen 

 Sulfide. The sol. is boiled to remove the excess of hydrogen sulfide, 

 filtered and conc. If the filtrate is very dark, reprecipitation with 

 silver nitrate will be necessary. After evaporation to a small vol- 

 ume, and subsequent standing, picoline carboxylic acid,^^ if present, 

 will crystallize out. 



Picoline carboxylic acid: C7H7NO2; slightly soluble in cold 

 water, easily in hot water ; slightly soluble in alcohol and almost in- 

 soluble in ether; crystallizes from water in oblique prisms with 

 water of crystallization, which is lost at 100° C. ; from conc. sol., 

 crystallizes in very thin superimposed plates, forming large scale- 

 Hke masses and giving very brilliant color effects with polarized 

 light; sublimes unchanged on heating in an open dish; does not 

 melt in a capillary tube at 300° C. ; water sol. is acid to litmus ; 



12 Bertrand: Bull. Soc. Chim., 1891 (3), v, p. 556. 



^3 Schreiner and Shorey : The Isolation of picoline carboxylic acid from 

 soils and its relation to soil fertility, Journ. Amer. Chem. Soc, 1908, xxx, p, 1295. 



