THEOBROMINE, DIMETHYL-XANTHIN 365 



molybdate in concentrated ammonium chloride, the same char- 

 acter of precipitate is produced as when potassium bichromate 

 is used. Lead acetate produces a white precipitate with tan- 

 nins. The following method may be employed: Sections are 

 placed in a 7 per cent, solution of copper acetate for about a 

 week or longer, and are then placed on a slide in a drop of a 

 0.5 per cent, solution of ferrous sulphate. After a few min- 

 utes, and before the cell-walls begin to turn brown, the sections 

 are washed in water and transferred to a watch-glass of alcohol 

 to drive out air-bubbles and extract chlorophyll, if any is present. 

 The sections are then mounted in glycerine for examination under 

 the microscope. By this treatment an insoluble brown pre- 

 cipitate is produced in the presence of tannins. The sections 

 may be transferred from the glycerine to glycerine-jelly if per- 

 manent mounts are desired. If the sections are taken from the 

 alcohol in which they are placed to remove the chlorophyll, 

 etc., and placed in a solution of iron acetate, a blue or a green 

 color will be produced, according to the kind of tannin present. 

 If it is desired to fix the cell-contents while testing for tannins, 

 the sections should be placed in a concentrated alcoholic solution 

 of iron acetate instead of in the aqueous solution, as above. 

 When living tissues are placed in a solution of i part of methylene- 

 blue in 500 parts of distilled water, those cells which contain 

 tannins take on a blue color, and later a deep blue precipitate is 

 formed in these cells. Cells containing phloroglucin act in the 

 same way to this reagent as those containing tannins. 



Theobromine, Dimethyl-xanthin, C 7 H 8 N 4 O 2 . This alka- 

 loid occurs in the cocoa-bean and in different parts of several 

 species of Theobroma. Its presence may be demonstrated by 

 the use of hydrochloric acid and chloride of gold, as directed 

 under Caffeine. The reactions for caffeine and theobromine 

 are sometimes difficult to distinguish. When sections contain- 

 ing theobromine are heated in distilled water on the slide to the 

 boiling-point, and the sections are allowed to dry slowly, and 

 a drop of benzol is added to the residue, crystals of theobro- 

 mine appear in the form of a fine powder on the evaporation 



