SIS STATE BOARD OP AGRICULTURE. 



metals aluiiiiniim, iron, calcium, potassium, sodium, and magnesiuui. 

 These silicates are salts of strong bases with weak acids, and being some- 

 what soluble in water are greatly hydrolyzed. Upon hydrolysis the acid 

 remains more or less in an insoluble form while the bases go readily into 

 solution. Now it is a well known fact that the strength of the bases and 

 acids has a very marked effect upon the indicators commonly employed 

 for determining the end point of neutralization. Thus, for example, 

 phenolphthalein cannot be used with weak acids or weak bases. If the 

 acid is so weak that its salts, even with strong bases, are hydrolyzed, 

 the free base begins to react with phenolphthalein long before enough 

 base has been added to completely neutralize the acid. The result is the 

 appearance of a faint color on the addition of a little alkali. In the 

 Veitch method phenolphthalein is employed as the indicator. Now it 

 is readily evident that if the soil contains soluble weak acids consisting 

 of silicic and organic acids, the alkali color begins to manifest itself long 

 before enough of the base is added to completely neutralize all the soluble 

 weak acids present. The result is that the soil shows a low lime re- 

 quirement and consequently its true maximum lime requirement will not 

 be known. 



As it will be subsequently shown, however, the acidity of the mineral 

 soils appears to he due almost entirely to the acid alumino-silicates, 

 silicic acid, and silica, and that the mineral soils rarely if ever contain 

 permanently free soluble acids. Consequently the above objection to 

 using phenolphthalein in the Veitch method is neither absolutely valid 

 nor so serious. The aforesaid objection, however, would hold true in the 

 hydrolysis of the minerals. As already stated these silicates or silico- 

 minerals upon hydrolysis yield soluble bases and more or less insoluble 

 acid. If the bases are present even in small quantities they will give a 

 neutral or alkaline reaction both to the phenolphthalein and litmus 

 paper, even if the silicates are far from being completely neutralized, 

 or satisfied with a base. This is due of course to the high ionization of 

 the bases and consequently to their strong reaction upon the indicator 

 as compared with the almost negligible ionization of the acid and there- 

 fore its extremely weak reaction upon the same indicators. It is very 

 possible to have a soil which would be neutral according to the Veitch 

 method and litmus paper test and yet this soil may possess a large 

 amount of negative or inactive acidity, as it is generally termed, i. e,, the 

 acid radical of the soil, which is composed almost entirely of alumino- 

 silicate, silica and silicic acid, is far from being entirely satisfied with 

 bases. 



A simple experiment, which apparently would seem to demonstrate the 

 validity of the above statements and at the same time help to make the 

 point in question more clear, may be cited as follows : If to 1 gram of 

 pure silicic acid is added 10 c. c. of distilled water and the mixture 

 stirred and a blue litmus paper is placed into it, the color of the litmus 

 paper will shortly turn decidedly red. If now to this mixture is added a 

 few drops of N/25 Ca(OH)o the red will shortly turn faint blue or neu- 

 tral and continue to remain faint blue or neutral. Yet this one 

 gram of silicic acid requires nearly 80 c. c. N/25 Ca(OH)o to 

 be fully satisfied before the Ca( 011)2 can remain in solution to 

 affect the concentration of the liquid phase, and therefore, also the 

 freezing point depression. In other words, the Ca(0H)2 added to the 

 silicic acid immediately combines with it to form calcium silicate and 



