MICR O CHEMIS TR Y. // 



a. Glucose, C 6 H 1Q O 6 . 



In botanical literature the name glucose commonly 

 includes all those kinds of sugar which precipitate cuprous 

 oxide from an alkaline solution of copper. In most cases 

 we have undoubtedly to do with the compound known to 

 chemists as glucose (grape-sugar or dextrose) ; but there are 

 many other substances, as, for instance, laevulose, lactose, 

 and many glucosides, which give the same reaction ; and 

 .great care should be exercised as to the significance of the 

 copper-reaction, where such other compounds are not ex- 

 cluded. 



The reaction named is best conducted, according to A. 

 Meyer (IV), by first placing sections, from two to four cells 

 in thickness, of the object to be studied, in a concentrated 

 aqueous solution of cupric sulphate for a short time, then 

 washing them in distilled water and finally placing them in 

 .a boiling solution of 10 grams of Rochelle salt and 10 grams 

 of potassium hydrate in 10 grams of water. There are then 

 precipitated in the cells containing glucose, vermilion gran- 

 ules of cuprous oxide, whose color may best be seen by dark 

 ground illumination, as they often appear almost wholly 

 black by transmitted light, especially with a narrow cone of 

 rays. Cuprous oxide remains at first unchanged in glycer- 

 ine, even on boiling ; but, according to A. Fischer (V, 74), it 

 is dissolved after some weeks by glycerine, as well as by 

 Canada balsam. 



119. The reaction may also be conducted on the slide in 

 the manner recommended by Schimper (cf. Strasburger I, 

 73), by warming the sections, which should not be too thin, 

 under a cover-glass in a drop of Fehlings solution * 'until 

 little bubbles begin to be formed. Stronger heating usually 

 causes marked changes in the cell contents. 



* Fehling's solution may be prepared, according to Dragendorff (I, 70), 

 by making three different solutions containing respectively, in a liter of 

 water, 35 grams of cupric sulphate, 173 grams of Rochelle salt (sodium- 

 potassium tartrate, NaK(COO) 2 C 2 H 2 (OH) 2 + 4H 2 O), and 120 grams of 

 caustic soda. Just before use, a mixture of one volume of each of these 

 solutions is added to two volumes of water. This mixture becomes changed 

 in time, while the separate solutions may be kept indefinitely. 



