204 CAROTINOIDS AND RELATED PIGMENTS 



pletely adsorbed, leaving the carotin in solution. Any carotin held 

 mechanically by the adsorbing material can be washed out with 

 petroleum ether without removing the adsorbed chlorophyll. It would 

 seem entirely practicable to apply these facts to the isolation of crys- 

 talline carotin from leaves. The removal of the chlorophyll could be 

 postponed until the bulk of the petroleum ether was distilled off and 

 before the final concentration and crystallization of the pigment. 

 According to the laws of adsorption it may be expected that the ad- 

 sorbing material will also remove a certain amount of some of the 

 other impurities. In applying this method care must be taken to 

 choose only the most finely divided adsorbing agent. 



The problem of securing pigment solutions from fresh or dried plant 

 tissues merely for macroscopic examination is much less compli- 

 cated. Fresh tissues should first be macerated. Tswett recom- 

 mends the use of a little CaCO :! or MgO in connection with the 

 maceration to neutralize the acids in the plant sap. In order to 

 choose the proper solvent it is well to have in mind certain rules 

 laid down by Tswett (1906b) for the action of the various solvents 

 upon the carotinoid and chlorophyll pigments in plants. According 

 to Tswett the solvents commonly used are divided into three groups 

 according to their relations toward the leaf pigments. 



1. Alcohol (methyl, ethyl, amyl), acetone, acetaldehyde, ether, 

 chloroform. These solvents acting on fresh (macerated) or dried 

 leaves dissolve out all the pigments equally and completely. 



2. Petroleum ether and petroleum benzine (low or high b. p". petro- 

 leum ether). Fresh leaves (macerated) give more or less yellow 

 extracts when treated with these solvents. The chief pigment is carotin 

 but traces of other pigments are also extracted. Leaves dried at 

 low temperature likewise give up their carotin to these solvents, and 

 in somewhat purer condition. Plant tissues which have been cooked, 

 or only warmed to a moderately high temperature, however, give 

 green extracts when macerated with these solvents. 



3. Benzene, xylene, toluene and carbon disulfide. These solvents 

 act intermediately between the first and second groups. For the 

 extraction of all the chlorophyll and carotinoid pigments Tswett recom- 

 mends petroleum ether containing 10 per cent absolute alcohol for 

 fresh leaves and petroleum ether containing 1 per cent alcohol for 

 dry leaves. 



Animal fat. It is manifestly impossible to secure carotin in appre- 

 ciable quantities from animal fat, like butter fat, or from the highly 



