MANUAL OF GENEEAL AGRICULTURE. 23 



utes. The lime will combine with"the sulphuric acid and 

 leave the phosphoric acid in solution. By merely testing 

 the solution with litmus paper does not prove the presence 

 of phosphoric acid, even if the blue does turn red, since 

 we have added sulphuric acid and some of this may not 

 have been removed by combining with the lime. Hence 

 we must use a special test for phosphoric acid. Filter and 

 to % of a test tube of the filtered liquid (nitrate) add 3 

 or 4 c.c. of nitric acid and heat until it just begins to boil. 

 Add !/4 test tube of ammonium molybdate. A yellowish 

 color proves the presence of phosphoric acid. 



As a control repeat the experiment, using 10 grams 

 of sand instead of 10 grams of bone. Upon the addition 

 of ammonium molybdate does the yellowish color appear? 



23. ALKALI SOILS. 



Materials: Three tomato cans, small pan, 3 evapo- 

 rating dishes, sodium carbonate, sodium chlorid, sodium 

 sulphate, hydrochloric acid. 



Among the injurious constituents of many soils of 

 arid regions are certain salts collectively known as "al- 

 kali. ' ' Whenever the rainfall is scant they are not leached 

 out of the soil as fast as formed and so accumulate. As 

 the rain water evaporates they are left on the surface, 

 where they form a white deposit known as "white alka- 

 li." However, there is also a black alkali formed by 

 another salt, sodium carbonate. This is the worst form of 

 all since it combines with the humus or organic matter of 

 the soil to form a black mass, and also corrodes the plant 

 just at the surface of the soil and kills it. Glauber's salt 

 or sodium sulphate, together with common salt or sodium 

 chlorid, and some others, form white alkali which is much 

 less injurious than "black alkali." 



Obtain enough soil to fill the cans and divide it into 

 three parts. Put one part into a can untreated. Put an- 

 other part into the pan. Add 15 grams of powdered sodium 

 carbonate and mix thoroughly, then transfer to another 

 can. To the last part add 5 grams each of sodium chlorid and 



