PIGMENTS 113 



mine and the substitution of twenty atoms of this element for the 

 same number of hydrogen atoms. 



The oxygenated carotins are colorless substances, while the 

 iodide crystallizes in beautiful dark-violet prisms, having a cop- 

 pery red fluorescence. ' n^h 



Xanthophyll is closely related to carotin. It has the molecular 

 formula C4oH5oO2. It absorbs 36.55 per cent of oxygen (corre- 

 sponding to 13 atoms, which would indicate the formation of two 

 OH groups an addition to the saturation required by the C n H2n+2 

 formula); and an iodine addition product having the formula 

 C4oH5oO2l2, which crystallizes in dark-violet needles. 



Xanthophyll differs markedly from carotin in its solubilities, 

 being insoluble in petroleum ether and only sparingly soluble in 

 carbon disulfide. It may be fairly easily reduced to carotin. 

 This transformation is reversible, and suggests a similarity to the 

 change from haemoglobin to oxyhaemoglobin, and the reverse, 

 in the blood of animals, as a part of their respiration process. 



Separation of the Chlorophylls, Carotin, and Xanthophyll. 

 These pigments, which exist together in most plant tissues, may 

 easily be separated from each other by taking advantage of the 

 differences in their solubilities, according to the following pro- 

 cedure. Grind up a small quantity of the fresh tissue (leaves of 

 the stinging nettle furnish a conveniently large supply of each of 

 these pigments) with fine sand in a mortar. Cover with acetone, 

 let stand a few moments and then filter on a Buchner funnel. 

 Pour the filtrate into a separatory funnel, add an equal volume of 

 ether and two volumes of water. Shake up once and then allow 

 the ether layer to separate; the pigments will be in this layer. 

 Drain off the water-acetone layer. Now to the etherial solution, 

 add about half its volume of a concentrated solution of potassium 

 hydroxide in methyl alcohol. Shake well and allow to stand until 

 the mixture becomes permanently green. Now add an equal 

 volume of water and a little more ether, until the mixture separates 

 sharply into two layers. The chlorophylls will now be in the 

 lower dilute alcohol layer, and the carotinoids in the upper ether, 

 and may be separated by draining off each layer separately. 

 To separate the carotin from xanthophyll, place the ether solu- 

 tion in a small open dish and evaporate to a small volume. Now 

 add about ten volumes of petroleum spirit and an equal volume 

 of methyl alcohol, stir up well, transfer to a separatory funnel and 



