724 STATE BOARD OF AGRICULTURE. 



rapidly. On the other hand, it mnst be stated that practically all soils 

 which show a small solubility product like these soils do were found to 

 give nearly always a high rate of solubility. 



SUMMARY. 



In tlie present bulletin there are presented the results of an investiga- 

 tion on the rate and extent of solubility of soils under different salt, 

 fertilizer, and acid treatments, at different moisture contents, and at 

 various temperatures; also of different types of untreated soil contain- 

 ing various quantities of organic matter and different degrees of fineness 

 of particles. 



The method employed in measuring the rate and extent of solubility 

 of soils was the freezing point method. The method proved ideal for 

 the purpose. 



The general procedure of the investigation consisted of washing the 

 treated or untreated soils with distilled water until all their free soluble 

 substances were eliminated and their freezing point depression was 

 very close to that of distilled water. For determining the rate and ex- 

 tent of solubility at the high moisture content the washed soils were 

 placed in glass freezing point tubes, the proper amount of water being 

 added, and their freezing point depression was determined very often 

 for a long time. For determining the rate and extent of solubility at 

 low moisture content the washed soils were placed in glass tumblers, 

 after they had reached the optimum moisture content, placed outdoors 

 under natural conditions, and their freezing point depression was de- 

 termined at certain set intervals. 



There were three different water contents employed, an optimum, a 

 ratio of 1 of soil to .7 water, and a ratio of 1 of soil to 5 of water. 



There were also three different temperatures used, below freezing, room 

 temperature and 53 °C. 



- When different classes of soil were treated with tenth normal salt 

 solutions of Ca(NO,)o, NaNO,, KNO,, KCL, ICSO,, (NH,),SO„ iVrgSO,, 

 KH0PO4, CaH4(P04)o and NaCH.^Og and then washed until all their 

 free soluble salts were eliminated and their water content consisted (»!' 

 1 of soil to .7 of water and kept at room temperature, it was found (1) 

 that the rate of solubility of all the salt treatments except (NHJ.SO, 

 was slow and gradual and the process continued for a long time even liM) 

 days, but usually for about 50 days. In the case of the (NH/lj^O^ 

 treatment the velocity was quite rapid at the beginning, but it soon 

 slowed down. At the end of about 00 days there was an apparent con- 

 stancy or equilibrium in the solubility. 



(2) The extent of solubility, or the amount of material that went 

 into solution when the apparent constancy was attained is very appre- 

 ciable in all the salt treatments and in all the soils, with few exceptions. 

 All the soils except sand, treated with NaNO,, KNO,, KCL, K,S(),, 

 (^114)2804, MgS04 and NaCaH^Oo yielded quite a large amount of 

 material to solution. Thus, the depression in many cases rose from 

 .005° to about .110 °C or from 125 to 2750 parts per million of solution. 

 The only salt treatments which did not cause a large solubility product 

 are the Ca(]S[0.^)2, KH3PO4 and CaHjr04),,. The depression in some 



