290 STAIXS AND STAINING. 



have been so far complete as to enable me to place the results 

 before you to-night. The investigation has, however, proved 

 more lengthy than I anticipated, and I am obliged, reluctantly, to 

 hold over this part of the paper for another occasion. 



Iodine Green. 

 Iodine green, or methyl-green, has long been used as a reagent 

 for amyloid, in apparent ignorance of the fact that the reaction 

 really was due to methyl-violet, contained as an impurity in the 

 iodine green. It is exceedingly difficult to obtain a green quite 

 free from violet. As far as I know, there is not a single maker at 

 the present time wbfe can supply it ; but I have here a sample 

 obtained some years ago by Dr. Warwick, which is practically 

 pure, and with which the amyloid violet cannot be produced. 

 The presence of violet in these greens can be very simply 

 demonstrated. Here are samples of iodine green and methyl- 

 green dissolved in water ; to these will be added sufficient caustic 

 alkali to decompose and so decolorise the green, when the 

 residual violet will be plainly seen. 



% 



Cellulose Reactions. 



After the nuclear stains, probably the most important reagents 

 to the worker in botany are those which affect cellulose and its 

 modifications. Pure cellulose is coloured yellow by iodine, the 

 colour being changed to a blue on the addition of slightly diluted 

 sulphuric acid (about 2 volumes of strong acid to i of water), or 

 a strong solution of chloride of zinc. 



Schulze's Solution. 



This solution, containing iodine, iodide of potassium, and 

 chloride of zinc, gives a violet reaction with unaltered cellulose, 

 and yellow with lignified cellulose. 



In working out the best formula for Schulze's solution some 

 rather peculiar points were noticed, which are sufficiently interest- 

 ing to be placed on record. One book-formula reads as follows : 

 Zinc is dissolved in hydrochloric acid ; the solution is allowed to 



* This reaction is the same for both greens, which really differ only in 

 name. Formerly it was customary to use methyl iodide in the manufacture of 

 this dye, hence the names "methyl-green," and " iodine green " is rather a 

 misnomer, although both names are still used by the dealers. 



