ANNUAL REPORT, 1941 31 



tent, concentration, and rate of flow of acid and starch can be regulated. An 

 electrometric titration method for measuring small concentrations of acid in starch 

 has been satisfactorily worked out. Apparatus for heating the acidified starch 

 under thermostatic control, uniform agitation, and a controlled atmosphere of 

 air, carbon dioxide, or nitrogen has been designed and constructed. 



There exists a real need for an adequate description or definition of the different 

 grades and types of modified starches. This problem has been approached by 

 studies on the physical and chemical properties of commercial dextrins. Analyses 

 for moisture, reducing sugar, copper-reducing power, alkali lability, solubility, 

 iodine color, ash, bound water are in progress on a series of commercial samples 

 and their fractions. Characterization of dextrins by the ratios of significant 

 fractions is also under investigation. Several dextrins have been fractionated by 

 alcohol and the dextrin acetates have been fractionated by organic solvents. 

 Characterization of the dextrin fractions is being carried out by end group assays 

 and viscosity-molecular weight determinations. 



Studies of the physical and chemical properties of the starches have begun 

 with an examination of the phosphorus content of several starches. An electro- 

 dialysis technique was developed for quantitatively measuring the inorganic 

 and the organically bound phosphorus in natural starches and in phosphorylated 

 starches. Since size of starch grains is believed to be a factor influencing the 

 character of the manufactured dextrins, a grain size classifier for separating large- 

 grain and small-grain fractions has been designed. Since water relations play 

 an important role in the conversion of starch, studies have been continued on 

 the bound water and free water relationships. 



Several methods for determining the bound and free water ratio in starch 

 have shown that potato starch suspensions contain about .3 gram of bound water 

 for each gram of dry starch. Canadian and Russian workers have reported 

 anomalous heat capacities for suspension of hydrophyllic colloids and these data 

 were interpreted as indicating a lower specific heat for bound water thus affording 

 a new method for measuring the bound water. Similar data were collected in this 

 laboratory for starch water suspensions. Careful analysis cf the data, however, 

 shows definitely that the above interpretation is erroneous. The anomalous 

 behavior of the starch water suspensions can be accurately described by linear 

 equations embracing a discontinuity at the point where all the water in the 

 starch suspension is bound. An explanation ol this phenomenon is awaiting veri- 

 fication by experiments on other systems of hydrophyllic colloids. 



Investigations on the Nutritive Value of Fishery Products as Human and Animal 

 Food. (Monroe E. Freeman and W. S. Ritchie.) The Progressive Decomposition 

 of Fish Muscle. Studies on the first stages of protein decomposition in fish muscle 

 (Annual Report — 1940) were followed by investigation of more extensively de- 

 composed muscle tissue. About twenty-five different fractions were isolated as 

 p'crate derivatives from one large sample of haddock muscle. None of these 

 compounds nor their derivatives exhibited clearly defined melting points. Con- 

 sequently their identification depends on ultimate analyses for carbon, hydrogen, 

 and nitrogen; and determination of molecular weights. Since many of these 

 picrates are violently explosive, special techniques have been devised to facil'tate 

 semi-micro combustion and Dumas analyses. 



The Influence of Base Exchange Capacity and of Exchangeable Ions in Massa- 

 chusetts Soils on the Availability of Potassium. (Dale H. Sieling.) As a fore- 

 runner to the actual investigation of soils collected for this study it seemed ad- 

 visable to use the soils most readily obtainable in large quantities for physiological 



