Carbon Assimilation. 
9i 
subsequent separation of the watery methyl alcohol layer. The 
methyl alcohol is completely removed hy further washings with 
water. The xanthophyll solution is then passed through a filter 
into a 100 c.c. measuring flask. 
The solution is then cleared with a few drops of absolute alcohol 
and ether added up to the 100 c.c. mark. 
The petrol ether solution of carotin is similarly washed, cleared 
and made up to 100 c.c. 
4. The Standard Solutions. The Chlorophyll Components. 
The standard solution of the chlorophyll components are prepared 
by the saponification of a mixture of the methyl phseophorbides as 
follows : 
(M)369 grams Methyl phaeophorbide a (half hydrate) 
(12 x 10~ 5 gm.-mols. per litre); 
0 , 0124 grams Methyl phaeophorbide b (water-free) 
(4 x 10 —6 gm.-mols. per litre). 
The mixture is dissolved in 2 c.c. of pyridine and saponified with 35% 
methyl alcoholic potash in the manner described above, under (2), 
only as pure substances are used it is unnecessary to go through 
the treatment for purification with 12 and 20% acid. This gives 
about 500 c.c. phytochlorin e in ether saturated 3% acid, and of 
phytorhodin g in 12% acid. 
These solutions can be kept for about a week, but after a 
longer time the colours change somewhat. In such a case the 
comparisons are better if the experimental solution is allowed to 
stand for a day. 
The Yellow Pigments. The carotin solution is made up with 
petrol ether and the xanthophyll with ether, as follows : 
0 0134 grams carotin in 500 c.c. petrol ether containing a little 
ether (5 X 10 -s gm.-mols. per litre). 
0'0142 grams xanthophyll in 500 c.c. ether (5 x 10~ 6 gm.-mols. 
per litre). 
The carotin solution can be kept in a well stoppered bottle in 
the dark for at least three weeks. The xanthophyll solution must 
be made fresh every day as it bleaches quickly, perhaps on account 
of impurities in the ether. 
Instead of using solutions of the actual pigment it is possible to 
employ a solution of potassium dichromate as a standard solution. 
Willstatter gives the following thicknesses of aqueous potassium 
