554 Proceedings Columbia Biochemical Association [July 



the starch Solution were diluted with lo c.c. of alcohol (95 percent.) 

 and one drop of salt Solution was added. The time required for pre- 

 cipitation and Sedimentation served as a measure of the activity of 

 the various electrolytes. It was shown that the cations in chloride 

 Solutions were effective in the following order : Ba= Sr= Ca > Mg 

 = Ce>Na = K>H> NH4 > Li > Hg" — results which are sim- 

 ilar to ion effects upon many other emulsoids (Hofmeister's " lonen- 

 reihen," etc.). The lower limits of precipitation were as foUows: 

 one drop of o.i w HgClg sol. was without effect ; one drop of 0.025 n 

 LiCl gave a very slight precipitate; o.oi n LiCl, 0.005 ^ NH4CI 

 and 0.0025 n HCl, NaCl, and KCl were without effect; only in- 

 complete precipitation occurred with 0.0025 n sol. of alkali-earth Chlo- 

 rides. If alcohol of varying concentrations (from 80-10 percent) 

 is used, the precipitability of the starch by electrolytes is rapidly 

 decreased with decreasing concentrations of alcohol, and the differ- 

 ence between the effects of the various cations is rendered more 

 marked. A cursory examination of the Sulfates indicated a smaller 

 effectiveness and one or two exceptions to the above order for Chlo- 

 rides. In all cases the precipitation is reversible. Further work will 

 be done on a more accurate differentiation of the cation and anion 

 effects, and upon variations in this phenomenon, with varying de- 

 grees of dispersion of the starch. 



102. Determinations of the acidity of fruit Juices.^ ^ Edgar 

 G. Miller, Jr. In line with Dr. Gies' proposal of the use of diluted 

 vinegar and various " food-acid" media as dentifrices, I have deter- 

 mined the acidity of some common fruit Juices as a preliminary 

 to the selection of the most suitable ones for prophylactic applica- 

 tion to the teeth. The appended data for acidity represent, in most 

 cases, the averages of triplicate results, in c.c. of n/5 sodium 

 hydroxid Solution (phenolthalein) per 10 c.c. of juice: Apple, 3.5; 

 apricot, 3.8; asparagus, 0.9; banana, 2.6; beet (red), i.i; canta- 

 loupe, 0.6; carrot, 0.8; cauliflower, 1.9; celery, 0.8; cherry, 7.6; 

 cocoanut milk, 0.4; cranberry, 19.6; cucumber, i.o; currant, 20.4; 

 gooseberry, 16.2; grape (white), 4.5; grape fruit, 10.3; horse 

 radish, 9.2; lemon, 53.7; orange, 6.y; parsnip, 2.1 ; peach, 6.4; pear, 

 3.2; pineapple, 7.5; plum, 4.8; radish, 0.6; rhubarb, ii.i; straw- 

 berry, 9.3; tomato, 4.2; tumip, 0.6; vinegar, 26.1 ; watermelon, 0.6. 



16 Miller: Dissertation; Columbia University, 1913 (Part iii, p. 25). 



