Franlkin’s oil experiment

Calming the waves at Brutti & Boni

Brutti And BoniBrutti & Boni is a fairly new Italian cafe in South Kensington. Located at the less busy end of Gloucester Road, it was quiet when we popped in to try it a couple of weeks ago. The bright interior has light coming from a roof window at the back of the shop, though it seems that many people opt to sit outside with their espresso in the morning, watching the traffic go past. They serve Caffe Molinari coffee together with a good selection of Italian food items. All in all, a good place to go if you are in the area visiting the Science, Natural History or Victoria and Albert museums and fancy a break and a relaxed coffee nearby.

Inside, the shelves are stacked with various Italian condiments, pasta and olive oil. It was this that prompted me to visit Clapham Common to retrace the steps of Benjamin Franklin. Franklin of course was one of the founding fathers of the USA. He was also a keen scientist, diplomat, printer, in fact the man in some ways defines the word “polymath”. His interests and importance span so many areas that it is difficult to write a two-sentence description of him. Fortunately, for the purposes of today’s Daily Grind, I do not need to. Today, all that is important is that Franklin did some experiments on Clapham Common with oil.

Shelves of olive oil at Brutti & Boni

Shelves of olive oil at Brutti & Boni

Franklin had been investigating the “old wives tales” that a small amount of oil placed onto water ‘calmed the waves’. In fact, the old wives tales can be traced back to Pliny (the Elder) in his Natural History written in around 77AD. Pliny had written of pearl divers and how they sprinkled oil on their faces so that the water above them became calm, allowing them to see the oysters that they were looking for on the sea bed. Franklin himself describes, in his letter to the Philosophical Transactions (1774), an event that he experienced in 1757 while sailing to the UK. Noticing that the wakes behind two of the boats in the fleet were calm, he describes how he asked his ship’s captain about this curiosity. Replying slightly dismissively, as if to someone who is quite ignorant of the workings of the world, the ship’s captain replied that “The cooks… have I suppose been just emptying their greasy water through the scuppers, which has greased the sides of these ships a little”. Obviously it was common knowledge that oil calmed the waves.

So, one day in the 1760s, Franklin took a walk to Clapham Common and to Mount Pond. Emptying about a tea-spoonful of oil (oleic acid) into the pond he watched as the oil produced an “instant calm [on the pond] over a space several yards square, which spread amazingly, and extended itself gradually till it reached the lee [opposite] side, making all that quarter of the pond, perhaps half an acre as smooth as a looking glass.” Oleic acid is the principal component of olive oil. Franklin had effectively calmed the waves on the pond with a mere tea-spoonful of olive oil.

A view over Mount Pond, Clapham Common

A single tea spoon of oil would calm the ripples on Mount Pond, Clapham Common

We can calculate how thin the layer of oil had become by dividing the volume of oil in a teaspoon (5cm³) by the area of half an acre (2023 m²) to get an oil layer that was 2.5 nm thick. To put this in perspective, a coffee bean of width 7 mm would fit nearly 3 million of such oil layers in itself width-wise. Later, more precise, measurements of the thickness of such an oil layer, by Lord Rayleigh and Agnes Pockels, gave 1.6 nm and 1.3 nm respectively. This is approximately the length of a single oil molecule. It seems that the waves on water can be stilled by a single molecular layer of oil. How does this work? Why not let me know what you think in the comment section below.