§ 97. SILT ANALYSIS. 1G9 



SILT ANALYSIS. 



97. This air-dried fine earth may be separated, still 

 further, into portions of different degrees of fineness by 

 a series of sieves, or, in a quicker and better manner, by 

 the process of silt analysis. 



a. To perform this with Kobel's apparatus (fig. 6), 

 weigh out 30 grms. of the air-dried soil, and boil it for a 

 long time with water, until the lumps are completely 

 broken up ; the operation may be facilitated by gentle 

 trituration with a small pestle ; in the case of very sandy 

 soils, it will be finished in half an hour, but for very 

 heavy clay soils, two or three hours may be required. 



When this is completed throw the whole mixture of 

 soil and water on a sieve with meshes 1 mm. wide, rinse 

 the residue on the sieve well with water, dry it at 100° C, 

 and weigh it ; that which passes through the sieve, and 

 the washings, are reserved for the silt analysis proper. 



The water reservoir of Nobel's apparatus should hold 

 about 10 litres, and the siphon tube that enters it should 

 extend down just far enough to allow 9 litres of vv^ater, 

 and no more, to flow out ; the other arm of the siphon 

 should be 60 cm. long, and should have just as large a 

 bore as the tube of the funnel with which it is connect- 

 ed. The relative capacities of the four silt funnels, Nos. 

 1, 2, 3, and 4, arc 1 : 8 : 26 : 64 ; together, they hold 5 

 litres ; the mouth of the largest funnel where the water 

 finally flows out of the apparatus should be provided 

 with a tube drawn out to a point, that is filed off until 

 the orifice is of such a size that, when all the funnels are 

 filled with water, and the connection with the reservoir 

 is made as above directed, 9 litres will flow through in 

 exactly 40 minutes. 



A large flask or beaker must be provided to receive 

 the water as it flows out of the largest funnel. 



The fine earth, that passed through the sieve with 

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