19121 The Value of Commekcial Starches 137 



300 cc. distilled water added (thus making a 4 per cent, solu- 

 tion) and heated with constant stirring to the boiling point and 

 boiled for ten minutes ; 200 cc. of this solution are then poured 

 into the cup of a Scott viscosimeter, the temperature allowed to 

 become constant, usually 94° C, and 50 cc. run out into a grad- 

 uate, the time being accurately measured with a stop watch. 

 The number of seconds required to deliver 50 cc. of the solution 

 divided by the number of seconds required to deliver 50 cc. of 

 boiling water gives the viscosity.^ 



It will be noticed from this that the starch solution is pre- 

 pared by boiling with water as is done in sizing and finishing 

 and the viscosity is measured at very near the boiling point of 

 the solution, so that the figures obtained show the effect of boil- 

 ing on the different starches. 



The viscosities of the principal commercial starches are 

 shown in the following table. 



Table I. — Viscosities of Commerciai, Starches. 

 (i2 grams starch in 300 cc. water, boiled ten minutes.) 

 Starch Viscosity 



Corn 3.05 



Potato 14.31 



Cassava 3.92 



Sago 1.57 



Wheat 1.25 



Rice i.oo 



From the above table it is seen that there is a wide variation 

 in the viscosities of the different starches and hence a vsdde 

 variation in their value for mill purposes. The viscosity of 

 potato starch is much higher than that of any other starch, but 

 there is also a considerable variation between the viscosities of 

 the other starches. The importance of the viscosity will be seen 

 more fully in the next section in showing the effect of boiling 

 on the viscosity of starch solutions. It has been found that 

 there is frequently considerable variation in the viscosities of 

 different lots of the same kind of starch. It would be very ad- 

 vantageous to the mills for each lot of the same kind of starch 

 to have a uniform viscosity. This would make it possible to 



1 A detail description of this method was published in the Journal of Indus- 

 trial and Engineering Chemistry, Vol. IV, No. 6, 1912. 



