The counter current apparatus was the heart and the most complex part of the entire early
development of Penicillin in Oxford. With the raising of the scale of the production of Penicillin and the brewing of more and more culture
medium the researcher in Oxford needed to develop bigger and more efficient extractors to increase the amount of the Penicillin production
significantly. The new counter current apparatus had a weekly output of about 500 litre of crude broth and a capacity of about 12 litres per hour.
Norman Heatley built most of the used equipment for the Penicillin extraction by himself and even ordered parts such as vitreous
collecting bottles from elsewhere around Oxford. The influence and the contamination by air was a complete disaster
and destroyed a lot of the active substance because some air organisms have produced an enzyme which destroys the Penicillin substrate.
The basic construction of the counter current apparatus is mainly divided into 4 sections. The first section is the crude broth section which is the part for the culture medium. This is where the 1 gallon collecting bottle from step 2 is to be found. A Buckner funnel was used to have a control of the fluid of the crude broth. The second section is the 10% phosphoric acid section with a 1 gallon bottle as well. Here, a special funnel was prepared without parts of rubber to control the flow of the phosphoric acid and the amyl acetate. The phosphoric acid will be mixed with the cooled crude broth to an acidified solution with a pH value of about 2. The third section would be the amyl acetate section with a smaller bottle, with a volume of about a halfgallon. The amyl acetate is important to extract the precious Penicillin substrate from the acidified solution. This extraction will happen inside of the extraction unit, the fourth and the most important section of the counter current apparatus.