Category: Coffee review

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cafe with good nut knowledge Coffee review Science history slow

Spinning a yarn at E&J’s Pantry, Endell St.

E&J's Pantry on Endell St
E&J’s Pantry on Endell St

There are still a few areas of central London which seem a little short on good cafés. One such area lies just east of Covent Garden. So it was very fortunate that, on arranging to meet a friend nearby, I came across E&J’s Pantry on Endell St. The coffee is from Nude roastery and the interior, while not exactly spacious is large enough that we were able to sit undisturbed for quite some time. Along with good coffee, they serve lovely cakes which (according to their website) are made in their own kitchen. This is presumably why they could tell me confidently which cakes were nut free. (Those who follow @thinking_bean on Twitter may know that this is a bit of a hot topic for me.) I enjoyed a very good Long Black and a cake, before sitting back and taking in the surroundings.

On one of the walls inside E&J’s Pantry are a series of photographs. Each photograph is suspended by a thin thread from a rail near the ceiling. The observation reminded me of spiders webs and the (often heard) claim that spider silk is a natural material that is “stronger than steel”.

photographs, spiders web, nylon
Photographs inside E&J’s pantry. Can you see the thin threads holding up the pictures?

Unfortunately, the claim that “spider silk” is stronger than steel is a little disingenuous. For a start, there are many forms of spider silk. A ‘typical’ orb spider for example, will combine at least four types of silk to make a web. Secondly, even for the main type of structural silk (Major ampullate), the statement that it is stronger than steel is sadly pushing it a bit. The issue is that it depends on exactly how you define ‘stronger’ and the species of spider that makes the silk. Spider silk can be comparable to steel in terms of its tensile stress (how much it takes to break it), but it is when it is compared to steel based additionally on the weight of the material that spider silk can be considered ‘stronger‘. When you combine this with the fact that spider silk is more environmentally friendly (and biodegradable) than man-made comparable fibres such as Kevlar, it is clear why research is being done into understanding, and synthesising, spider silk.

A question arises. If it is so strong and so lightweight, why don’t we farm the spiders to harvest the silk? Wouldn’t this be quicker than trying to synthesise it? Clearly we weren’t the first to think this and a farmer in North Carolina, USA, tried in the 1930s. Unsurprisingly, there were issues. Firstly, it took 57000 spiders to produce 0.45 Kg (1 lb) of spider silk. Secondly, if they weren’t kept in (expensive) solitary confinement, they ate each other. It seems that the N. Carolina spider farm was not a commercial success. However, as described in the New Yorker (8th Feb, 1941), a certain Miss Mary Pfeifer did harvest spider silk in the first half of the twentieth century, for use as cross hairs in targets for surveyors and, more sinisterly, bombers. Glass engraving at the time was not fine enough for making the cross hairs. The thinnest line that could be made by a diamond cutter into glass was about double the diameter of the silk from spiders webs and so spider silk had an obvious ‘niche’ market.

HM Ng, spider on web
It takes several types of silk to spin a web. Image © HM Ng

In 1941, Pfeifer would pay “small boys” from the neighbourhood 15 cents for each useable spider that they caught and brought to her. She would then harvest the silk and wind it onto spools ready for use in target sights. Since then we have developed nanofabrication techniques which mean that very thin strands of metal (such as platinum) can be positioned onto the lenses. Continuous strips of metal of around 10 nm thickness (this is one thousandth of the width of a spider silk) can be routinely deposited. Through the development of these and similar manufacturing techniques we no longer need spider silk for use in cross hairs. It is probable that the market cornered by Mary Pfeifer no longer exists.

Spider silk however remains one of many areas where, by studying nature we get clues as to how to overcome various technological challenges. Sometimes devices possibilities are obvious, such as with the opportunity of synthesising material with the strength to mass ratio of spider silk. Sometimes however devices are a long way off. It would be a shame if we prioritised research into devices at the expense of appreciating the ingenuity of nature’s own solutions to its problems. As the story of Mary Pfeifer shows, sometimes today’s obvious devices are not those of tomorrow, who knows where research done purely out of curiosity would lead us.

 

E&J’s Pantry is at 61 Endell Street, WC2H 9AJ

More information about spiders webs can be found in “Spider Silk”, L Brunetta and CL Craig, Yale University Press, 2010

 

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Coffee review Observations Science history

A ‘brief’ encounter at Coffee Affair

Coffee Affair, Queens Road Station
The exterior of Coffee Affair, yes it really is inside the station

It was a few weeks ago now that I dropped into Coffee Affair on a Saturday afternoon and met Michael (who runs Coffee Affair along with ‘Mags’). What can I say? This place is worth visiting for so many reasons. Firstly of course there is the coffee, so much care and attention to detail was taken when I ordered a pour over Burundi coffee from Round Hill Roastery. I was warned that my coffee would take some time to prepare before the filter was carefully rinsed and the coffee weighed and ground. The final coffee having been made with such attention that I started to understand why they had chosen the name ‘coffee affair’. It is clear that coffee is a passion.

Parquet floor at Coffee Affair
The floor at Coffee Affair.

Then there is the knowledge that Michael brings to the coffee and is happy to share. Thoughts about the best temperature to drink the coffee for example, or details about different brew methods (there is a lovely array of coffee brewing equipment on the wall of the cafe). One thing that really appealed to me though was the place. There are only a couple of tables and a bar but this emphasises the space that Coffee Affair inhabits: A preserved old ticket office. There are windows looking into the station with bars on them through which the tickets used to be sold. There is the oak table that has had years of ticket sellers leaning on it, presumably with a lamp next to their counter as it would have been a lot darker when it was used as a ticket office. Then there is the flooring, original parquet flooring that dates from the time that the station was built.

