193 



needs to be ascertained here is, first of all, what the mechanical condition 

 of the soil is in localities where these crops do well, and next, how much 

 moisture such soils are capable of retaining under the climatic conditions 

 prevailing in this country. It was to give a start to research along these 

 lines that the investigations recorded on the subsequent pages were 

 initiated. 



METHOD OF MECHANICAL ANALYSIS OF SOIL. 



The complete sifting process used in the Government Analytical Labo- 

 ratory for these investigations included the employment of the following 

 sieves : * 



1. A brass-bottomed sieve with circular perforations 3 mm. in 



diameter. 



2. A similar sieve with perforations 2 mm. in diameter. 



3. Another similar sieve having perforations 1 mm. in diameter. 



4. A Kahl's (Hamburg) " Messingdrahtsieb No. 50." 



Lateral measurement of meshes '35 mm. '39 mm. 



Diagonal measurement of meshes '45 mm. '50 ,, 



5. A Kahl's (Hamburg) "Messingdrahtsieb No. 100." 



Lateral measurement of meshes '14 "17 mm. 



Diagonal measurement of meshes '22 '24 mm. 



6. An Ehrhardt & Metzger's (Darmstadt) " Florsieb No. 16." 



Lateral measurement of meshes '09 mm. 



Diagonal measurement of meshes '11 mm. 



For the mechanical analysis of soils all the above sieves are used, and 

 the sifting process is further supplemented by sedimentation in water. 

 When a chemical analysis is the chief object, sieves Nos. 1, 3, and 4* only 

 are employed, according to the method already described. 



In carrying out the mechanical analysis of a soil, a weighed average 

 quantity (generally from five to eight pounds) of the field sample is taken 

 and dry sifted through sieve No. 1. The pebbles left on the sieve are 

 washed and dried, and their weight noted for ultimate calculation in per- 

 centage of the water-free field sample. All that passes through sieve No. 

 1 is denominated " true soil." 



250 grammes of this true soil are placed in a porcelain dish; about 

 half a litre of distilled water is poured on, and the dish is allowed to digest 

 on a water-bath for at least two hours, the contents being frequently 

 stirred. When the soil has been so softened that it can be washed through 

 the sieves by the aid of a small brush, the actual sifting operation is pro- 

 ceed with as follows 1 : 



Sieve No. 4 is held over a dish containing distilled water; the moist- 

 ened sioil is placed in the sieve, and the latter is immersed with its per- 

 forated bottom about one inch or more below the water level in the dish. 

 By means of a small brush the soil is now stirred until particles no longer 

 pass through, after which the residue in the sieve is washed with distilled 

 water. This residue is next washed on to and through sieve No. 3. That 

 which passes through the latter sieve is dried and weighed as " coarse 

 sand," while the term " gravel " using the word as conveying the idea 

 of dimension and not that of nature is assigned to the residue upon thia 

 sieve. 



* Sieve Xo. 4 is no\v definitely replaced by a brass bottomed sieve with circular per- 

 forations mm. in diameter. 



N 



