BOTANICAL MICROTECHNIQUE. 



membranes, any ash constituents being, of course, quite 

 disregarded. 



246. For the microchemical recognition of the cellulose 

 membranes the following reactions are used : 



1. Solubility in concentrated sulphuric acid. This begins 

 with a strong swelling, which finally passes into complete 

 solution. 



2. Solubility in cuprammonia. This reagent, which is also 

 known as Schweizers reagent, may be prepared by precipi- 

 tating cupric oxyhydrate from a solution of cupric sulphate 

 with a dilute solution of caustic soda, then washing the pre- 

 cipitate with water by repeated decantation and filtering, 

 and finally dissolving it in the most concentrated ammonia- 

 water. 



A very good reagent may be more simply prepared by 

 pouring 13-16$ ammonia-water over copper turnings and 

 letting the whole stand in an open bottle (cf. Behrens II, 



55)- 



Cuprammonia can be preserved for only a limited time. 

 To test its fitness for use, one may use cotton, which it 

 should completely dissolve at once. 



3. The blue color with iodine and sulphuric acid. Ac- 

 cording to Russow, this reaction may be best conducted by 

 treating the sections first with an aqueous solution of J$ 

 iodine and \\% potassium iodide, and then adding a mixt- 

 ure of two parts concentrated sulphuric acid and one part 

 water. 



4. The violet color with chloro'iodide of zinc. This re- 

 agent is usually prepared by dissolving an excess of zinc in 

 pure hydrochloric acid and then evaporating the solution to 

 the density of sulphuric acid in the presence of an excess of 

 metallic zinc ; the solution is then saturated with potassium 

 iodide and finally with iodine. The chloro'iodide may be 

 more simply prepared by dissolving 25 parts of zinc chloride 

 and 8 parts of potassium iodide in 8.5 parts of water, and 

 then adding as much iodine as will dissolve (Behrens II, 54). 

 [I have used with excellent results a preparation obtained 

 by dissolving solid commercial chloro'iodide of zinc, a moist 



