Comment 2 for bug 95565

$ sudo apt-get install emerald
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package emerald is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package emerald has no installation candidate

Also, if you search here: http://packages.ubuntu.com/cgi-bin/search_packages.pl?keywords=emerald&searchon=names&subword=1&version=all&release=all

You can see the only packages available are emerald-themes and xemeraldia, so no emerald.