Ill SOILS 19 



matter or humus, in the soil, is ascertained in a rough Organic 

 manner, by heating for an hour to a red heat, a given ^^oycd by 

 quantity of thoroughly dry earth in an iron or clay vessel, ^^^'^• 

 when the vegetable matter will be burnt off. The earth is 

 then to be cooled and weighed, and the loss in weight will 

 give the proportion of humus in the soil. 



Heavy and Light Soils.— It has been shown in the 

 mechanical examination of soils that the sand, which is the 

 heaviest part, falls to the bottom of the vessel when stirred 

 up with water, and that the clay being lighter is suspended 

 in the water for a time and can be poured off so as to leave 

 the sand by itself. This shows that sandy soils are heavier 

 than clay ones — indeed, a cubic foot of sand will weigh from 

 30 to 35 pounds more than the same quantity of clay. But 

 agriculturists call a clay soil a heavy one, and a sandy soil 

 a light one. These terms, however, refer, — not to the 

 relative weights, but to the facility with which the soils are 

 worked. The clay being tenacious or sticky, it is much Clay soil 

 more difficult to plough or to dig than a sandy soil, in which work" 

 the particles of sand move more easily one on the other and 

 allow the implements to pass freely through the' land. 

 Sometimes these soils are called stiff and free, instead of 

 heavy and light, and these are perhaps better names, for the 

 reason that they are not likely to confuse any one. Clay 

 soils retain much more moisture than sandy soils, as is well Clay soils 

 known, and this causes a great difference in regard to their motsture. 

 temperature. Clay soils are therefore spoken of as cold, and 

 sandy ones as warm, but a well-drained clay soil may be 

 warmer than an undrained, low-lying, sandy soil, and this 

 indicates the necessity for proper drainage of land ; for, as 

 will be shown later on, a certain degree of warmth is 

 requisite for the propagation of plant life. 



The Power of holding Moisture is possessed in a Retention 

 greater or less degree by all soils. If the end of a strip of f'ng'Jf^'^ 

 blotting paper be dipped into water, the water will run up 



C 2 



