18 



SCIENCE 



[N. S. Vol. LI. No. 1305 



At present we may conclude that the speci- 

 fically protective effect of blood serum is due 

 not to the combination or inorganic constitu- 

 ents but to the proteid constituents of the 

 blood. This may perhaps explain the fact 

 that different blood sera may differ in their 

 beneficial effect. We even found that the 

 blood sera of diseased, anemic Liviuli may 

 become as ineffective or as injurious as sea- 

 water. Whether the action of microorgan- 

 isms enters as a factor in the case of blood 

 sera of anemic Limuli remains still to be 

 determined. 



Leo Loeb 



a preliminary note on soil acidity 



Whatever may be the cause and nature of 

 soil acidity, apparently part of this acidity is 

 due to some of the materials which constitute 

 the soil itself. This gives rise to the question 

 as to whether the minerals from which the 

 soils are derived are acid; and if not, what 

 changes occur in these minerals to make them 

 acid and what factors cause these changes. 

 Therefore in some work on soil acidity that 

 has recently been done in this laboratory, the 

 problem was attacked along a line somewhat 

 different from that usually followed. Instead 

 of working with acid soils entirely, neutral 

 and basic soils were also chosen and the one 

 factor which probably, more than any other, 

 has to do with the natural changes produced 

 in the soil forming minerals — namely, water 

 leaching through the soil — was investigated. 

 After workiiig with a few soils, it seemed 

 advisable to experiment with the more abun- 

 dant minerals which constitute certain types 

 of soils, and with a few of their decomposition 

 products. 



Such materials as the following were taken 

 for the experiments : soils, rocks, miscella- 

 neous gravel, pure minerals such as quartz, 

 hornblende, microcline and garnet, and some 

 of the decomposition products of the above 

 mentioned minerals and rocks such as silicic 

 acid, kaolin, silica, etc. ^Nearly all of the 

 rocks, gravel and pure minerals were found 

 to be either neutral or slightly basic. The 

 materials were leached with water containing 



carbon dioxide, and analyses were made to 

 determine what changes had occurred, both 

 in the samples and in the percolated water. 



The results from this work show that of all 

 the samples that were leached, no matter 

 whether the original material was basic or 

 acid, the resulting material was acid; and 

 that with the exception of the decomposition 

 products such as silicic acid, kaolin, etc., 

 nearly all of the samples became more acid. 

 The fact should be emphasized here that all 

 of the materials, with the exception of the 

 soils themselves, were minerals or rocks which 

 contained no organic matter. Hence the acid- 

 ity was not due to organic matter. 



From the above statements, the conclusion 

 may be drawn that the compounds formed 

 from some of the soil-forming minerals due to 

 leaching, are an important factor in making 

 soils acid. 



Having shown then that some of the mate- 

 rials of which soils are composed, on being 

 leached with water containing carbon dioxide, 

 make soils acid, the next logical step in this 

 research was to try to determine how these 

 compounds give rise to this acidity. 



This problem was attacked by determining 

 the hydrogen ion concentration of neutral 

 water extracts of the materials in question; 

 and by determining the hydrogen ion concen- 

 tration of similar extracts after different 

 known quantities of standard calcium hydrox- 

 ide had been added. A curve plotted from 

 the results of these determinations should 

 show (1) any excess of hydrogen ions in the 

 solution; (2) the presence of any compound 

 that is capable of taking up calcium hydroxide 

 as a result of adsorption, by the formation of 

 addition products, or by true chemical action; 

 and (3) any excess of free hydroxyl ions. To 

 illustrate, let the following figure represent 

 the relation between the hydrogen ion con- 

 centration (expressed as P;,) in a solution and 

 the amount of calcium hydroxide that has 

 been added. Then line ab shows a decreasing 

 excess of hydrogen ions in the solution; he 

 that the hydroxyl ions are being removed from 

 the field of action as fast as they are added; 

 and cd, an increasing excess of hydroxyl ions. 



