[Mark C]

UPDATE:

Here's the temperature vs. RH data for NaCl (table salt). I copied this from a post at the Stogie Guys blog. While I can't site a specific source, I found one or two other pages online that agree with these numbers. This should give you a better idea exactly how negligible the ambient temperature is for this test.

Degrees Celsius versus RH of saturated salt solution:
0*C
75.51 ± 0.34 % RH
5*C
75.65 ± 0.27 % RH
10*C
75.67 ± 0.22 % RH
15*C
75.61 ± 0.18 % RH
20*C
75.47 ± 0.14 % RH
25*C
75.29 ± 0.12 % RH
30*C
75.09 ± 0.11 % RH
35*C
74.87 ± 0.12 % RH
40*C
74.68 ± 0.13 % RH
45*C
74.52 ± 0.16 % RH
50*C
74.43 ± 0.19 % RH
55*C
74.41 ± 0.24 % RH
60*C
74.50 ± 0.30 % RH
65*C
74.71 ± 0.37 % RH
70*C
75.06 ± 0.45 % RH
75*C
75.58 ± 0.55 % RH
80*C
76.29 ± 0.65 % RH

I'd appreciate it if a mod could append this to my original post. Thanks!