CTATE PJLANT BOARO 
 
 January 1954 ^ ET-313 
 
 United States Department of Agriculture 
 
 Agricultural Research Service 
 
 Bureau of Entomology and Plant Quarantine 
 
 A TRANSPARENT DRYING AND ABSORBING UNIT FOR USE 
 WITH THE THERMAL-CONDUCTIVITY GAS ANALYZER 
 
 By G. L. Phillips 
 Division of Stored Product Insect Investigations 
 
 The thermal-conductivity gas analyzer, described in E-851p is 
 very versatile. Its cell unit is arranged to measure a gas against a 
 sealed air reference, or a wet or dry gas against a wet or dry air 
 reference. When this analyzer was used for checking gas concentra- 
 tions in routine fumigations, a sealed air reference was used, which 
 required a drying agent. Models available at that time were equipped 
 with a metal drier unit, and it was necessary to open the unit and re- 
 move the drying agent to determine its condition, A simple and efficient 
 drier has now been constructed in which the drying agent is visible and 
 the amount of its exhaustion easily discernible at a glance. 
 
 The drier may be made, as shown in figure 1, from a 5 -inch length 
 of 1 1/2 -inch Lucite tubing with a 1/8 -inch wall thickness. This material 
 makes a light and almost unbreakable drier. The tubing is enclosed 
 within a holder of metal strapping 1/2 inch wide, such as is used around 
 crates. A small suitcase fastener is soldered to one side of the holder 
 so that, when the tubing is inserted and the fastener snapped down, the 
 tubing is made airtight. Flanged stoppers are used as gaskets between 
 the tubing and the holder. A 1/8 -inch needle valve and a 1/8 -inch elbow 
 with a short length of l/4-inch copper tubing are used to connect the 
 drier with the gas analyzer and the pump. 
 
 The drier is installed on the outside of the gas analyzer. It may be 
 held in place by a coiled spring, one end of which is fastened to the 
 analyzer and the other equipped with a hook that is easily slipped over a 
 screw head, or both ends may be fastened and the spring pulled out to 
 allow the drier to be inserted. 
 
 For gas analyzers equipped with a pump that has a valve to control 
 the rate of flow, a simpler drier may be made by inserting a rubber 
 stopper at each end of a piece of Lucite tubing. A hole is nnade in each 
 
 ij Analysis of Methyl Bromide by Measurement of Thermal Con- 
 ductivity. 
 
liiiiiiBi 
 
 stopper and a short length of l/4-inch(o.d.) Saran or copper tubing in- 
 serted for placing the drier in the line between the analyzer and the 
 sample. 
 
 The drier may be filled with an absorbing agent, such as Caroxite, 
 to remove any carbon dioxide that occurs during the fumigation of certain 
 plants packed in moist peat. It may also be used to remove one component 
 of a mixture of gases, aftei- passage through the first part of a double-pass 
 unit. 
 
 Figure 1 .--Transparent drying and absorbing unit: 
 
 A, Metal holder for Lucite tubing 
 
 B, Lucite tubing and flanged stoppers 
 C^, Assembled unit 
 
 Photo by G. J. Baetzhold.