7 Aa ge es ae a 
1912] BRIGGS & SHANTZ—WILTING COEFFICIENT 35 
It should be recognized clearly that the formulae which have 
been deduced will not necessarily give the correct calculated value 
of the wilting coefficient within the limits of the probable error of 
the ratio. The uncertainty regarding the value of the observed 
quantity (moisture equivalent, hygroscopic coefficient, etc.) enters 
into the calculation of the wilting coefficient for any particular soil, 
in addition to the uncertainty of the ratio. According to the 
formulae, a linear relation exists between the observed quantity 
and the wilting coefficient in each case, and the observed departures 
are attributed to accidental experimental errors. If this is true, 
then the probable error of the calculated wilting coefficient for a 
given soil can be made to approach the probable error of the ratio 
as a limit simply by increasing the accuracy and number of the 
determinations of the observed quantity. 
The probable error of a single determination of the wilting 
coeficients in our experiments is given below for each method, 
expressed in per cent of the wilting coefficient. 
Moisture equivalent method, +2.9 per cent 
ygroscopic coefficient method, + 7.1 per cent’ 
Moisture holding capacity method, +8.3 per cent 
Mechanical analysis method, + 10.0 per cent 
These errors are not to be applied to any other determinations, 
since they represent simply the degree of accuracy attained in our 
particular experiments. If the number of physical measurements 
made upon each soil had been increased, the error would have been 
reduced. 
FORMULAE SHOWING RELATIONSHIPS BETWEEN PHYSIOLOGICAL AND 
HYSICAL MEASUREMENTS OF MOISTURE RETENTIVITY 
For convenience in reference, the formulae for determining the 
wilting coefficient of a given soil by indirect methods are here 
presented in collected form, together with the probable error. 
moisture 2 Sautvalent 
1.8 007) 
Wiltika cociicient hyn ceeficent 
Wilting coefficient = 
moisture boldiag ae 21 
2.90(1+0.021) 
Wilting coefficient = 
o.o1 sands+o.12 silt+o0.57 clay 
Wilting coefficient = 
