70-72] LIME MANURES 2Q 



showing that chemical action has taken place, and the quick- 

 lime has combined with the water to form slaked lime. 



70. Solubility of Lime. — Although limestone (car- 

 bonate of lime) is not soluble in pure water, slaked lime 

 (hydrate of lime) is. Place a little powdered marble in a 

 test-tube, and in another place a little of the slaked lime 

 obtained in the last experiment. Add to each half a test- 

 tube full of water and shake up. Allow both to settle and 

 pour off the clear liquid into two other test-tubes. Filter 

 if necessary. To each of these two clear liquids add a few 

 drops of ammonium oxalate. The one in which the marble 

 has been shaken will remain clear, showing that none has 

 been dissolved ; whilst the other will give a white precipitate, 

 showing that some of the slaked lime has entered into 

 solution. 1 



71. Action of Air on Lime. — When lime is ex- 

 posed to the air it absorbs carbonic acid and is converted 

 into carbonate of lime, which is known as mild lime. Pour 

 a little lime-water (a solution of slaked lime in water) into 

 an evaporating-dish and leave it exposed to the ah' for an 

 hour or two. At the end of that time it will be covered 

 with a thin scum. This is because the lime in the solution 

 has been turned into carbonate of lime, which, being 

 insoluble in the water, forms a scum over the surface. 



72. Action of Lime on Acids.— Lime is not only 

 useful as a food for plants, but it improves the soil in many 

 other ways. One of these has already been pointed out in 

 paragraph 63. Another use of lime is to add it to * sour ' 

 soils, or soils which contain such quantities of acid that they 

 will not grow good crops. To show this action, one-third fill 



1 Distilled water is seldom perfectly free from carbon dioxide ; 

 hence a trace of the marble is often dissolved, giving a faint precipitate 

 with ammonium oxalate. When this is the case the student should 

 notice the great difference between the precipitate obtained after using 

 lime and that obtained by using marble. 



