28 



University of Xew Hampshire [Sta. Bull. ?>2-\ 



bottom, while Fresenius (13) (1881) reported a method of adding water 

 or salt solution until the specific gravity of tuber and solution was the 

 same, subsequent] \- determining the specific gravity of the solution by a 

 hydrometer. 



American workers also have investigated the relationship between 

 starch content and specific gravity, and have shown the close correlation 

 which exists between these two, notablv W'inton (31) (1887) ; Cutler (12) 

 (1891); Watson (30) (1895); Shutt (21) 1926). 



However, both the European and the American workers have pointed 

 out that while the correlation is close to one, it is not exactly one, and on 

 that account a determination of the specific gravity may not always give the 

 correct value for starch even though it does in the majority of deter- 

 minations. Because of this fact, chemical methods are still considered 

 most reliable even though they are tedious. 



The recent work at this station by Blood and Haddock, and that of 

 Clark, Lombard, and Whiteman (10) (1940), has shown that the reh- 

 tionship between the specific gravity of potatoes and their quality as judged 

 by mealiness is very close. In view of the fact that starch content and 

 specific gravity are also closely correlated, it w^ould appear logical to state 

 that quality is usually dependent on the starch content. 



Because oi the apparent relationship between starch content and (jual- 

 ity as determined by specific gravity, it becomes interesting to know 

 whether Von Scheele's table may be used for estimating the starch con- 

 tent of our American varieties in order that we may relate starch content 

 and quality if desired. A check of this was made by analyzing several 

 Green Mountain tubers of known specific gravity for their starch content. 

 Specific gravity was determined by the use of salt solutions, and starch con- 

 tent was determined by the use of the autoclave method described by Von 

 Scheele. Individual tubers were used for the analysis, and were grated 

 by hand on a common kitchen grater. The pulp was very thoroughly 

 mixed before transferring into covered weighing bottles, and from this 

 point on, the autoclave method was used without modification. A pre- 

 liminary check with pure potato starch had shown that the method was 

 accurate. The results of these few analyses are shown below in ta1)le form. 



TABLE XXVII. Comparison of the starch content of several individual Green 

 Mountain potatoes with that presented by Von Scheele. 



Per cent starch obtained by 

 Von Scheele - page 75 



21.8 

 21.8 

 20.8 

 18.4 

 17.2 

 14.6 

 10.2 



10.0 (calculated) 

 So fi.ilculated) 



The results presented in this table show that Von Scheele's regres- 

 sion line is applicable to our .^mcri^an varieties, provided the per cent o'^ 

 starch is not m-i-ded witbin one or two ]ier ci-nt. As \ On Scheele ex- 



