286 REAGENTS AND PROCESSES 



as a reagent is prepared by placing alcanna root in 95 per cent, 

 alcohol for about ten hours, or until a deep red solution is ob- 

 tained, and then filtering off the solution and diluting it with an 

 equal bulk of water. 



(i) Suberized and cutinized walls, when treated with a solu- 

 tion of alcannin for some hours, take on a pink color. (2) 

 Alcannin tincture mixed with i per cent, glacial acetic or formic 

 acid is used to fix and stain sections of elaioplasts from fresh 

 material. (3) When sections containing fatty oils are treated 

 with tincture of alcannin, the oil is colored pink. Sections 

 containing ethereal oils and resins behave in the same manner. 



Alcohol. — The commercial alcohol obtained in this country 

 is about 95 per cent, alcohol. In making alcohols from this 

 of different strengths it answers all practical purposes to pro- 

 ceed as if the commerical 95 per cent, alcohol were absolute — 

 that is, very nearly 100 per cent. Thus, if 50 per cent, alcohol 

 is desired, 50 c.c. commercial alcohol and 50 c.c. distilled water 

 will give sufficiently accurate results fot all histological work. 

 If absolute alcohol is desired, it may be prepared by pouring 

 the commercial alcohol over unslacked lime, and then distilling 

 from this. Or better still, drive off the water of crystalliza- 

 tion from copper sulphate by heating in an iron vessel. Put 

 the powder into a bottle and pour 95 per cent, alcohol over it. 

 Keep the bottle tightly stoppered. Water will be extracted 

 from the alcohol and absolute alcohol results. 



Ammonium Molybdate. — A concentrated solution of am- 

 monium molybdate in a saturated solution of ammonium chlo- 

 ride. This gives a yellow precipitate in sections containing 

 tannins. 



Ammonium Vanadate. — This is used as a test for solanin. 

 The sections are treated with a solution prepared by dissolving 

 I part of ammonium vanadate in 1000 parts of a mixture of 

 98 parts of concentrated sulphuric acid and 36 parts of water. 

 If solanin is present, a yellow color appears, which merges into 

 orange, then different shades of red, and finally into violet, and 

 then all color disappears. 



