234, THE FARMER OF TO-MORROW 



Potomac River water, which was found to con- 

 tain only 7 parts of potash. Johnson tells of 

 an experiment with well water which contained 

 but 1% parts per ten million of phosphoric 

 acid, and notes that this solution gave twice 

 as much grain as a solution from field soil. 



In actual field tests in the growing of crops 

 there is no room for wonder that plants thrive 

 when their nutrients are supplied at so slow 

 a rate. The roots are constantly extracting the 

 soluble minerals from the solution and re-solu- 

 tion is going on continually. This has sug- 

 gested the query to many investigators of how 

 dilute a solution may be before plants lose the 

 power of feeding from it. There are certain 

 plants which extract iodine from sea water and 

 store in it their tissues in sufficient quantities 

 to make its extraction profitable in a com- 

 mercial way. Starch added to a solution is a 

 delicate test for the presence of iodine, so deli- 

 cate indeed as to give positive results with one 

 part in 300,000. But the amount of iodine in 

 sea water is so small that it does not respond 

 to the starch test. In an experiment, sea 

 water was evaporated to one one-hundredth of 

 its former bulk that is, the solution was con- 

 centrated one hundred times. Still the chemist 



