June 10, 1921] 



SCIENCE 



539 



and wiry" or "tall and flabby" (p. 381) in 

 placing prosi)ective workers. What we have 

 to know is the limits of physical strength re- 

 quired for si)ecific jobs. Similarly the ques- 

 tion of heart efficiency as studied by Lowsley, 

 Crampton and Schneider in this country 

 would be of interest to the industrial phys- 

 ician. The omission of the nine figures 

 illustrating the application of iodine and 

 finger bandages (pp. 39 Y— 400) would provide 

 ample space for such a discussion. 



The maintenance of high production in any 

 field of activity depends upon the health of 

 the workers. Industrial hygiene need there- 

 fore make no appeal to the charity or human- 

 ity of industrial managers. It is primarily 

 good business. Efficient, healthy, productive 

 men and women have a social value whether 

 their production is for service or for profits. 

 Under any system of social organization in- 

 dustrial hygiene must therefore play a lead- 

 ing role in the future development of the 

 world's industry. 



Eeynold a. Spaeth 



School op Hygiene and Public Health, 

 Johns Hopkins University 



SPECIAL ARTICLES 



SOIL ACIDITY THE RESULTANT OF CHEMICAL 

 PHENOMENA 



Salts of strong acids with strong bases, of 

 strong acids with weak bases, of weak acids 

 with strong bases, of weak acids with weak 

 bases, calcium hydroxide, the lowering of the 

 freezing point, the catalysis of esters and the 

 hydrogen electrode are all in use in one or an- 

 other of the various methods advocated for 

 the determination of "soil acidity." The re- 

 sults obtained by the different methods show 

 that the condition of a soil at any time can be 

 considered as its progress towards a constantly 

 changing equilibrium according to the prin- 

 ciples of Le Chatelier. It is to be remem- 

 bered that those metallic elements occurring 

 in ordinary soil stand at the top of the elec- 

 tromotive series of elements and that sodium 

 and potassium compounds are all somewhat 

 soluble; whereas, many calcium and magne- 

 sium compounds and most iron and aluminum 



compounds are very sparingly soluble in 

 water. 



The entirely different results obtained with 

 different salts, and the large variations in soil 

 acidity recently found by Conner when soils 

 were kept at different moisture contents, make 

 it certain that acid soils usually contain many 

 soluble hydrolytic products which are con- 

 trolled in amount by the quantity of alkaline 

 earths and alkali metals present in the soil. 



Carbon dioxide gas has long been known to 

 cause many chemical changes in silicates and 

 phosphates resulting in the increased solubili- 

 ties of constituents making up these sub- 

 stances. The following results were obtained 

 in recent investigations where soils in culture 

 pots were treated with carbon dioxide. (The 

 details of the different experiments will be 

 published elsewhere.) 



1. An " alkaline " sandy soil became acid in 

 reaction in three months treatment with car- 

 bon dioxide gas. 



2. The acidity of an acid brown silt loam 

 was increased by treating the soil with carbon 

 dioxide gas. 



3. Liming this loam decreased its acidity 

 but not as much as the original " lime require- 

 ment" determination (Veitch) indicated. 

 One and one half times the total lime require- 

 ment did not neutralize the soil. 



4. Where the soil was limed, limed and 

 phosphated, and limed and treated with dried 

 blood or sodium nitrate, carbon dioxide gas 

 additions to the soil increased the soil acidity. 



5. The specific conductivity of extracts ob- 

 tained on treating the soils with conductivity 

 water showed that the carbon dioxide gas had 

 changed the constitution of the soil. The 

 specific conductivity of the carbon dioxide 

 treated soils was greater. 



6. The acidity of the soils was lowered by 

 extraction with conductivity water and the 

 lowering was greater for those samples which 

 had been subjected to the carbon dioxide 

 treatments. A further evidence that the acid- 

 ity was due to chemical changes in the soil 

 was that the aluminum and iron in the nor- 

 mal potassium nitrate extracts was effected by 

 the carbon dioxide treatments. 



