[15] Page 79. _Solution of a Salt._--Acetate of soda. A solution
saturated, or nearly so, at the boiling point, is necessary, and it
must be allowed to cool, and remain at rest until the experiment is
made.
[16] Page 86. _Binoxide of Nitrogen and Hypo-nitrous Acid._--Binoxide
of nitrogen is formed when nitric acid and a little water are added to
some copper turnings. It produces deep red fumes as soon as it comes
in contact with the air, by combining with the oxygen of the latter to
form hypo-nitrous acid. _Binoxide of nitrogen_ is composed of two parts
oxygen and one part of nitrogen; _hypo-nitrous acid_ is composed of one
part of nitrogen and three parts of oxygen.