IRON. 97 



hoi, ether and alkalies, but soluble without effer- 

 vescence in acetic and other acids. The character- 

 istic reaction, however, is the yellow color pro- 

 duced in a dilute neutral solution of nitrate of 

 silver. 



d. Calcium sulphate (gypsum) is insoluble or 

 hardly soluble in hydrochloric, nitric and acetic 

 acids. When crystals of this salt are placed in an 

 aqueous solution of barium chloride they are soon 

 covered by a granular crust of barium sulphate. 1 



IRON 



Has been detected in the cell-wall. 2 The sections 

 must be made with a platinum or silver knife. 

 They are then treated with an alcoholic tincture 

 of sulpho-cyanate of potassium (p. 40), and the ap- 

 pearance of a red color, either immediately or on 

 the further addition of hydrochloric acid, indicates 

 the presence of a ferric compound. In case no 

 reaction occurs the sections are treated with hydro- 



1 N. J. C. Muller claims to have found this salt in Guaiacum wood. 

 (Allg. Bot., 1880, Theil i, p. 557.) Hanbury and Fliickiger, however, only 

 mention calcium oxalate in this plant. ( Pharmacographia, 1874, P- 94-) 

 Nageli (Mikroskop, 1877, p. 486) is of the opinion that it does not exist in 

 the cell at all ; while Wiesner (Techn. Mikroskopie, p. 85) figures the twin- 

 crystals of gypsum from the mesophyll of Iris. Holzner, however, in his 

 classic work on the crystals of plants, shows that the crystals taken for 

 sulphate of lime in Guaiacum, Iris, etc., are in reality the oxalate. The 

 existence of crystals of the sulphate in plants is, therefore, not demon- 

 strated. 



2 Weiss and Wiesner : Sitzungsber. der wiener Akad., 1860, Bd. XL. 

 Cf, Bot. Zeitung, 1860, p. 357. 



