512 AGRICULTURAL ANALYSIS 



Proceeding in a systematic manner, attention may first be called 

 to the combination of potassium chlorid and magnesium chlorid, 

 that is to say, a combination of these metallic oxids with a com- 

 mon acid and then a combination of magnesium chlorid and mag- 

 nesium sulfate, that is a common base with different acids. If, 

 however, the problem be stated in a general form, potassium sul- 

 fate which has not yet been mentioned in this connection, must be 

 taken into account since this salt may be formed from the potas- 

 sium chlorid and magnesium sulfate already in the solution. This 

 gives a third combination of magnesium sulfate and potassium 

 sulfate, that is, a combination of the same acid with two metallic 

 bases and the last combination will be that of potassium sulfate 

 and potassium chlorid, the same metallic oxids with different acids. 

 In order to illustrate this problem graphically, van't Hoff gives 

 a table of the solubilities of these bodies, in convenient form. 



In mols. per looo mols. H.O 

 Saturation with K 2 C1 2 MgClj MgSO 4 K,SO 4 



A. Potassium chlorid 44 



E. Potassium chlorid and carnallit 5.5 72.5 .... 



F. Magnesium chlorid and carnallit i 105 



B. Magnesium chlorid 108 



G. Magnesium chlorid and MgSO 4 .6H 2 O 104 14 



H. MgSO 4 .7H 2 O and MgSO 4 .6H 2 O 73 15 



C. MgS0 4 . 7 H 2 55 



J. MgSO.7H 2 O and schonit 58.5 5.5 



K. Potassium sulfate and schonit 22 16 



D. Potassium sulfate 12 



L. Potassium sulfate and potassium chlorid 42 1.5 



The explanation of these diagrams is best given in van't 

 HofT's words: 



"The presentation of the whole of this material graphically 

 makes the understanding of it much easier. The rectangular axes 

 in the plane of the paper can be retained and from their point of 

 intersection at O (Fig. 45) the four single salts, potassium chlo- 

 rid, magnesium chlorid, magnesium sulfate and potassium sulfate, 

 can be laid off in the directions, A,B,C, and D, respectively. The 

 four combinations which they form, two by two, fall then within 

 the quadrants lying between the axes. We obtain in this way,. 

 a fashion of representing the facts something like Fig. 44 re- 



