CH. XIl] GLUCOSIDES. 269 



with metallic salts appear to be more or less decomposed 

 by pure water. It is better therefore not to resort to this 

 method unless absolutely necessary. 



Most of the natural tannins resemble in their proper- 

 ties the substance described as mimo-tannic acid (tannin 

 from catechu and various species of Acacia), while they 

 differ from commercial gallotannic acid, which gives 

 several rather peculiar reactions and is not a good type of 

 the general characters of vegetable tannins. 



Phlorogiucin is present in many cases in woody tissues 

 (an account of its distribution is given by Waage, loc. cit. 

 p. 265), but it is not probable that it is a plastic sub- 

 stance. 



It would occur in the alcohol extract if present, and, as 

 it reduces Fehling's, etc. solutions, should be tested for 

 where woody tissues have been extracted. 



It is easily removed if present by shaking with ether 

 before examining for tannins and glucosides, which are 

 not soluble in ether. 



Glucosides. 



After the removal of tannins and proteids (if present) 

 portions of the solution may be tested for glucosides if it 

 is supposed they are likely to be present. 



The reactions and solubility of the various glucosides 

 likely to occur must be studied, and if they can be 

 removed by shaking with an immiscible solvent it is best 

 to proceed in this way (the process should be carried out 

 in the same way as in removing tannins with acetic ether). 



If a glucoside should be present which is not removed 



