INORGANIC SALTS. 35 



only slightly suberiferous will, therefore, hardly 

 show this reaction ; and to detect their suberin, 

 the sections are placed in the cold fluid a few mo- 

 ments, and then removed to a solution of potash. 

 The walls, which after the first treatment stand out 

 sharply, assume an ochre-yellow color under the 

 action of the potash -. in all cases after being 

 slightly warmed. 



CUPRIC SULPHATE (Blue Vitriol). 



This substance has a very extensive application 

 in micro-chemistry. 1 It is always used in a tolera- 

 bly concentrated aqueous solution, and must be 

 chemically pure. 



It is used in the following (Trommer's) test for 

 sugar. A moderately thick section of the tissue 

 which is to be studied is allowed to lie from two to 

 ten minutes in a concentrated solution of the salt. 

 The surface is then rapidly rinsed with distilled 

 water, and the section transferred to a boiling 

 mixture of equal parts by weight of water and 

 potassic hydrate. Cells which contain cane sugar 

 (saccharose) assume a bright blue color, while those 



1 Nageli: Das Mikroskop, 1877, pp. 475, 525. Dippel : Das Mikro- 

 skop, I., p. 372; II., p. 20. Weiss : Allgem. Botanik, 1878, 1., pp. 77, 171,174. 

 Sachs: Flora, 1862, p. 289; Jahrbiicher fur wiss. Bot., III., p. 187. De 

 Vries : Keimung des rothen Klees. Landwirths. Jahrb., 1877, VI., p. 468. 

 Wiesner: Technische Mikroskopie, p. 79. Fresenius: Quantitative chem- 

 ische Analyse, Braunschweig, 1853, p. 496. Fehling: Ann. der Chemie 

 und Pharmacie, Bd. LXXIL, p. 106. 



