MICK CHE MIS TRY. 95 



/. Potassium Myronate, KC 10 H 18 NS S O 10 . 



156. Potassium myronate, which occurs in the seeds of 

 many Crucifercz, is split up by the ferment myrosin into the 

 allylene mustard-oil, glucose, and potassium sulphate. For 

 its microchemical recognition Guignard (II) first treats sec- 

 tions with alcohol, which dissolves out any fatty oil and 

 makes the myrosin inactive, while potassium myronate is 

 almost insoluble in it. If the sections are then placed in an 

 aqueous extract of white mustard-seed, which is very rich in 

 myrosin, there is formed in the cells containing myronic 

 acid the allylene oil of mustard, which Guignard recognizes 

 by the aid of tincture of Alcanna (cf. 109). 



g. Phloridzin, C 21 H 24 O 10 . 



157. O. Herrmann (I, 21) uses for the microchemical 

 recognition of phloridzin, solutions of ferric chloride and 

 ferrous sulphate. The former produces a dark red-brown 

 solution, the latter a yellow-brown precipitate. These 

 reactions have led to trustworthy results only with Pirus 

 Malus ; in case of the pear, cherry, and plum, they are too 

 much masked by the presence of large quantities of tannin 

 which gives a green color with iron salts. 



h. Ruberythric Acid, C 26 H Q8 O 14 . 



158. Ruberythric acid forms the chief constituent of the 

 so-called madder dye in the roots of Rubia tinctorum, and is 

 decomposed, on boiling with hydrochloric acid, into glucose 

 and alizarine (cf. Husemann I, 1387). It has a yellow color 

 and, as Naegeli and Schwendener (I, 502) have shown, is 

 exclusively dissolved in the cell-sap in young roots, while 

 the membranes are still quite colorless. In older roots the 

 membranes are, however, colored, even in such as are still 

 living, as Naegeli and Schwendener showed by plasmolysis 

 of the cells. 



Caustic potash solution colors the mixture of coloring 

 matters in Rubia tinctorum purple-red, acids color it orange, 

 ferric chloride, orange to brown-red. When the roots dry, 



