11 REAGEXTX. 



Chlor-iodide of Zinc. 



This is known as Schulze's reagent and is very useful in 

 detecting the presence of cellulose. This reagent is made by pour- 

 ing over metallic zinc some hydrochloric acid and then evaporating 

 the solution with an excess of zinc present, until it becomes of a 

 thin syrupy consistency. Add as much iodide of potassium as 

 will be taken up, and then iodine until a saturated solution is 

 obtained. Keep the reagent in the dark to prevent the formation 

 in it of hydriodic acid. 



Pure cellulose gives with this reagent a blue or violet color, 

 due to the staining by the iodine of the amyloid which is formed 

 by the action of the agent on cellulose. Wood, cork, and cutinized 

 walls are colored yellow, while starch colors blue, but the grains 

 soon become disorganized. Cells containing tannin are colored by 

 the reagent red or violet. Fungus cellulose, unlike ordinary 

 cellulose, remains uncolored by the action of this agent. 



