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Oertling balance from a golden era

Oertling balance from a golden era

Date Published: 29-Oct-15

If you’ve visited ChemCentre in Bentley, you’ll know that our staff work in state-of-the-art facilities that house equipment fitting of a twenty first century laboratory. But it wasn’t always so, and with the move from our East Perth laboratories in 2009, ChemCentre staff had to make difficult decisions about a range of equipment that had served the public well for decades. The East Perth facility held a treasure trove of antique instruments and, fortunately, many were rescued before the building was demolished in May this year.

The collection gives a fascinating insight into ChemCentre’s history and the development of analytical techniques and instrumentation over time. Among the collection is an Oertling balance used from the 1950s to the 1980s to measure the weight of precious metals.

The Oertling balance, named after the German instrument maker Ledwig Oertling, measured the weight of objects up to 20g with startling precision. The sensitivity of the balance allowed scientists to obtain a reading to six decimal places or one microgram (0.000001g), lighter than the mass of a human eyelash.

Barry Price, team leader of mining chemistry has been working at ChemCentre for more than forty years and used similar balances early in his career. “A precision of one microgram is incredible for the period the balance was in use; even our top electronic balances today can only just reach such precision,” Barry explained.

Close up of balance fulcrum
The sensitivity of the balance comes from the precise weights on the right side of the balance beam.

Balances such as this were used by ChemCentre to weigh the mass of gold beads, the product of fire assay used to determine the gold content of a sample of ore. The complicated process included mixing a combination of salts with approximately 30g of crushed ore and heating it to 1000C. As the rock melted, lead would combine with the gold to form a solid ’button‘. The lead was then removed from the button leaving behind a gold bead. The Oertling balance was used to weigh the gold bead and determine exactly how much gold was in the original 30g of ore.

The gold content was used to advise mining companies as to whether an ore was financially viable to mine, which made the accuracy of the Oertling balance crucial.  When the gold in 30g of ore is used to predict the quantity of gold in thousands of tonnes of ore, a difference of several micrograms could result in a difference of hundreds of kilograms of gold for the mining company.

While this process and balance is no longer used at ChemCentre, Barry says it’s a great reflection of ChemCentre’s strengths and history in chemical analysis for the mining industry. “We’re always looking to improve our techniques and instrumentation. Our clients demand the highest quality and without continual development we wouldn’t be able to meet and exceed expectations,” he said.

The Oertling balance will be on display in the reception of our Bentley laboratories in the near future.

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