Magnesium Nitrate for RH Control

In Instance 16:47, Lorraine Schnabel asks for information about the
use of magnesium nitrate for RH control.

A saturated solution of magnesium nitrate has been used in museums
for many years to maintain a constant RH of about 53%.  Although
rather out of favour these days, saturated salts offer a reliable,
low-tech, low maintenance method of humidity control.

Magnesium nitrate is stable in solution and is reasonably non-toxic.
It is an oxidising agent so spillages would assist the combustion of
organic materials.

One problem with salt solutions is that they tend to creep out of
their containers.  However, magnesium nitrate does not suffer
greatly from this--see

    Astrup, E. E. and Stub, K. E. H.
    "Saturated salt solutions for humidity control of showcases:
    conditions for a successful system"
    ICOM-CC 9th Triennial meeting, Dresden 1990, 577 - 582.

Dr Barry Knight
Senior Conservation Scientist
English Heritage
London
+44 20 7973 3000
Fax: +44 20 7973 3001


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                  Conservation DistList Instance 16:49
                Distributed: Thursday, February 20, 2003
                       Message Id: cdl-16-49-004
                                  ***