So, I have a problem using the Volumetric shaders in cycles. When I am viewing them in the viewport, they seem to be coming out perfectly fine, whereas when I render them, only the glass surface is visible and no light scattering/absorption occurs.
The Preview in the Viewport
The Rendered Image
(Sorry I have used a very low resolution, but the difference hopefully is clear)
[Edit] You can find my blend file here.