libxml: uninitialized constant

Hi all!

I try to use libxml-ruby with my ROR-application and get the following
error message: "uninitialized constant AdminController::XML".

From controller file:

require 'rubygems'
require 'xml/libxml'
...
parser = XML::Parser.new

And the same code in irb work correctly:

irb(main):001:0> require 'rubygems'
=> true
irb(main):002:0> require 'xml/libxml'
=> true
irb(main):003:0> parser = XML::Parser.new
=> #<XML::Parser:0x7fc460cf11c0>

Why it doesn't work in Rails?

(Rails 3.0.0.beta4, libxml-ruby-1.1.4)

Fix problem. It was necessary to add in Gemfile string "gem 'libxml-
ruby'".