SALT EFFECTS OF PHOSPHATES 



177 



applications of the isohydric principle and "salt effects," etc., 

 will be studied in the future. 



TABLE 2 



(Curve E) 



TABLE 3 



{Curve D) 



CORRECTIONS FOR "SALT EFFECTS" 



The bacteriologist and botanist, as well as the chemist, are in- 

 terested in knowing the error in measurement of hydrogen ion 

 concentration caused by these "salt effects." It will be ob- 

 served that in the above curves the indicator is changed into the 

 deeply colored salt to the extent of from 8 to 30 per cent, which 

 covers the best range for accurate colorimetric work. As stated 

 above, the entire range will be given later. The percentage 

 change in hydrogen ion concentration necessary to produce the 

 same color intensity in the different concentrations of the phos- 

 phate solutions is practically independent of the color intensity 

 in this range. In other words, between about 8 and 30 per cent 

 change of the indicator into the colored salt, the deviation in P H 

 with changing phosphate concentration, but constant color inten- 

 sity is practically independent of the value (N — Na) /Na or per 

 cent of indicator present as colored salt. 



Another way of stating this is to say that for a given hydrogen 

 ion concentration more phosphate produces more color in the 

 solution or a greater positive "salt effect," while more sodium 

 produces less color. Now the magnitude of this "salt effect" is 



