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Apparatus For Control of Moisture, Temperature, and Air Composition in Microbiological Respiration Experiments
Author(s) -
Bartholomew W. V.,
Broadbent F. E.
Publication year - 1950
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1950.036159950014000c0034x
Subject(s) - agricultural experiment station , citation , environmental science , library science , operations research , agriculture , computer science , engineering , geography , archaeology
CONTROL of moisture content and of aeration is frequently desirable in conducting many kinds of microbiological respiration experiments. Such control apparatus is of maximum utility if it can be constructed easily and from inexpensive materials and be kept in operation with a minimum of service upkeep. The apparatus and techniques described herein were developed and tested for use in plant decomposition experiments and represent a number of years experience in the study of control in respiration experiments (1, 2). The essential parts of the apparatus are: capillary tubes for control of air flow rates; volume overflow tubes for control of pressure gradients and for dissipation of excess quantities of air; chambers for control of moisture in the air stream; mixing chambers for regulation of air composition; containers for the experimental samples; and absorption tubes for recovery of carbon dioxide and ammonia. The capillary tubes for air flow control are simple to make and have been found satisfactory in operation. The principle upon which they operate is merely a restriction in gas flow by a small orifice as illustrated in A, FigI. ' Construction and calibration of the capillaries is simple and direct. Small uniform lengths of small bore capillary glass tubing are heated and one end drawn out to a very small diameter, 0.2 to 0.5 mm. The resulting capillary is placed in series with a flow meter, a constant and known air pressure gradient is applied, and successive segments of the small end of the capillary are broken off until the proper flow rate is attained. After one capillary has been calibrated under standard or controlled conditions, other capillaries may be calibrated by comparing with the standard on an ordinary bubble counter. This latter apparatus may be constructed by connecting a pettenkoffer tube in series to a constant source of gas pressure and to the capillary. The flow rates of the several capillaries can be compared in terms of bubbles per minute through the pettenkoffer tube. As long as the bubble rate is not excessively rapid the flow rate will be approximately a linear function of the number of bubbles per time unit. The equation for the steady state flow of gases in linear systems given by Muskat (3) is _ kyo (P2 + •" — P^ + ) Q== / t ( l +m) L where Q = rate of mass flow per unit cross section, yo = density at standard conditions, /j. = the viscosity of the gas, k = the permeability of the medium, specific heat at constant volume m = —i—r;=—;,' and where P.,, specific heat at constant pressure Pj are the boundary values of the pressure at X = O, L. For isothermal flow, m = 1 and the equation becomes