METABOLIC PROCESSES IN THE PLANT. 361 



We fill a beaker with dilute Copper sulphate solution. In this 

 we suspend a glass tube about 6 cm. long and wide, closed at 

 both ends with parchment paper, and filled with water, into which 

 a spiral of zinc has been introduced. The solution of Copper 

 sulphate penetrates into the tube, and distributes itself in the 

 water ; but when it comes into contact with the Zinc it is decom- 

 posed, and forms soluble Zinc sulphate, while the Zinc becomes 

 coated with a gradually thickening crust of metallic Copper 

 and Copper oxide. The accumulation of Copper in the tube is 

 thus easy to prove. 



That dissolved substances can be separated from their solvents, 

 and stored up by bodies capable of imbibition, may be demon- 

 strated as follows : We treat water with a few drops of an 

 alcoholic solution of Iodine, so that the fluid assumes a yellowish 

 colour, and add to it some wheat starch. This last takes up the 

 Iodine. It consequently becomes blue in colour, while the fluid 

 is rapidly decolorised. We further provide a glass funnel with 

 six or eight filter papers, placed one within the other, and pour 

 on them a dilute aqueous solution of methyl violet. The paper 

 completely arrests the pigment. A colourless fluid runs from 

 the filter. 



