Re: What is the lowest level of humidity a deliquescent substance can work at?

Deliquescent substances each have their own level of humidity at which 
deliquescence occurs. Below this level of humidity no solution is formed. 
This is called the deliquescence relative humidity (DRH). Interestingly, 
a recent research by Yang, Pabalan, and Browning (see the Materials 
Research Organization website - http://www.mrs.org/) suggests that 
solution formation begins well below the DRH as evidenced by increased 
ion mobility in the solid even though no visible sign of solution 
formation is observed. They also experimented with many combinations of 
deliquescent salts and found that the DRH of the mixtures were always 
lower than the DRH or any of the component salts. I don't know the answer 
to your second question but based on these findings I would guess that it 
would be a mixture of deliquescent salts. A quick search on the internet 
should turn up the most common deliquescent materials.