﻿KTLN DRYING HANDBOOK. 57 



of the condensed water to the traps. Suitable gratings or runways 

 should be provided, so that the men entering the kiln can do so \. itli 

 safety and without walking on the pipes. The interior iron work 

 and pipes should be protected by a good kiln paint, or the pipes can 

 be painted while hot with a mixture of cylinder oil and graphite, if 

 preferred. The coils should be inspected occasionally to make sure 

 that they are all working, and the traps should be observed every 

 day. 



CALIBRATION AND ADJUSTMENT OF INSTRUMENTS. 



Success in all except the easiest kind of kiln drying depends upon 

 the accuracy of the instruments and apparatus used in the regula- 

 tion of the kiln and in the determination of the moisture content. 

 It is therefore essential that the apparatus be maintained in an ac- 

 curate operating condition. Most important is the matter of tem- 

 perature indicating, recording, and regulating instruments, since 

 through them both temperature and humidity are determined and 

 controlled. 



THERMOMETERS. 



The simplest and most satisfactory way to calibrate indicating and 

 recording thermometers is to compare them at different tempera- 

 tures within their range with a standardized or calibrated ther- 

 mometer of known accuracy. Each operator should have at least 

 one such standard thermometer. The type recommended is a 12-inch 

 glass chemical thermometer, with graduations in degrees Fahren- 

 heit etched on the stem, and having a range of 30° to 220° correct 

 for ordinary purposes. Such a thermometer can be purchased for 

 about $3 list price ; and a brass protecting sleeve or case, recom- 

 mended for use in kilns, can be had for about $1.50. 



The usual laboratory method of calibration by comparison with a 

 standard thermometer consists in immersing the standard and the 

 thermometers to be calibrated in a vessel of water, which is con- 

 stantly stirred to keep the temperature uniform throughout. The 

 water is gradually heated, and the thermometers are read at intervals 

 of a few degrees. The difference between the reading of any ther- 

 mometer and the standard at any temperature is the error of that 

 thermometer, and a correction of this amount must be applied 

 to the reading to give the correct temperature. If the standard reads 

 higher, call the correction plus (-)-) and add it to the reading of the 

 thermometer, and vice versa. This method isjapplicable to glass- 

 stem thermometers and other portable types. Wet-bulb thermome- 

 ters are calibrated this way also, the wicks being removed during 

 calibration. Once every six months should be sufficient for the cali- 

 bration of glass thermometers. 



Recording thermometers require more attention than other types 

 on account of the comparative ease with which they may become de- 

 ranged. They should be calibrated in water, as described for glass 

 thermometers, the bulb and about a foot of the tube being im- 

 mersed. This calibration will give a good idea of how the error, if 

 any, varies throughout the operative range of the instrument. After 

 calibration the instrument should be mounted in place in the kiln 

 and then checked up at several points in its range by comparison 

 with the standard thermometer hung close beside its bulb. These 



