i8 



TROPICAL AGRICULTURE 



CHAP. 



How to ex- 



amine soils 



mechanic- 

 ally ' 



Lime effer- 



chloric acid 



is poured 



on it. 



EXAMINATION OF SOILS. We have seen that soils are 

 classified according to the proportion of clay, sand, lime and 

 humus they contain, and the presence of these substances in 

 the soil may be very readily ascertained by the following 

 simple experiments : Weigh out a quarter of a pound of 



, , .. . , , -n i i i -i / 



the earth after it has been well dried, boil it for a short time 

 in a pint of water and then pour it into a glass vessel. A 

 piece of blue litmus paper should then be put in, and if the 

 paper turn to a red colour, it shows that acid humus is 

 present in the soil, and that lime is necessary to counteract 

 the acidity. More water is then to be added, the whole is 

 to be well stirred, and the muddy water is to be carefully 

 poured off into a large vessel, care being taken that none of 

 the sand which settles to the bottom is lost. The sand is 

 then to be stirred up with fresh water, which is again poured 

 off into the larger vessel. And this is to be done several 

 times until the sand becomes quite clean and free from mud. 

 The contents of the larger vessel are to be allowed to remain 

 for several horns until the fine mud settles to the bottom 

 when the clear water is to be carefully poured off. The 

 sand and the mud should then be dried and weighed 

 separately ; when, by comparing their weights with a quarter 

 of a pound, the proportion of sand and earthy matter in the soil 

 can be ascertained. To discover the presence of lime in a 

 so ^ ^ * s on V necessary to pour a little hydrochloric acid 

 U p O n it ; this will cause effervescence if there be any lime, 

 and the degree of the effervescence will give to an ex- 

 perienced observer a rough indication of the quantity of 

 lime. To ascertain the exact quantity of lime, however, the 

 acid must be allowed to remain some time on the soil, and 

 then a solution of ammonia must be added. All the lime 

 will, by this means, be dissolved out* of the soil and it will 

 remain in the liquid, from whence it can be thrown down by 

 a solution of carbonate of potash or oxalate of ammonia. 

 But this process can only be attempted by a person having 

 some knowledge of chemistry. The proportion of vegetable 



