Image disappearing with depth

I went to this link http://www.codeguru.com/opengl/oglwrapperclass.shtml
and downloaded the demo project. I then went to the function OnDrawGL() which is a member of the class CTestGLView. Right after the command glPushMatrix(); I added the command glTranslatef(0, 0, -6); to make my image appear farther into the screen. I noticed now that when I run the program, and rotate the image by dragging with the mouse, some of the image disappears when it goes beyond a certain depth. Why does that happen, and how can I stop it?

Maybe your Far clipping plane is not so “far”.
You can set the view distance with:

void gluPerspective(
GLdouble fovy,
GLdouble aspect,
GLdouble zNear,
GLdouble zFar
);

where zFar and zNear set the distance from the viewer of the clipplanes.

Get more info on msdn or another guide.