setting a cookie to be used across web apps

I have a number of apps all under the same domain: E.g.:

app1.overflow.com app2.overflow.com/email app3.overflow.com/home

I setting using these functions: http://www.elated.com/articles/javascript-and-cookies

How can I setup the cookie so that It can be read across all of the appli开发者_运维问答cations?

I dont seem to be able to get this to work?

Try specifying cookiename=cookievalue; domain=overflow.com; path=/ when setting the cookie.