^SOILS 1 T 



poured oft". The s:ind and the mud should then be dried and 

 weighed separately, when, by comparing their bulk or weight, 

 the proportion of sand and earthy matter in the soil can be 

 ascertained. 



To discover the presence or absence of lime in a soil. Besides 

 the blue litmus paper test for lime, as described above, the 

 presence of lime may be ascertained thus: Take some 10 or 

 20 small samples from different parts of the ground, mix them 

 well together, then place a small sample in a tumbler and pour on 

 it a wine-glassful of muriatic (hydrochloric) acid. If the liquid 

 tizz and bubble freely, the soil may be considered to contain a 

 sufficiency of chalk ; but if it only effervesces feebly, it is safe to 

 conclude that a dressing of lime is desirable. 



To ascertain proportion of humus in the soil. Heat for an 

 hour to a red-heat, a given quantity of thoroughly dry earth 

 in an iron or clay vessel ; the soil rapidly blackens if much humns 

 is present, and then turns red or yellow r , the vegetable matter 

 being burnt off ; when cool, weigh the earth, and the loss in. 

 weight will give the proportion of humus in the soil. 



The capacity of soils for holding moisture. This power of 

 soils is mainly dependent on the mechanical texture or porosity 

 of the soil material. In a soil consisting of solid particles of fairly 

 uniform size, the interspaces are about 40 per cent, of the volume, 

 whether the particles are large or small ; but if the particles are a 

 mixture of large and small (as gravel and sand), the volume of the 

 interspaces is much diminished. On the other hand, if the par- 

 ticles themselves are porous, as in the case of chalk, loam, and 

 especially humus, the volume of the interspaces is much increased. 

 It is this volume of the interspaces that determines the amount of 

 water which a soil will hold when perfectly saturated, or the 

 amount of air which it will contain when dry. The influence of 

 humus on the capacity of a soil for holding moisture is remarkable. 

 SCHUBLER found that after 72 hours exposure to moist air, humus 

 had taken up nearly 2\ times as much water as clay, and 40 times 

 more than sand, which, under the same circumstances, took up 

 16 times less than clay. A simple way of ascertaining the power 

 of any soil to hold water is given thus: Fill a flower- pot nearly to 

 the top with dry soil, and then weigh it ( the weight of the poU 

 both wet and dry, must, of course, be known). Then gradually 

 pour water on the soil until it begins to drop from the bottom. 



