76 BOTANICAL MICROTECHNIQUE. 



the related compounds, will be discussed in Part III of this 

 book (cf. 242-297 and 400-415). 



117. But before we enter upon the special reactions of the 

 soluble carbohydrates, two reactions common to many can- 

 bohydrates may be described. These were introduced into 

 microchemistry by Molisch (V), and at first especially for 

 the recognition of species of sugar. The reagents used are 

 #-naphtol and thymol. 



Molisch uses a-naphtol by treating sections not too thin, 

 on the slide, with a drop of a 15-20$ alcoholic solution of 

 the compound and then adding two or three drops of con- 

 centrated sulphuric acid, so that the sections are wholly 

 covered. In the presence of cane-sugar, milk-sugar, glucose, 

 laevulose, maltose, or inulin, the section becomes colored a 

 beautiful violet in a short time (about two minutes), while 

 this reaction does not occur with inosite, mannite, melam- 

 pyrite, and quercite. 



If thymol be used in the same way intead of <*-naphtol, a 

 carmine-red color is produced. 



Concerning this reaction it should be said that the con- 

 centrated sulphuric acid contained in the reagent may split 

 off sugars from glucosides, starch, cellulose, and various 

 other substances, and these may then give the reaction in- 

 directly. But in the absence of soluble carbohydrates the 

 reaction occurs much later, often only after a quarter to a 

 half of an hour. Then, too, according to Molisch, one may 

 reach a definite conclusion as to the presence of soluble car- 

 bohydrates by treating in the same way a fresh section and 

 one extracted with boiling water. If the reaction occurs 

 markedly sooner in the former, it is proved that it depends 

 upon the presence of soluble substances. 



But it has been shown by Nickel (I, 31) that, besides the 

 compounds mentioned, a number of bodies of wholly differ- 

 ent constitution give the same reaction, especially proteids, 

 kreatin, and vanillin. According to Nickel, it is very prob- 

 able that these reactions depend upon the fact that the sul- 

 phuric acid splits off furfurol from the compounds named. 



