194 



The partial mechanical analysis outlined above thus separates every 

 soil sample thereby treated into the following grades: 



pebbles 

 > 3 mm. 



gravel 

 3 1 mm. 



Field sample 



true soil 

 < 3 mm. 



earth 

 < 1 mm. 



coarse sand 

 1 '5 mm. 



fine earth 

 < '5 rnm. 



Both the gravel retained by the 1 mm. sieve, No. 3, and the fine 

 earth which passed through sieve No. 4, have to undergo further differ- 

 entiation. The former by means of sieve No. 2 is separated into* 

 " coarse gravel " and " fine gravel," and from a fresh quantity of the " true 

 soil " 50 grammes in weight a sufficient amount of fine earth is obtained 

 by sifting (as the 250 grammes were sifted before) through sieve No. 4. 

 This new quantity of fine earth is now well stirred and washed, in a man- 

 ner similar to that already described, through sieve No. 5. To the residue 

 on this sieve the term " medium sand " is applied. The sifted product 

 obtained in this way is brought into sieve No. 6 and again carefully 

 washed : the name " fine sand " is given to what remains on the sieve. All 

 the products remaining on each of the sieves are weighed after drying at 

 105C. 



The fine grained mate-rial which has passed through sieve No. 6 is 

 placed in a syphon cylinder of the construction indicated in the annexed 

 sketch. The height of the cylinder is about 40 centimetres, and the in- 

 ternal diameter is six centimetres. This cylinder is marked near the neck, 

 and another mark is made at a level 200 millimetres below the first one. 

 When the sifted soil has been placed in the cylinder the latter 

 is filled with water to the upper mark, after which it is stoppered, in- 

 verted, and well shaken: it is then placed at rest in its normal 



