SPECIAL METHODS. 14! 



white salt, in somewhat less than its own weight of water, 

 and then adding sufficient metallic iodine to give the solu- 

 tion a deep sherry-brown color. I prefer Griibler's prepara- 

 tion of the chloroiodide.] These solutions remain for a long 

 time unchanged, especially when kept in the dark. The 

 reaction succeeds best when the sections are placed directly 

 in the concentrated reagent. 



5. Recently a number of reagents containing iodine have 

 been recommended by Mangin (VII), which act in the same 

 manner as chloroiodide of zinc and seem to be, in part, 

 more delicate than it. 



Of these reagents I have used with good results a calcium- 

 cJiloride-iodine solution, and, instead of following Mangin's 

 somewhat more elaborate method, have prepared it by 

 adding about .5 gram of potassium iodide and .1 gram of 

 iodine to 10 ccm. of a concentrated solution of calcium 

 chloride and then, after gentle warming, separating the 

 solution from the excess of iodine by filtering through 

 glass-wool. 



This solution, in which the sections should be placed 

 directly, colors lignified membranes yellow to yellow-brown, 

 but pure cellulose walls become first rose-red and, after a 

 time, violet. According to Mangin, it should be kept in 

 the dark. 



By the aid of iodine-phospJioric acid recommended by 

 Mangin, one obtains a very deep violet coloring of cellulose 

 walls, while lignified and suberized walls are colored yellow 

 or brown. This reagent is prepared by adding a small 

 quantity of potassium iodide (about .5 gram to 25 ccm.) and 

 a few crystals of iodine to a concentrated aqueous solution 

 of phosphoric acid, and gently warming the whole. The 

 sections should be freed of all water adhering to their sur- 

 faces, by means of filter-paper, before being placed in this 

 solution. 



Mangin also recommends mixtures of aluminium chloride 

 or stannic chloride with iodine and potassium iodide. For 

 the manner of preparing and using these solutions, Mangin's 

 work may be consulted. 



