Mar. i, 1924 
Movement of Water in Irrigated Soils 
685 
to approach the subject of the alkaline carbonates in their relation to the 
soil from the basic rather than from the acid side. In such an approach 
it becomes possible not only to avoid circumlocutions of language but 
also to see more clearly into the heart of the problem. 
In dealing with the subject of alkaline carbonates in the soil solution it 
should be kept in mind that by the ordinary method of identification it is 
not the carbonate but the basic hydroxid that is actually determined (see 
p. 642). The method of titration gives not the quantity of C0 3 ions in 
solution but the quantity of basic ions that are in the solution in excess 
of the quantity of strong acid ions present. Thus, if one takes 50 cc. of 
N/10 NaOH to titrate with N/10 acid, it will require 50 cc. of the acid to 
complete the titration whether the solution is kept free from C0 2 or is 
saturated with it. In the same way with a soil solution, the quantity of 
acid that is required to complete the titration with methyl orange is the 
measure of the quantity of basic ions in the solution in excess of the 
quantity of ions of the strong acid radicals, such as chlorin, sulphate, 
or nitrate. The solution may contain much or little C 0 2 ; it will have no 
effect on the quantity of acid required. The quantity of C0 2 in the 
solution does influence the reaction of the solution with respect to the 
indicators. Thus solution of NaOH in water free from C 0 2 shows a pink 
color with phenolphthalein until the titration is completed. The addition 
of C 0 2 to the same solution of NaOH reduces the quantity of acid re¬ 
quired to titrate out the pink color of the phenolphthalein but not the 
quantity required to complete the titration with methyl orange. 
In reporting the analysis of a soil solution it would be quite as correct 
and possibly less confusing to state the result of the acid titration in 
terms of excess of bases to strong acids as to give it in terms of C 0 3 and 
HC 0 3 . This is, in fact, the custom of some analysts. It is not a matter 
of great importance what designation is used in reporting analytical 
results, but it is important to understand as clearly as possible what these 
designations mean. If it is clearly understood that the term carbonate, 
as used in connection with the soil solution, means the excess of bases 
over strong acids, there can be no valid argument against its use. There 
is, however, the possibility of misconception on the part of persons not 
thoroughly acquainted with the literature of the subject and the analyti¬ 
cal methods used. Such persons might infer that the term carbonate 
implied carbon dioxid in solution. 
The soil solution always contains carbon dioxid. This gas in the solution 
plays a most important r 61 e not only in the reactions between the solution 
and the soil but also in the reactions between the soil solution and the 
plants. It has been remarked above that calcium carbonate is practically 
insoluble in water that is free from carbon dioxid, but is very appreciably 
soluble in water containing that gas. There is ample evidence that the 
solubility of other soil materials also is influenced by carbon dioxid. An 
experiment recently conducted for the writer by J. F. Breazeale may be 
cited as an illustration. In this experiment two samples of the same soil 
were placed in large bottles and treated with water at the ratio of 10 
parts of water to 1 part of soil. The mixture was shaken thoroughly and 
one sample was saturated with carbon dioxid, the other not being treated. 
Each day the supply of carbon dioxid was renewed in the treated mixture. 
After five days the solution was filtered off and titrated with acid and 
tested for calcium. The results of these tests are given in Table XXVIII, 
expressed in reacting values. That is, the reacting value of the acid re¬ 
quired for titration is shown in the first column, and the reacting value 
