July 17, 1916 Influence of Calcium and Magnesium on Plant Growth 595 



Table; I. — Composition of materials supplying calcium and magnesium to the soil 



1 From Columbia, 111. 



The brown silt loam used in series C and D was taken from the surface 

 of sod land and had only the coarser roots removed. The calcareous 

 soil was taken from a layer varying from 8 to 12 inches in thickness and 

 72 inches below the surface in the forestry near plot 719 of the north 

 farm of the university. The coarser pebbles were removed before using. 

 The analysis in Table I refers to the portion used in growing crops; the 

 coarser pebbles show a higher content of calcium and magnesium, or 

 13.34 P er cen t oi calcium and 5.97 per cent of magnesium. 



The 6,000 gm. of sand, after being extracted with hydrocnloric acid, 

 contained for each pot from 768 to 852 mgm. of calcium and from 540 

 to 960 mgm. of magnesium. From the following tables it will be seen 

 that the plants had the power to obtain considerable quantities of the 

 apparently insoluble calcium and magnesium silicate, as they obtained 

 quantities in excess of the amount added in the seeds, although they 

 show lower contents than plants grown in an excess of these materials. 

 The chemically pure magnesium carbonate gave an immediate alkaline 

 reaction to phenolphthalein upon the addition of distilled water. Dolo- 

 mites Ci and C3 likewise showed an alkaline reaction to this indicator, 

 but only after having been in distilled water over night. Magnesite 

 after standing in distilled water from 8 to 12 hours was alkaline to 

 phenolphthalein, as was also the calcareous soil. 



In experimenting with artificially prepared magnesium carbonate, a 

 great deal of care was taken to obtain the alkali-free substance to begin 

 with. This can be prepared by a precipitation from solution with ammo- 

 nium carbonate. Magnesium carbonate in the presence of water has a 

 great tendency to hydrolyze, which may at least partially explain its 

 poisonous effect. 



