MICR O CHE MIS TR Y. 115 



excess with the tannins which give a green color with iron, 

 it very quickly stops the reaction. H. Moeller (I, LXIX) 

 used, however, a solution of anhydrous ferric chloride in 

 water-free ether as a reagent for tannin. This is especially 

 adapted to the study of large parts of plants, such as whole 

 leaves or pieces of them. 



Loew and Bokorny (I, 370, note) have recently used for 

 the recognition of tannin in algae a concentrated aqueous 

 .solution of ferrous sulpliate, in which the algae were allowed 

 to be exposed to the air for from twelve to twenty-four 

 hours. I have obtained in this way a very intense reaction 

 in Spirogyra and Zygnema. This may be hastened by warm- 

 ing to 60 C. 



A very rapid reaction is produced by ferric acetate, accord- 

 ing to Moeller (I, LXIX), in the form of the concentration of 

 the officinal tinctura ferri acetici, which contains about 5% 

 of iron or about 2Q% of Fe 2 (C 2 H 3 O 2 ) G . 



ft. Cupric Acetate. 



200. Cupric acetate, which was introduced into micro, 

 chemistry by Moll (I), has the advantage that it forms an 

 insoluble precipitate with tannins. This is brownish in 

 color, but takes, on subsequent treatment with iron salts, a 

 blue or a green color according to the kind of tannin con- 

 cerned. Moll places the tissues to be studied in a concen- 

 trated aqueous solution of cupric acetate and leaves them in 

 it from eight to ten days, or as much longer as may be de- 

 sired. Sections prepared from this material are treated for 

 a few minutes with a 5$ solution of ferric acetate, and, after 

 it is washed out, may be preserved in glycerine or glycerine- 

 gelatine. 



If it is desired at the same time to fix the cell-contents, 

 one may use, according to Klercker (I, 8), a concentrated 

 alcoholic solution of cupric acetate* instead of the aqueous 

 solution. The pieces of tissue should be left several days, 

 at least, in it. 



* This solution must be kept in the dark. 



