252 Retort of the Department of Chemistry of the 



It appears that there is no fixed relation between the dry matter 

 and the mineral elements of a plant, but that the use of these 

 elements for a unit of growth is within a certain limit pro- 

 portional to the available supply. This point is more fully dealt 

 with in experiments that will be described later. 



THE FERTILIZING VALUE OF AN IRON ORE WASTE. 



During the year 1908, there was called to the attention of 

 the writer a by-product, which is designated here as Iron Ore 

 Waste, supposed to be valuable because of the presence of a con- 

 siderable percentage of phosphoric acid. This phosphoric acid 

 is doubtless in combination as apatite, although no mineralogical 

 examination was possible by us because the material was sent to 

 us in a finely ground condition. As this seemed to be a matter of 

 considerable economic importance and as no experiments seemed 

 to have been made with this by-product, tests of its availability, as 

 compared with other phosphates, were made in one of the forcing 

 houses of the Station. The following table gives the results of 

 this experimental work. The artificial soil used was similar to 

 that given on pages 22 and 23 of this bulletin. The experimental 

 crop was barley. 



Table XIV. — Test of the Comparative Availability to Barley of the 

 Phosphoric Acid Contained in Iron Ore Waste. 



* Method adopted by the Association of Official Agricultural Chemists. 



