wIth saturated salt solutIOns of sodium dichromate and magnesium nitrate. ' 1. ... salt solution is made up as a slushy mixture with .... Lithium chloride LiCnl,O.
Journa tof Research of the National Bureau of Standards
Vol. 53, No.1, July 1954
Research Pa per 2512
Relative Humidity-Temperature Relationships of Some Saturated Salt Solutions in the Temperature Range 0 to 50 C 1 0
0
Arnold Wexler and Saburo Hasegawa . .' T he r.e lat ive hll m idity-te mp c:at llre rela t ionships h.a ve b~e n determ ined in air in equih b llum wit h sat urated ~ al t solu t IOns of llt hlUm chlonde, L1C[·H 20 ; magnesi um chloride M gCL·6HzO ; . ~odlU~n dl c!lromat~, Na2Cr207 ·2H~ O ; magnes ium n itrate, Mg (N 0 3!2·6H 2 0 ~ sodlU~ chlonde, Na CI; amm OJ1Jum sulfat e, (N H 4),S04; po tassium nitrate, K N O; ; and potas8 1um r~u lfate , ~( 2S 04' ~v~r a. te mpera:t ure ran ge of 0° to 50° C, using t he d cwp oint method . 1h.e rel.atlve hlllJ1J.d lty r ~s a con t muous func tIOn of te mperat ure, and , excep t for sodIUm chlor!de, IS mO~l otO I1JC. 1he curve fo r sodium chloride in creases from 74. 9-p crccn t Tela tJ v,e hlllnlClt ty at 0 C~? a maximum of 75. 6 l)er ce n t a t 30° C a nd t hen g radu all y d ecr ease8 to 7~. 7 per cent. 1he. ~ax lmum change 111 reJ ~tlve humidi ty with temper at ure, al?ou t 1.5-petcent re lat ive. h lllTIldlty as t he te m pe rature 111 creases f rom 0 ° to 50° C occu rs wIth sat urated sal t solu tIO ns of sod ium dichro mate a nd m ag nes ium ni trate. '
1.
The dewpoin t m ethod was u tilized in this investiga tion. Wi th this m ethod, m easurem en ts could readily b e mad e in the presen ce of an air atmosphere under condi tions similar to those occurring in the use of sa tura ted sal t solutions for humidity-control purposes. Furthermore, o th er th an using cb emically pure sal ts of r eagen t gr ade and distilled wa ter no sp ecial precau tions wer e taken. Thus th e ~alts con tained trace impurities, and the water was ail' sa tura ted .
Introduction
, Saturated sal t solu tions are very useful in producmg lmo~n re~ative humidities, principally for testing and cahbratmg selec ted hygrometers and hygrographs at temperatures above 0° C. The sa tura ted salt solu tion is made up as a slu shy mixt ure with distilled water and ch emically pure sal t in a Q'lass or enameled t ray and is enclosed in a sealed ~e tal or glass chamb er. WJ1en equilibrium conditions, usually ,h asten ed by forced air circulation or stirring, are a ttam ed, the ch a mber space is at a constan t r elative hum~dity. ~o::n.e saturated salt solu tions produce relatIve humIdItIes t hat ar e roughly indep endent ·of temperat ure. The equilibri~m valu es of r elative humidi ty of th e saturated solutIOllS of several sal ts used in calibration a nd testing are listed in NBS Circular 512 [1] 2 ~nd ar c based .p ar tly
