June 26, 1916 Mineral Phosphates and Plant Nutriiioii 489 



available. He makes the statement that carbon dioxid was more active 

 than other acids in this respect. 



The degree of fineness plays an important part in the availability of 

 the crude phosphates. Jordan (11) proves this quite conclusively. 

 He procured better results from the phosphates which were ground to 

 an impalpable powder. Analysis of the plants showed an increase in 

 the proportion of dry matter to phosphorus as the size of the particles 

 decreased. Voelcker (29) in some of the earliest work says that the 

 efficiency of insoluble calcium phosphate depends upon the minuteness 

 of division; the finer the particles the more energetic will be its action. 



EXPERIMENTAL WORK 

 MEDIUM FOR PLANT GROWTH 



Pure white sand was. used throughout these experiments as a medium 

 for plant growth. For most of the work this material was leached with 

 a dilute solution of hydrochloric acid for three days to insure the removal 

 of plant food. The sand was then washed with distilled water until 

 there was no trace of acid in the drainage solution. Next it was placed 

 on clean paper until dry, when it was sifted, in order that foreign particles 

 might be removed. Samples were collected for a phosphorus determina- 

 tion from each lot of sand washed, but in no case during the progress of 

 the study was the slightest trace of phosphorus detected. 



POTS 



Two sizes of pots were used in this investigation. Wlien it was neces- 

 sary to grow the crop to maturity, the small glass battery jars, approxi- 

 mately 6 inches in diameter and 8 inches in height, proved very satis- 

 factory; but when a grain crop was desired, the 4-gallon stone pots were 

 more suitable. All jars were supplied with adequate drainage. 



For the cultures grown in the winter the pots were covered with a 

 coat of black paint, but for the summer series a white coat was placed 

 over the black. The black paint prevented the growth of algge and the 

 white had a tendency to keep the temperature from becoming excessive 

 within the jars. This precaution was clearly justified, for upon several 

 occasions there was a difference of 5° to 10° in temperature between the 

 black and white pots. 



KINDS OF CROPS GROWN 



Wheat, oats, rye, barley, timothy, cowpeas, soybeans, clover, and 

 alfalfa — nine common crops that are cultivated on Illinois farms — were 

 grown under various treatments for this investigation. High-grade 

 seed from the previous season's crop was selected for planting, and 

 in all cases the grains were treated with a solution of formalin to 

 prevent smut. 



