122 abstracts: physics and chemistry 



physics. Conceptions useful to the plant physiologist or ecologist are 

 especially emphasized. The titles and main conclusions of the individ- 

 ual papers are as follows : ( 1 ) The physical condition of soils. — The range 

 of physical conditions possible to a soil is determined by its ultimate 

 physical nature or character, that is by the nature, size, and number 

 of the particles of which it is composed. The physical condition, within 

 this fixed range, is controlled by the moisture content by virtue of the 

 surface tension on the water films between the soil grains. (2) Move- 

 ments of soil water. — The capillary actions in the soil are controlled by the 

 forces of surface tension on the water films. Permeability is a matter 

 of the size of the individual interspaces of the soil, not of their total 

 amount. (3) Soil ivater and the plant. — A very important but much 

 neglected factor in the movement of water from soil to plant and through 

 the plant is the evaporating power of the air. (4) Physical consta?its 

 of the soil. — A critical examination of the various measurements which 

 have been proposed as characteristic soil constants shows that all are 

 in some degree unsatisfactory. The mechanical analysis in particular, 

 is much less adequate than is usually believed. It is probable that 

 another and better constant can be developed out of the water equiva- 

 lent and the critical moisture content. (5) Soil temperatures. — -The 

 main effect of the soil character upon its temperature is due to its water 

 capacity. The wetter soil warms and cools more slowly. E. E. F. 



ANALYTIC CHEMISTRY. — The determination of sugars in grain 

 and cattlefoods. A. Hugh Bryan, A. Given and M. N. Straughn. 

 Circular 71, Bureau of Chemistry. 



The determination of sugars in vegetable materials, either fresh or 

 dried, having large quantities of starch, gums, fiber, etc., presents many 

 difficulties. Methods for such determinations are few and in most 

 cases are not explicit. 



Extraction with hot water dissolves the sugars but also gelatinizes 

 the starch and therefore produces changes in the sugar content, while 

 cold water extraction causes the enzymes if present to become active 

 and hence to change the sugar content during extraction. To inhibit 

 the enzyme action alkalies are often added and the extraction carried 

 on in the cold. A comparison of a method based on this procedure 

 and of a method of extraction using 50 per cent alcohol has been made 

 and as a result it is shown that with some substances the two methods 

 give concordant results but the alkaline water extraction method is 



