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DNA: the King's story

Early equipment and images

X-ray apparatus at King'sX-ray apparatus at King's At first, the Wilkins team used a camera attached to a war surplus x-ray tube borrowed from the Admiralty. When the x-ray tube burned out, they began to use a 'Unicam' camera fitted to a Raymax x-ray tube belonging to the Chemistry Department at King's.

This was situated in the basement of the College overlooking the river Thames. Using this arrangement, Raymond Gosling produced among the first clear diffraction images of DNA.

Anyone not involved in this depth of science would be surprised that the scientists could deduce anything from the first images secured.

Like other crystalline diffraction pictures, these resembled a pattern of dots in different positions and of varying degrees of resolution and clarity.

Unicam cameraUnicam camera Despite being blurred, they convinced Wilkins and Gosling that with better equipment, they could do more. Key to this work was controlling the humidity of the samples and preventing distortion of the image over time.

Exposure times were typically 4-5 hours; some were considerably longer - the total time taken to obtain a single diffraction picture could be up to 100 hours.

It was found that passing hydrogen into the camera helped to reduce scattering caused by molecules of air, which otherwise caused fog on the film.

Regrettably, hydrogen used to leak from the joint with the collimator. Wilkins suggested a condom would seal the gap. It did!

PaperclipPaperclipIn early experiments fibres to be photographed were mounted on a frame – a bent paper clip.

With the help of the paper clip and the condom, Gosling took the photographs that convinced Wilkins and others that they were on the right track.

As well as the condom and paperclip, the team often used other makeshift apparatus to mount the samples and carry out photography. Raymond Gosling recalls visiting Woolworth's and other stores in the Strand to obtain quick drying cement and similar props.

Drum cameraDrum cameraWilkins and his team also utilised a number of other bespoke cameras to produce clearer images of DNA under carefully controlled conditions, including a drum camera designed by Len Pitches.

The risk of hydrogen escape and explosion was ever-present, one reason why many experiments were carried out at night to minimise the danger to other staff and students who congregated in the lecture theatre above the laboratory situated in the first basement of King's.

Radiation also posed a potential risk and staff wore radiation badges on their lapels to measure exposure.

By the time Franklin had been recruited new and better equipment had been secured to produce higher resolution pictures.

Two cameras in particular proved critical. The Philips micro-camera was mounted on a bespoke stand to allow the orientation of specimens.

Crucially, it utilised a prototype Ehrenburg-Spears microfocus tube generously provided by Birkbeck College and adapted in the King's Physics laboratories. This enabled a finer, more intense beam of x-rays to be produced.

A special tilting micro-camera was also fabricated by Len Pitches in the King's workshops and mounted on one of his precision stands. Together, the cameras enabled Franklin and Gosling to produce the best ever results under conditions of controlled humidity.

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