78 



PHYSIOLOGY OF NUTRITION. 



stream of water. The residue on the sieve (skeleton) we dry and 

 weigh. We may further subdivide the skeleton into writing 

 sand (Streusand), fine gravel (Feinkies), medium gravel, and coarse 

 gravel. This is likewise effected by means of sieves. If we work 

 with Knop's series of sieves, the term coarse gravel is applied to 

 the residue left on a sieve with meshes 4'2 mm. wide ; medium 

 gravel to that left in a sieve with 2'7 mm. meshes, and fine gravel 

 to that left in a sieve of 0'9 mm. meshes. 



The fine earth is divided by washing into fine sand and clayey 

 constituents. The apparatus required is Kiihne's washing cylinder 



(Fig. 24). The glass cylinder 

 is 28 cm. in height, and 8'5 cm. 

 in diameter (both inside measure- 

 ments). At a distance of 5 cm. 

 from the base of the cylinder is 

 a tubulure which can be closed 

 in the manner indicated in the 

 figure. We place in the cylinder 

 30 gr. of fine earth which has 

 previously been heated for some 

 time with water, fill the cylinder 

 with water up to the level of 

 a mark towards the top, stir 

 with a rod, and then let stand 

 for ten minutes. The turbid 

 fluid is now run off, and we 

 pour a fresh quantity of water 

 into the cylinder, stir up, and 

 after five minutes again remove 

 the fluid. We proceed in this 

 way until all the clayey part 

 appears to be washed away, then dry the residue (fine sand) 

 which remains behind in the cylinder, and determine its weight. 1 

 The fine earth consists, as such analyses among other things 

 teach, of granules of very different sizes, a fact of which we may 

 at once satisfy ourselves by mounting some of the fine earth 

 in water on a slide, and submitting it to microscopic examina- 

 tion. The washing cylinder mentioned, and also sieves, are to be 

 obtained of Muencke, in Berlin. 



FIG. 24. Washing cylinder. 



1 A full discussion of the function of the .fine earth and skeleton, and of the 



