PllVSICAI, C'(.>Ml'lKSri'K>\ OK C'aI'K C(>I.(•N^ Sftll.S. 1)1 



of soil pai'ticU's are freiiucntlv tlic riclicst fi'oiu a chcinical point of 

 view. 



Kefereucf has heeu made to Snvdei's apportionment of ditierently 

 graded soils to specific crops, but why such classes of soil should l)e so 

 specially suited to sonie crops, and not to others, has not been fully 

 stated. A partial solution may be found in the fact that it is a char- 

 acteristic feature of each kind of plant that it requires for its develop- 

 ment a certain degree of soil heat, and specific amounts of moisture ; both 

 of these are dependent upon the mechanical condition of the soil. Now, 

 according to Snyder, soils of the class that he pieseribes as best suited 

 for potatoes are so suited because such soils generally c(mtain from ~) to 

 12 per cent, of water; similarly, those which he recommends for fruit 

 usually retain from 10 to 1.*^ per cent, of water; those which are recom- 

 mended for corn slutuld, according to the same authority, contain about 

 1") per cent, of water; grain soils, he says, ought to hold from 18 to 20 

 per cent, of moisture. These, naturally, are intended to apply to 

 certain parts of the United States of America. In the Cape Colony 

 we know jis yet neither whetlier soils physically composed as above 

 would retain the proportions of moisture stated, nor whether such 

 proportions woukl be the optima for the classes of crops mentioned. 

 What needs to be ascertained here is, first of all, what the mechanical 

 condition of the soil is in localities where these crops do well, and 

 next, how much moisture these soils are capable of retaining. It was 

 to give a start to research along these lines that the investigations 

 recorded c>n the sulisequent pages were initiated. 



JMktiiod of Mkciianical Analysis of Soil. 



The complpic sifting process used in the Government analytical 

 laboratory includes the employment of the following sieves : — 



(1) A brass-bottomed sieve with circular perforations 3 mm. in 



diameter. 



(2) A similar sieve with perforations 2 mm. in diameter. 



(3) Another .similar sieve having perforations 1 mm. in diameter. 



(4) A Kahl's (Hamburg) " Messingdrahtsieb No. 50" — 



lateral measurement of meshes, -So-'SO mm. 

 diagonal ,, ,, „ --IS-'oO ,, 



(■"») A Kahl's (Hamburg) "Messingdrahtsieb No. 100" — 

 lateral measuiement of me.shes, -l-t-'lT mm. 

 diagonal „ ,, ,, •22-24 „ 



(0) An Ehrhardt k Metzger's (Darmstadt) " Florsieb No. 16"— 

 lateral measurement of meshes, -09 mm. 

 diai^onal ,, ,, ,, "11 ,, 



^^»r the mechanical analysis of soils all the above sieves are u.sed, 

 and the sifting process is further supplemented by sedimentation in 

 water. When a chemical analysis is the chief object, sieves Nos. 1, o 

 and 4 only are emj)loved. 



