IODINE AND ALCOHOL 31 1 



from iodine heated in a test-tube. Algae may be fixed by placing 

 a few crystals of iodine in the bottom of a test-tube, cautiously 

 inclining the tube slightly with the mouth downward, then 

 placing the algae in the test-tube near the mouth directly from 

 the water in which they were growing, and thereafter heating 

 the crystals so that the fumes from them pour down over the' 

 algas. The iodine may afterward be expelled by warming the 

 fixed material to 30 or 40 C., and the material will then need 

 no further washing out. 



Iodine has a wide application in plant histology and micro- 

 chemistry. See under Aconitine, Atropine, Carotin, Cellulose, 

 Colchicine, Gums, Gram's Method, Lipochromes, Lignin, 

 Nicotine, Proteids, Starch, Suberin. 



Iodine and Alcohol. A good fixative for very small organ- 

 isms is a solution of 3 parts of iodine in 100 parts of 70 per 

 cent, alcohol. This at the same time permits the staining 

 effect of iodine on the cell-wall and cell-contents. 



Iodine and Glycerine. A mixture of potassium iodide- 

 iodine with glycerine in equal parts gives good results when 

 the action of iodine is to be observed. The glycerine keeps 

 the preparation from drying and at the same time has a clear- 

 ing effect. 



Iodine and Phosphoric Acid. Used as a test for cellulose, 

 which it colors violet. Prepared by dissolving with heat 0.5 

 gm. of potassium iodide and a few crystals of iodine in 25 c.c. 

 of concentrated aqueous solution of phosphoric acid. 



Iodine and Potassium Iodide. This solution is prepared 

 by dissolving 0.5 gm. of potassium iodide and i gm. of iodine 

 in a small amount of water, and then diluting this with 100 

 c.c. of water. The solution is left standing over any iodine 

 which may crystallize out. This formula is recommended by 

 Arthur Meyer in his work on "Starkekorner" as best adapted 

 to the study of starch grains. A rough-and-ready method of 

 preparing an iodine solution is to dissolve a small amount of 

 potassium iodide in distilled water and then dissolve crystals 

 of iodine in this until a brown color is obtained. This can be 



