2 74 Journal of A gricultural Research voi. xxi, No. 4 
Tabi^E IV .—Comparison of leaching with sodium sulphate and calcium sulphate, followed 
by water, showing the rate of percolation and the character of the percolate 
Leach¬ 
ing 
No. 
Leaching solution. 
Percolation 
rate per 
minute. 
Acid re¬ 
quired to 
neutralize 
100 cc. of 
percolate. 
Character of per¬ 
colate. 
I 
M\io Na 2 S 0 4 . 
Cc. 
3- 33 
Cc. 
3- 0 
Slightly turbid. 
2 
1. 92 
l- 7 
Clear. 
3 
.do. 
1. 02 
I- 5 
Do. 
4 
Water. 
. 62 
8-5 
Very turbid. 
5 
. 007 
8-5 
Do. 
1 
CaS 0 4 , Sat. Sol. 
2. 18 
3- 0 
Slightly turbid. 
2 
.do. 
1. 47 
1. 8 
Do. 
3 
1. 16 
1. 8 
Clear. 
4 
Water. 
i-43 
1. S 
Do. 
5 
2. 17 
4. 0 
Do. 
6 
1. 79 
2. 2 
Do. 
7 
i- 73 
!• 5 
Do. 
8 
' 1.56 
i- 5 
Do. 
Although the soil used in these experiments is almost impermeable to 
pure water it is easily leached with fairly strong ( M/io ) solutions of 
sodium chlorid or sodium sulphate. When these salt solutions are fol¬ 
lowed with water, however, the rate of percolation is at once greatly 
reduced and the percolate becomes turbid and alkaline. The same soil 
is also permeable to solutions of calcium chlorid and calcium sulphate 
and remains fairly permeable through the subsequent leachings with dis¬ 
tilled water. 
BASES OF IRRIGATION WATERS 
In respect to the reactions produced in the soil it is assumed that 
potassium reacts in much the same way that sodium does and that 
magnesium reacts like calcium. For purposes of comparing one stream 
or water supply with another it seems proper to take the sum of the 
calcium and the magnesium as one factor and the sum of the sodium 
and the potassium as the other factor in a proportion. For convenience 
we may designate the first factor calcium and the second factor sodium 
and the ratio between them the calcium-sodium ratio. 
The calcium-sodium ratio of the average of the analyses of 19 great 
rivers of the earth as given by Hilgard 1 is 84 to 16—that is, the sum of 
the calcium and the magnesium is to the sum of the sodium and potas¬ 
sium as 84 is to 16. According to the same authority the calcium- 
sodium ratio of the Nile is 69 to 31 for the high-water stage and 79 to 21 
for the low-water stage. It may be remarked that the calcium-sodium 
ratio of a stream is a much more constant factor at any given point than 
is the total salt content. 
For purposes of comparison with the ratios given above, data are 
assembled in Table V concerning 19 important irrigation streams in the 
1 Hilgard, E. W. soils ... p. 23. New York, London. 1906. 
