134 



COLLOIDS IN BIOLOGY AND MEDICINE 



In swelling there is a great loss of volume, i.e., the volume of the 

 swollen starch is less than that of the dry starch plus the water 

 necessary for swelling, as was shown in exhaustive experiments by 

 H. RODEWALD.* This contraction is about 8 per cent, when 20 per 

 cent of water is taken up. Swelling is accompanied by the liberation 

 of heat, which, according to E. WIEDEMANN and CHARLES LUDE- 

 KING,* amounts to about 6.6 calories per gram. H. RODEWALD 

 studied the phenomenon more thoroughly and found a diminution 

 in the amount of heat liberated with increasing water content. The 

 following is an abbreviated table of his results: 



If we add more water to starch, and heat to 55-70 C., by "solu- 

 tion swelling," we get a jelly-like mass, starch paste, which dissolves 

 on continued heating in more water. This solution coagulates 

 when it is frozen. G. MALFITANO and A. N. MOSCHKOFF* utilize 

 this property of starch solution to obtain a starch free from mineral 

 substances. Demineralized starch on being mixed with suitable 

 salts shows all the properties of the different forms of starch. These 

 investigators are therefore of the opinion that the various modifica- 

 tions in the properties of the natural starch granules are due to mineral 

 admixtures. 



E. FOUARD,* by means of acids, freed starches from their inor- 

 ganic elements and obtained a substance which formed an unstable 

 colloidal solution in water. Heat, alkalis and alkaline salts made the 

 solution more permanent, whereas cold, acids and acid salts favored 

 jelly formation. On ultrafiltering his starch solutions, E. FOUARD 

 found that in accordance with their concentration, a given fraction 

 of the solution always passed through collodion membranes. He 

 concluded from this, that for every concentration of the starch solu- 

 tion a balance exists between the coarser particles and the molec- 

 ularly dissolved (hydrolyzed?) starches. Unfortunately, the work 

 of E. FOUARD contains no information relative to the permeability 

 of the collodion membranes, so that it is impossible to arrive at any 

 conclusion in reference to the size of the suspended and the dissolved 

 starch particles. 



