EFFECT OF DRYING SOILS ON WATER-SOLUBLE CONSTITUENTS 



205 



with 87.9 and 81.8 which are the corresponding figures for the more con- 

 centrated solution. Thus it is seen that the recovery from the oven-dry 

 quartz was less in both cases, less by 5.6 per cent for the dilute solution and 

 by 6.1 per cent for the more concentrated solution. This relationship holds 

 throughout the second extraction also. This seems to indicate a real loss of 

 nitrate due to heating in the oven for 8 hours at 105°C. 



In order to test this point further, eight 10-cc. samples of a nitrate solution 

 containing 100 parts per million and eight 5-cc. portions containing 500 

 parts per milhon were treated with a few drops of saturated sodium carbonate 

 solution and evaporated to dryness on the water-bath. The nitrates in tour 

 samples of each were determined at once in the usual manner. The remaining 

 four samples of each concentration were dried in the oven at about 105°C. 

 for 8 and 21 hours, respectively. The results of all the determinations are 

 given in table 11. 



TABLE 11 

 Efect of heating at 105°C. on quantity of nitra'e recovered from quartz sand 



* Average of five readings, others average of four readings. 



Since all of the above were compared with the same standard and all samples 

 of each concentration were diluted to the same extent, the average colorimeter 

 readings bear to each other exactly the same relationship as would the actual 

 milligrams of nitrate, so the reading of unheated samples is considered 100 and 

 the other found thus: 44.59 : 40.31 = 100 : x. Of the weaker solution, 10 cc. 

 was diluted to 1000 cc. and of the stronger, 5 cc, to 2500 cc. in order to bring 

 each to approximately 1 part per million for reading. From these figures 

 the total milligrams of nitrate in each can be calculated. These figures show 

 a loss of nearly 10 per cent of the nitrate after the period of heating at slightly 

 above the boiling point. This is in accord with the earlier work recorded in 

 this paper. For this reason further discussion here will deal with the unheated 

 materials only. 



In the case of the coarse and medium grades with the same quantity of 

 nitrate added, the medium holds more, or gives up less, nitrate at both 



SOIL SCIENCE, VOL. XIII, NO. 3 



