MANUAL OF GENEEAL AGRICULTURE. 25 



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24. GYPSUM TREATMENT FOR BLACK ALKALI. 



Materials : A tomato can, gypsum, sodium carbonate. 



Prepare a can of the same kind of soil as in the last 

 experiment. Weigh out 15 grams each of sodium carbonate 

 and gypsum (land plaster), powder each thoroughly and 

 mix them with the soil before placing it in the can, add wa- 

 ter to the soil slowly until it is saturated. Compact as in 

 the last experiment. Place in a warm place for two days 

 and note the incrustation. Is it "black alkali," or has the 

 gypsum changed it? How does the residue compare with 

 that in the third can in the last experiment? If the ma- 

 terials have been well mixed the sodium carbonate will 

 have . acted with the calcium sulphate ( gypsum ) and formed 

 insoluble calcium carbonate (limestone) and sodium sul- 

 phate one of the compounds in "white alkali." In this 

 manner the very harmful "black alkali" can be changed 

 to much less dangerous white variety. 



Besides containing harmful minerals, most alkali soils 

 are rich in soluble plant food such as nitrates and potas- 

 sium compounds. 



25. ACID SOILS AND HOW TO CORRECT THEM. 



An acid soil, litmus paper, evaporating dish, wood 

 ashes or slaked lime, pan. 



Not only do we have alkali soil, but to a limited ex- 

 tent in the West we have soils that are acid. They are 

 usually spoken of as sour soils. Some plants, notably 

 clover and alfalfa, will not thrive in such soils because 

 the soil bacteria are hindered by the acid present. 



Obtain some such soil or soils from tule land, poorly 

 drained clay soil, and soil from the school yard and test 

 as follows : Boil a sample a few minutes in a small quan- 

 tity of distilled water and allow the soil to settle. 



Place in the dish both kinds of litmus paper. Leave 

 the paper for several minutes as the soil may be nearly 

 neutral, i. e., neither acid or alkalin. Examine the lit- 

 mus and compare each with the original paper. 



Stir into a soil known to be alkalin a small handful 

 of slaked lime or wood ashes and test with litmus paper 



