V. THE ANALYSIS AND COMPOSITION OF SOILS 83 



over it. The surface of the prism is freed from vegetation, the box is 

 inverted over it, and by means of the spade, the box with the column 

 of soil is removed, a label giving particulars of the sample put in, and 

 the lid screwed on. A sample of the soil and sub-soil in situ is thus 

 obtained which can be further treated in the laboratory. Several of 

 such samples can be united before a final sample is taken. 



(3) A quicker and in many ways a satisfactory method of sampling 

 consists in taking specimens by means of a 2 or 2-| in. auger, the 

 borings being placed on a board, a number of them (a dozen or more) 

 from various parts of the area to be examined being mixed together 

 and taken for analysis. A board about 2 ft. 6 in. x 1 ft. 2 in., with a hole 

 in it just large enough to easily pass the auger, will be found conven- 

 ient to stand upon and also to receive the borings. 



For general purposes a chemical analysis of the soil is all that 

 is usually done, but great importance is undoubtedly to* be attached 

 to its physical properties (e.g., specific gravity, real and apparent, 

 specific heat, conductivity for heat, absorptive power for salts and for 

 water, size of particles, capillarity), and in America and Germany soils 

 are examined with a view to determining these properties and express- 

 ing them quantitatively ; but for methods the student is referred to the 

 writings of Knop, Koenig, Warington, Hall and Wiley. It is usual to 

 submit the soil to a rough mechanical analysis before commencing the 

 chemical analysis. 



Mechanical Analysis. The soil collected in its damp state is first 

 air-dried. This is done by spreading it on paper and exposing to air 

 for some days, care being taken to exclude dust, products of combus- 

 tion or other foreign matters. In order to increase the rate of drying, 

 the author has used a glass chamber provided with shelves, from which 

 air is drawn by a fan, driven by an electric motor, the necessary supply 

 of fresh air being admitted at the bottom, after being warmed by pass- 

 ing over resistance coils (used for diminishing the current supplied to 

 the motor) and filtered through calico. In this way air at a tempera- 

 ture of 25ito 30 C. is drawn over the soil, and drying is completed in 

 a short time. Before the soil is thoroughly dry it is rubbed between 

 the hands or with a wooden or rubber-covered pestle, in order to 

 crumble it to powder, care being taken not to crush stones or mineral 

 fragments. When dry, a convenient quantity, 1 or 2 kilograms, is 

 weighed out and passed through a sieve having meshes of 3 millimetres, 

 or 1 in. diameter (best made of metal with circular perforations). The 

 portion failing to pass this is subjected again to hand rubbing until no 

 aggregations of clay, etc., are left. Finally, the stones retained by the 

 3 millimetre sieve are removed and weighed, whilst the portion passing 

 through is stored in a stoppered bottle for the chemical analysis and 

 duly labelled, the percentage of stones removed being conveniently re- 

 corded on the label. 



It is rarely desirable to make an analysis of the stones, though in a 

 thorough examination of the soil their character and probable composi- 

 tion should be recorded. 



Further mechanical analysis of the portion passing the 3 millimetre 



