EXPERIMENT STATION BULLETINS. 835 



The explanation of this penomenon is self-evident. The Ag^SO^ reacts 

 with BaCK to form BaS04 and AgCl. Both of these salts being almost 

 insoluble cause a minimum depression when the reaction is complete. 

 Upon further addition of BaCL after the complete precipitation of 

 BaSO^ and AgCl, the lowering of the freezing point rises because the 

 BaCl2 remains in solution. 



So while it could be stated as a very general rule that if a soil contains 

 a free soluble acid or acid salt it will always give an acid curve when it 

 is titrated with Ca(0H)2 yet it is possible sometimes to obtain an acid 

 curve which is not due to an acid or acid salt. Such a case, however, will 

 probably be very rare. 



In the foregoing exposition an attempt has been made to indicate 

 briefly the underlying principles governing the freezing point method for 

 determining the nature of acidity and lime requirement of soils. It has 

 been seen that three distinct types of curves are obtained, and each one 

 of these curves signifies a definite phenomenon. Next a description of 

 the procedure involved in the method, the presentation of the detailed 

 results obtained, and the possible explanations therefor, are in order. 



DESCRIPTION OF THE METHOD AND PROCEDURE. 



For determining the nature of soil acidity and lime requirement of soils 

 by the freezing point method, the Beckmann apparatus was employed 

 with certain modifications. The complete set of apparatus used is 

 showTi in Figure 5. It is composed of a Beckmann thermometer A, a 

 glass tube B which contains the soil, a larger tube C which acts as an 

 air jacket, a. battery jar D which contains the cooling mixture, composed 

 of crushed ice and NaCl, and a wooden box E in which the battery jar 

 is placed and surrounded with poor heat conducting material to prevent 

 rapid radiation of the cooling system. The glass tube B is 1 inch in 

 diameter and 9 inches long, w^hile glass tube C is 1.5 inches in diameter 

 and 6 inches long. Vessels F and G act as accessories to the above main 

 apparatus. Vessel F contains a cooling mixture of the same or different 

 temperature as that in the battery jar D, and its cooling mixture serves 

 the purpose of taking off more rapidly the initial heat of the soil mass by 

 bringing the tube containing the soil mass into intimate contact with it. 

 Vessel G acts simply as a stand for the thermometer when it is taken out 

 of the glass tube B for preparing another soil sample or for adding 

 Ca(0'H)o to the soils at the end of each freezing point determination. 

 In this vessel there is a glass tube of the same dimensions as the glass 

 tube B. By cleaning this tube at the beginning of each experiment it 

 becomes unnecessary to clean the bulb of the thermometer every time the 

 latter is taken out of the soil tube to add Ca(OH)o to the soil. Near to 

 this set of apparatus are kept burettes attached to bottles of distilled 

 water and Ca(OH)„ stock solution, or to bottles containing any other 

 reagent employed. 



For determining the lime requirement of a soil the following procedure 

 was finally adopted: First the freezing point of pure distilled v/ater was 

 determined and this point was used as a standard for ascertaining the 



