CH. XIl] TANNINS. 249 



Tannins and Glucosides. 



These substances will be completely extracted by 

 alcohol of '850 Sp. G., and will therefore be present in the 

 alcohol extract. (Extract No. II.) 



After evaporating off the alcohol, taking up with 

 water and filtering, the solution has to be examined for 

 tannins, glucosides, and sugars, but the whole of the 

 sugars will rarely be present in this solution. 



Some proteids may pass into this solution but they 

 are generally rendered insoluble by the treatment, and if 

 they are found to be present after removing the tannins 

 they can be precipitated by alcoholic mercuric chloride 

 (as in removing peptones) before examining for sugars : 

 small quantities of amides if present may be neglected. 



It sometimes happens that the solution is rather 

 strongly acid, in this case it should be exactly neutralised 

 with dilute soda before commencing examination. 



Under the heading of tannins and glucosides are 

 mcluded a large number of different compounds which are 

 in many respects widely different in properties, although 

 possessing certain characters in common, and it is conse- 

 quently rather difficult to give general instructions. 



It is assumed, in treating of these compounds, that it 

 is not desired to make experiments concerning their rela- 

 tions to metabolism ; but from any point of view it is of 

 the greatest importance that the processes for their com- 

 plete removal from solution should be thoroughly studied. 

 Tannins and most glucosides readily give the reduction 

 of Fehling's, Sachsse's, and the other solutions commonly 



