356 MICROCHEMISTRY OF PLANT PRODUCTS 



The tissues of the pear, cherry, and plum are apt to contain 

 large amounts of tannins which produce a green color with salts 

 of iron, and so mask the phloridzin reaction. 



Phloroglucin, C6H3(OH)3. — This occurs in solution in the 

 cell-sap. To demonstrate its presence treat previously dried 

 sections with a solution prepared by dissolving 0.005 g"^- of 

 vanillin in 0.5 gm. of alcohol, and adding 0.5 gm. of water and 

 3 gm. of concentrated hydrochloric acid. When phloroglucin 

 is present, this solution produces a light red color. 



Phosphoric Acid, H3PO4. — This can be best demonstrated 

 in the ash. The ash is dissolved in hydrochloric acid and the 

 solution is evaporated to dryness; then the residue is treated 

 with ammonium molybdate, which, if phosphoric acid is pres- 

 ent, produces a precipitate of ammonium phospho-molybdate, 

 the crystals of which have a greenish-yellow color under the 

 microscope. If the presence of phosphoric acid is to be sought 

 for in fresh tissues, sections should be heated in a drop of am- 

 monium molybdate on the glass side. This method also pro- 

 duces a precipitate of crystals of ammonium phospho-molybdate 

 in the presence of phosphoric acid. If ammonium tartrate is 

 present in the tissues, ammonium molybdate does not serve so 

 well as a test for phosphoric acid. In such a case a solution 

 should be used, consisting of 25 volumes of a concentrated aque- 

 ous solution of magnesium sulphate, 2 volumes of a concentrated 

 aqueous solution of ammonium chloride, and 15 volumes of 

 water. With phosphoric acid this solution produces a precipitate 

 of ammonio-magnesium phosphate the crystals of which are 

 frequently formed in x- and *-shaped clusters. 



Phycoerythrin. — The red coloring matter in the Florideae 

 or red algae. It is soluble in fresh water, leaving chlorophyll 

 behind in the plastids, while in ether the chlorophyll is extracted 

 and the phycoerythrin is left. 



Phycocyanin. — The blue coloring matter in the blue-green 

 algae. It is soluble in cold water, glycerine, and alkalies, giving 

 a blue solution with red fluorescence. It is insoluble in alcohol 

 and ether. 



