Dec. 2. 1918 Greensand as a Source of Potassium 489 



It is clear that potassium nitrate is able to supply something that gives 

 this salt an advantage clearly not derived from the potassium content 

 solely. It is probable that the nitrate ion contributed a favorable action 

 lacking to the other potassium salts used. 



As a practical means of meeting the potassium need this could hardly 

 be considered a practicable resource under present conditions. 



RESULTS WITH GREENSANDS AND GREENSAND MARLS 



A chemical study of the composition of greensand deposits shows a 

 wide variation not only in the materials present but likewise presents 

 almost every possible combination in proportions present. While potas- 

 sium, silica, and iron are ever-present constituents of glauconite, with it 

 are oftentimes found sulphates and phosphates, the latter sometimes in 

 considerable quantity. Calcium, usually present, is, of course, a major 

 constituent in the marl types. 



It is obviously difficult to get a strict basis of comparison between these 

 complex mixtures of slowly-soluble materials and the readily-soluble 

 pure salts above reported. It was hoped, however, that this might be 

 done by supplying in the culture solutions with which the pots contain- 

 ing these sand and marl mixtures were watered sufficient phosphates 

 and sulphates to supply the necessary demand of the rather sparse 

 plantings made in the pots. Such necessary constituents present in 

 quantities sure to be sufficient to satisfy the demands of the plants would 

 tend to reduce or efface the influence of additional quantities of these 

 substances added in the marls. The only required constituent not pres- 

 ent in the basic culture solution would be potassium, which would of 

 necessity be drawn by the plants from the marls or greensand, if they 

 were to get them anywhere. 



After deposits from several regions, chiefly from Virginia and New 

 Jersey, had been collected and analyzed, certain typical deposits from 

 both States were selected for use in these experiments. Two samples 

 called "greensand," because of the low lime content were selected, one 

 from each State. Two samples of "greensand marl," containing from 

 7.45 to 12.50 per cent of calcium oxid were also used, one from New 

 Jersey and a mixture of equal parts of two from Virginia. All are low 

 in phosphates and sulphates and vary widely in their potassium content. 



In making up the cultures in the manner already described, the quan- 

 tities of marl taken cover the rates of application customary in the days 

 of "marling." The potassium present was calculated, not on the more 

 readily available portion extracted with dilute hydrochloric acid but 

 on the total potassium present, determined by the hydrofluoric- acid 

 method.^ 



• Hicks, William B., and Bailev. Reginald K. methods of analysis of greensand. In U. S. Geol. 

 Survey Bui. 660-B, p. 53. 1917. 



