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IX. Chemical Notices from Foreign Journals. 

 By E. Atkinson, Ph.D., F.C.S. 



[Continued from vol. xxxii. p. 390.] 



PFAUNDLER has published a number of determinations of 

 the thermal capacity of various kinds of soils*; the ideas 

 which have guided him in this investigation may be stated as 

 follows : — 



Liebig showed that the substances entering into the structure 

 of the plant fall into two groups, one of which preferably comes 

 from the atmosphere and is always presented in the same and 

 sufficient quantity, while the second comes from the soil and 

 varies in composition. Hence it was natural to ascribe the dif- 

 ferences in the growth of plants to this different chemical com- 

 position. Under similar climatic conditions, soils which furnish 

 the same nourishment must be able to produce the same vege- 

 tation. A difference in vegetation must be considered due to 

 a difference in the composition of the soil. 



These views received support partly from direct experiment, 

 partly from observations on the natural occurrence, for instance, 

 of special plants on a soil containing lime, or on one free from it. 



Liebig's view is now no longer tenable, at any rate in the ex- 

 tension originally given to it. It has been shown that the com- 

 position of the soil, though of great, is not of exclusive influence. 

 Many plants have not the power of selection : they take, for in- 

 stance, instead of a certain quantity of magnesia, a correspond- 

 ing quantity of lime without any change ; while, on the other 

 hand, a slight alteration in the physical condition of their sub- 

 soil far more affects their growth. These facts may be foreseen 

 if we consider that the circulation of matter is causally connected 

 with a circulation of forces to which these substances owe their 

 motion. 



Not merely must there be mineral constituents ; force is also 

 needed to raise them. And as the mineral constituents are not 

 very soluble, they must be presented to the plant in very dilute 

 solutions, for which purpose large quantities of water have to be 

 raised. This requires a considerable expenditure of force, which 

 is obtained by the consumption of a corresponding amount of 

 heat. Most of the water evaporates on the surface of the leaves. 

 Hence this water not merely takes from the plant the quantity 

 of work accumulated in it, but also a fresh quantity, the latent 

 heat of evaporation. The explanation of the raising of the 

 sap by capillary or endosmotic forces is not in disaccordance 



* Poggendorff's Annalen, September 1866. 



