METHODS OF MECHANICAL ANALYSIS 7 



natural division between them, what is called clay consisting 

 for the most part of extremely fine sand. Any separation 

 into sand and clay is thus purely arbitrary, and the results 

 obtained depend entirely on the method adopted. Moreover 

 analysts have never agreed on any definition of sand and 

 clay, nor have they adopted one general method for their 

 estimation. The results arrived at by the older methods of 

 separation have thus no definite value, while they at the 

 same time afford no true representation of the constitution of 

 the soil analysed. 



The aim of the mechanical analysis of a soil is to determine 

 the proportion of its different physical constituents. Its 

 scope is generally limited to determining the proportion of 

 particles of different sizes ; but in some schemes this scope is 

 enlarged to include a determination of the calcium carbonate 

 and humus in each group of particles. As the particles which 

 make up a soil have an almost infinite variety of size, all 

 that can be done is to group them, by placing all that lie 

 between two dimensions in one group. We thus naturally 

 find both simple and more elaborate plans of analysis, in 

 which the constituents are arranged in few or in many 

 groups, the latter of course giving a more accurate view of 

 the constitution of the soil. The names commonly given to 

 these various groups as Stones, Gravel, Grit, Coarse Sand, 

 Fine Sand, Silt, Clay are very indefinite, and refer to particles 

 of very different size in different schemes of analysis. The 

 statement that a soil contains so much fine sand, or so much 

 clay, is thus of very little value, unless the mode of analysis 

 is also mentioned. On the other hand the physical characters 

 of a group of particles their diameter, or hydraulic value 

 are perfectly definite, and are much to be preferred for 



