88 - 



substances such as magnesiao (See Lecture I„) It provides columns that 

 filter uniformly and that do not form deleterious channels even if al- 

 lowed to run dry^-^o 



Columns may also be formed from slurries of the sorbent with the 

 solvent. Compressible powders and especially noncompressible powders 

 such as starch may be packed into columns in this wayo These columns 

 also filter uniformly, but they frequently form channels, and they 

 shrink and become useless if allowed to run dry. 



SORBABILITY OF PIGMENTS 

 Mol ecular Structure end Sorbability 



At the time of Tswett' s experiments, the major structural features 

 of the chloroplast pigments had not been disooveredo Consequently, com= 

 parison of the molecular structure of these pigments with their chroma- 

 tographic behavior in adsorption colxxmns was delayed for some 25 to 50 

 yearso Meanwhile, there were few applications of chromatographic methods 

 to organic substances of known molecular stnicturso As a result some of 

 the first relationships among molecular structure, sorbability and sorp- 

 tion sequences were established with carotenoid pigments. 



Long before Tswett" s chromatographic experiments, the carotenes 



T ft 



had been found to be hydrocarbons »» Their lack of affinity for 

 Tswett' s mild adsorbents could, therefore, be attributed to the absence 

 of polar groups o Many years later when the carotenes were found to be 

 sorbed on the specially activated adsorbents, the molecules of these 

 pigments were found to contain a conjugated system of double bonds, the 

 double bonds occurring alternately with single bonds-'-J -^^^-^^^^o The 

 color or redness of the carotenes, as indicated by the wave lengths of 



