GNOME Split is a tool that allows you to split files and merge them back. It is written in Java and uses a GTK+ user interface (thanks to the java-gnome project). The goal is to offer a native implementation of similar projects which can handle multiple file formats (e.g. Xtremsplit).
Install GNOME Split on ubuntu
Open the terminal and run the following commands
sudo add-apt-repository ppa:gnome-split-team/ppa
sudo apt-get update
sudo apt-get install gnome-split