19] 7 J Ayres: Nutrient Solution on Plants Grown in Sand Cultures 367 



500 c.c. had been used. The filter containing the sand was then 

 allowed to stand for about fifteen hours, and the sand was leached 

 with another 500 c.c. portion of water. The filtrate was evapor- 

 ated to dryness, the residue dehydrated at 100° C, and strongly 

 ignited in a platinum dish to destroy organic matter. The resi- 

 due was then dissolved in hot water and made up to definite 

 volume from which aliquot portions were taken for analysis. A 

 2000 g. sample of the washed sand used in the experiment gave 

 by this method the following analysis: 



N K P Mg Ca S 



00. 33.6 5.2 66.4 2.4 1.5.6 milligrams 



In this analysis, as well as in all the following analyses, the 

 statement made is for the total weight in milligrams of the 

 element contained in 2000 g. of sand, which was the quantity 

 contained in each pot. Table 4 gives a summary of the analysis 

 of each of the sixty samples of sand used. The total quantity 

 of each element present, calculated from the quantities of salts 

 added plus the quantity in the original sand, is given, as well as 

 the number of milligrams of the element missing from the pot at 

 the end of the growing season. This latter value is the difference 

 between the total weight of the elements present and the residue 

 as shown by the analysis of the water extract. The difference 

 thus obtained represents the quantity of the element absorbed 

 by the plant and adsorbed by the sand particles. It must be 

 admitted that it is not known just how great a factor adsorption 

 may be in the case of this sand. 



Discussion of Results 



In series I no nitrogen as nitrate remained in pots 1, 2, 3, and 

 4 of groups A, B, and C. In group D there is a small residue of 

 nitrogen in spite of the fact that the total crop production was 

 greatest in this gi"0up. The concentration of the solution clearly 

 affects the economical use of nitrogen, a fact which in general 

 is also indicated in series II and in series III. It is especially 

 noticeable that there is a much larger quantity of nitrogen left 

 in series III D than in either series I D or II D. The total crop 

 production for group III D was better than that of the D group 



