92 Schunck . — The Chemistry of Chlorophyll . 
Notwithstanding its nearly neutral character, however, 
phyllocyanin is capable of yielding compounds of great 
comparative stability, into which metals and acids, more 
especially organic acids, enter as constituents. When phyl- 
locyanin is dissolved in boiling glacial acetic acid it crys- 
tallises out unchanged on the solution cooling. The same 
happens when freshly precipitated cupric oxide or zinc 
oxide is added to a boiling alcoholic solution of phyllo- 
cyanin ; the solution deposits phyllocyanin and there are no 
indications of any combination having taken place between 
the phyllocyanin and the metallic oxide. A very different 
effect is observed when either of the two oxides is employed 
along with acetic acid. When cupric oxide is added to a 
solution of phyllocyanin in boiling acetic acid, the solution 
acquires at once a deep greenish-blue colour, and it no longer 
contains uncombined phyllocyanin, for it shows a different 
spectrum, and on standing it deposits lustrous crystals, which 
consist of a compound of which phyllocyanin, acetic acid, and 
copper are essential constituents. If zinc oxide be employed, 
a similar effect is observed ; the liquid acquires an intense 
green colour, and now contains the corresponding acetate of 
phyllocyanin and zinc. Similar phenomena are seen when 
ferrous oxide, manganese oxide, or silver oxide is taken, 
solutions of various shades of green being obtained, which 
contain phyllocyanin-compounds ; but no similar compounds 
are formed when potassium, sodium, barium, calcium, mag- 
nesium, or lead acetates are employed, for on adding the 
acetate of any one of these metals to a solution of phyllo- 
cyanin in boiling acetic acid, the colour of the latter remains 
unchanged, and phyllocyanin is deposited just as if no metallic 
acetate were present. Acetic acid is, however, not the only 
acid which gives the reaction. If palmitic, stearic, oleic, tar- 
taric, citric, malic, or phosphoric acid be employed, it occurs 
just as with acetic acid, but in some cases time is required for 
its completion. Some combinations, contrary to what might 
have been expected, are without effect ; such are cupric oxide 
and oxalic acid, zinc oxide and oxalic acid, zinc oxide and 
