This Cohn Bros 27oz Soda Syphon featured a ribbed shape.

Further Information

In this image the Soda Syphon is pictured with a 6 o'clock Lager bottle.

If you look closely at the 6 o'clock Lager bottle you can see the watermark above the label showing "CB" inside a ring, with "Bendigo" imprinted above and "Swan Hill" imprinted below. The Swan Hill factory was established by Leo Cohn in 1923, so this bottle must have been produced after 1923.