124 



SOILS AND FERTILIZERS 



is added to 250 c.c. of distilled water. The solution should be 



shaken well each time before using as the zinc sulfide is insoluble and 



tends to sink to the bottom of the vessel. 



The lead acetate paper is made by dipping strips of filter paper 



into a saturated solution of lead acetate and drying. 



Procedure. — Place in a 250 or 300 c.c. 

 Erlenmeyer flask a 10 gram sample (well 

 pulverized) of the soil to be tested. Now 

 add 5 c.c. of the calcium chlo ide-zinc sulfide 

 reagent, the former being in solution and 

 the latter in suspension. Add 75 c.c. of dis- 

 tilled water. Place on a wire gauze over a 

 flame and bring to boiling; Boil exactly one 

 minute, being careful not to allow the sample 

 to froth over. 



The boiling having become constant and 

 the C0 2 being driven off, lay over the mouth 

 of the flask a strip of lead acetate paper 

 moistened in distilled water. Allow it to 

 remain there exactly three minutes. The test 

 is now complete and acidity is indicated by 

 the blackening of the paper. 



Exercise VII. — Incrustation of " al- 

 kali " by capillary action. 



Materials. — Sandy loam, lamp chimney, 

 pan, salt. 



Procedure. — Prepare a lamp chimney by 

 neatly tying over the end two thicknesses of 

 cheesecloth. Fill with sandy loam. Set the 

 chimney now prepared into a solution of common salt. The salt 

 solution will soon rise through the column by capillary action and 

 evaporation will take place f om the soil. This will soon cause 

 an incrustation of " white alkali " on the surface of the soil 



Explain this experiment in relation to irrigation practice and 

 moisture conservation under arid conditions. 



Fig. 22. — Apparatus 

 for the zinc sulfide test 

 for soil acidity, (a) lead 

 acetate paper in posi- 

 tion, (6) flask, (c) soil 

 treated with calcium 

 chloride and zinc sulfide, 

 (d) tripod, (e) Bunsen 

 burner. 



