Mar. i. 1924 
Movement of Water in Irrigated Soils 
647 
in the combining or reacting values of the constituents. Such a method 
has been proposed by Stabler (77, 18) and elaborated by Palmer (jj) 
and has been extensively used by water analysts in connection with 
industrial problems though it has not as yet been used generally in 
connection with irrigation and drainage investigations. This method of 
interpreting water analyses is based on the use of what is known as the 
reaction coefficient for which the symbol r is used. The reaction coefficient 
"valence 
of an element or ion is determined by the ratio —7-=-• These 
J atomic weight 
coefficients for the more important radicals found in irrigation waters are 
given in Table XIV. 
Table XIV.— Reaction coefficients for the more important radicals found in irrigation 
waters 
Positive radicals. 
Reaction 
coefficients. 
Negative radicals. 
Reaction 
coefficients. 
Calcium (Ca). 
O. 0499 
. 0822 
Carbonate (C0 3 ) 
o- 0333 
.0164 
. 0282 
Magnesium (Mg). 
Bicarbonate (HC 0 3 ). 
Sodium (Na). 
•0435 
.0256 
Chlorin (Cl). 
Potassium (K). 
Sulphate (S 0 4 ). 
. 0208 
Nitrate (N 0 3 ). 
. 0161 
The reacting values of the dissolved constituents are determined by 
multiplying the parts per million by the reaction coefficient and the 
results obtained are designated by prefixing the symbol r to the symbol 
for the radical. Thus r Ca is the designation for the reacting value of 
calcium. The application of the method of reacting values to the state¬ 
ment of water analyses is illustrated in Table XV in which it is used with 
the results given in Table XII. 
The reacting values of the various constituents as given in the table 
are stated in terms of molecular equivalent units. If the analyses were 
complete and correct the sum of the reacting values of the bases or 
positive radicals should equal the sum of the acids or negative radicals. 
In ordinary analytical work the alkaline bases, sodium and potassium, 
are not usually determined. In the absence of this determination it is 
not possible to compute directly the proportions of the earthy bases, 
calcium and magnesium, to the alkaline bases or the percentage of the 
earthy bases to the total bases. This is a relationship that appears to be 
important in view of the known differences in the reactions of the 
elements of these two groups. 
In order to make an estimate of the percentage of the earthy bases to 
the total bases in the solution as well as to be able to make direct com¬ 
parisons between different waters it is convenient to compute the reacting 
values of the constituents into percentages. If it may be assumed 
that the determinations of the acid constituents are approximately 
accurate, the sum of the reacting values of the acids may be used as a 
basis for computing the percentages of the constituents. The results 
of such computation are given in Table XVI. It is believed that this 
method of statement of the results of analyses gives a fairly clear picture 
of the essential features of the solution and also permits a fair comparison 
of one solution with another. 
