September 22, 1922] 



SCIENCE 



341 



sidered, or to those whicli are expansions and 

 continuations of them, for the student is thus 

 confirmed in his bad habit of being satisfied 

 with a statement from a text-book, rather than 

 encouraged to seek the real source, the journal 

 article. Another disadvantage arising from 

 this lack of references is the very real danger 

 that the reader will feel that at any point the 

 last word had been said on the subject, whereas 

 a glance at the original papers would show 

 him in truth that it was only the first. 



Since an international committee has already 

 established a notation for use in Physical 

 Chemistry, it would seem a pity that the 

 authors in this test have adhered to a local one, 

 for it will needlessly confuse the reader. 



The fact that this is the final revision of the 

 preliminary editions of 1917 and 1920 is assur- 

 ance that few if any misprints or errors are 

 likely to be found in the text. 



A list of the chapter headings given below 

 will show the general scope of the book : 

 Part I The atomic, molecular and ionic 

 theories and properties of substances 

 directly relating to these theories. 

 Tlie composition of substanees and 

 atomic theory. The molal properties 

 of gases and the molecular and kinetic 

 theories. The molal properties of 

 solutions and the molecular theory. 

 The atomic properties of solid sub- 

 stances. The electrolj'tie behavior of 

 solutions and the ionic theory. 

 Part II The rate and equilibrium of chemical 

 changes from mass-action and the 

 phase view points. The rate of chemi- 

 cal changes. 



The equilibrium of chemical changes 

 at constant temperature. Equilibrium 

 of chemical systems in relation to the 

 phases present. 

 Part III The energy effects attending chemical 

 changes, and the equilibrium of chemi- 

 cal changes in relation to these effects. 

 The production of heat by chemical 

 changes. The production of work by 

 isothermal chemical changes in rela- 

 tion to their equilibrium conditions. 

 The production of work from iso- 

 thermal changes by electrochemical 

 processes. The effect of temperature 

 on work producible by isothermal 

 chemical changes and on their equi- 



librium conditions. Systematization of 

 free-energy values. 



J. Livingston R. Morgan 



SPECIAL ARTICLES 



SAND DROWN, A CHLOROSIS OF TOBACCO 

 AND OTHER PLANTS RESULTING FROM 



MAGNESIUM DEFICIENCY 

 In connection with recent field investigations 

 in the improvement of tobacco production con- 

 ducted by the Bureau of Plant Industry in co- 

 operation with the North Carolina Department 

 of Agriculture attention was directed to a 

 characteristic chlorosis of the leaves of tobacco 

 plants on certain test plots. Investigation dis- 

 closed the fact that this disease often causes 

 serious damage to the tobacco crop on certain 

 types of soil, particularly in comparatively 

 wet seasons. The popular name of this chloro- 

 sis is "Sand Drown," a tei-m referring to the 

 fact that the disease is likely to occur in ag- 

 gravated form on the more sandy portions of 

 the field after heavy rainfall. As a result of 

 considerable field and laboratory study extend- 

 ing through several seasons this malady has 

 been found to be due to an insufficient supply 

 of magnesium in the soil or fertilizer. It has 

 been found, further, that the ratio between the 

 quantities of sulfur (sulfate) and magnesium 

 contained in the fertilizer is a factor of im- 

 portance, the symptoms of magnesium defi- 

 ciency being intensified by increase in the quan- 

 tity of sulfur applied to the soil. The details 

 of the investigations will eventually appear in 

 the Journal of Agricultural Research but be- 

 cause of considerable delay in publication re- 

 sulting from temporary suspension of this 

 journal it seems desirable to present at this 

 time a brief outline of the principal facts es- 

 tablished. The chlorosis in question usually 

 begins at the tip and along the outer margins 

 of the older leaves, advancing toward the leaf 

 base and extending progressively to the upper 

 leaves of the plant. In some eases, however, 

 the chlorosis involves large portions of the leaf 

 surface when first clearly recognizable. The 

 veins and midrib of the leaf tend to retain their 

 normal color. There is more or less complete 

 blanching of the leaf lamina, both yellow and 

 green chlorophyll pigments being affected 



