File:Moisture content and physical condition of soils (1908) (14803760323).jpg

Identifier: moisturecontentp50came (find matches)
Title: Moisture content and physical condition of soils
Year: 1908 (1900s)
Authors: Cameron, Frank K. (Frank Kenneth), 1869-1958 Gallagher, Francis E., jt. author
Subjects: Soil moisture
Publisher: Washington, Govt. print. off.
Contributing Library: U.S. Department of Agriculture, National Agricultural Library
Digitizing Sponsor: U.S. Department of Agriculture, National Agricultural Library

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forit is brought downfirmly against theend block B. Sincethe wooden verticalsupports are cut Vshaped, the half-round section ofbrass tubing fitssnugly into place.This method hasproved well suitedto soils having thepower to retain theform of the cylin-drical soil columnirrespective of themoisture content.Some soils, how-ever, can not besucce ssfully han-dled in this way. either because when wet they become incoherentand do not retain their form or because when dry they crumble.The method is not well suited for continued observations on wettingand drying of the same soil sample, because, as has been pointed outin a previous chapter, the volume changes tend to cause cracking ofthe soil: the>e cracks become points of weakness and in time cause thebreaking down of the soil column.Micrometer method. In order to get around the difficulties just described the mi-crometer method was devised, in which the soil sample is bettersupported, being held in a cup. The form of apparatus is shown in
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Fig. 33.- -Apparatus for micrometer method of measuringchanges in soil volumes. APPARATUS AND METHODS. 69 figure 33. The soil sample is contained in a cup C. which has a per-forated bottom through which the soil may be wetted. This cuprests directly on the metal table of an adjustable stand, to which themicrometer screw is also attached. This method of support has adistinct advantage, since there is little possibility of the table andmicrometer changing their relative positions and thus affecting theresults. The variation in the height of the soil surface is measuredby means of the micrometer screw M. A brass plate P with a pro-jecting short vertical shaft rests on the surface of the soil. Themicrometer point is brought just into contact with the top of theshaft. The contact is determined in the same manner as describedin the preceding method. In order to obtain a good electrical con-tact with the plate P without disturbing its position in any way. adrop of mercury is held in a depres

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