If you take a seat towards the back of Coffee Affair and look at the floor you can see where the floor has worn down just that little bit as ticket sellers from years ago shuffled at their counters while selling tickets. Like the toe of St Peter, the floor has been worn away by the number of people in contact with it over the years. Between the counters you can see where someone has tried to polish the parquet to minimise this ‘dip’ but has instead managed to produce lines in a slightly more polished floor. Thinking about the wear of the floor reminded me of Charles Darwin’s musings about the erosion of the Weald in the South East of England.

Goudhurst area
How long does it take for such landscapes to form?

In the first edition of Darwin’s book “On the Origin of Species” (1859), Darwin included an estimate for the age of the Weald of Kent, the area between the chalk hills of the North and South Downs. Based on his observations of coastal erosion, Darwin calculated that the Weald must have been at least 300 million years old. This was perfectly long enough for the gradual evolutionary steps of natural selection to have occurred. As Darwin said “What an infinite number of generations, which the mind cannot grasp, must have succeeded each other in the long roll of years!”* Looking at the floor at the Coffee Affair, you can get a similar idea as to the number of generations that have stood at the ticket windows.

Darwin’s estimate of the age of the Weald led him into an argument with William Thomson (Lord Kelvin) about the age of the Earth (which you can read more about here). It was Kelvin’s argument about the age of the Earth that Darwin considered “the single most intractable point levelled against his theory during his lifetime”†. The argument was eventually settled in Darwin’s favour, once new physics had been discovered, but only after both Kelvin and Darwin had died. So I’ll leave Darwin the last words for today’s Daily Grind, relevant too for those who have the opportunity to study the floor at Coffee Affair: “He who most closely studies the action of the sea on our shores, will, I believe, be most deeply impressed with the slowness with which rocky coasts are worn away”.*

 

Coffee Affair is in the old ticket office at Queenstown Road Station, Battersea,

* Quotes from “On the origin of species”, Charles Darwin (Oxford World Classic’s edition, 2008)

†Quote taken from “Charles Darwin, The Power of Place”, Janet Browne, Princeton University Press, 2002

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Coffee review Home experiments Observations

Sugar castles at Iris and June, Victoria

Iris and June, Victoria, coffee in Victoria
The exterior of Iris and June

This post has been a long time coming. Over the past few months I’ve been popping into Iris&June to get take away coffee now and then and have got quite fond of the friendly service and good coffee. What I have not really had the opportunity to do (until recently) was sit and enjoy a coffee inside. Fortunately that’s now changed and I can add Iris&June to the Daily Grind.

So, how is I+J? Well, it is a 5 minute walk from Victoria train station and a welcome break for good coffee. They serve Ozone based espresso, with a brew bar which features guest roasts (also from Ozone) made with the V60 or Aeropress. There are a good looking selection of cakes on offer, though sadly, on the day that I could sit inside with my drink, they all had nuts in them. Hopefully another time.

Sugar jar, I&J, I+J
A jar of sugar at Iris and June

I took a seat on the cushioned bench near the wall and started to look at what was going on. It is the sort of place that is very good for people watching. My eye though was drawn to what was on my table: a jar of sugar. It is not that I take sugar in my coffee, it is that I was reminded of a tutorial I once had as a student. I cannot remember the exact conversation but it concerned piles of sand. My tutor (a theoretical physicist) had said something along the lines “Ah yes, well, of course, everyone knew the maximum angle that a pile of sand could make before it became unstable and then how it started to collapse…. Until of course someone measured it.” [laughed] “We’d got it entirely wrong.”

This ability to laugh at what we do not know, (or what we assume we do know and then measure it and find out that in fact we do not)  is one of the pleasures of physics. We are trying to understand the world we live in, we have not yet got there. Sometimes it is the smallest things that are not yet understood, such as how and why (dry) sand forms avalanches as it is piled up. Yet these small things can turn out to have big consequences (as was also the case for the understanding of coffee stains). In this case, the experiment had tested the way that a pile of sand collapsed in response to different shaped grains of ‘sand’. It had relevance then (and continues to have relevance now) not only in terms of granular dynamics: how do we predict landslides/avalanches? But also in terms of crucial theoretical models about how these processes behave. Theoretical models that are applied to systems as diverse as knowing how electrical devices (resistors) work to understanding the noise on the luminosity of stars. Realising that we were wrong enabled us to probe the question more deeply and thereby to understand it more.

There are similarities between sugar and sand, but also key differences. Although it was tempting to start building sugar castles in the sugar jars on the tables at Iris and June, I was aware of the impression that I may have made to those who go to I+J to people watch (see above). I will therefore leave it as a home experiment. How steep a sugar castle do you think you can make? And how steep can you in fact make it, what is the role of water in building sand castles?

Please leave any reports of experimental results for how steep you can make a pile of sugar in the comments section below and feel free to send me your sugar-castle pictures.

Iris and June is at No 1 Howick Place, SW1P 1WG

Categories
Coffee review General Observations

Reflections at Knockbox, Lamb’s Conduit Street

Knockbox, Knock box, coffeeKnockbox coffee is on the corner of Lamb’s Conduit Street and Dombey Street. It is a small place and we had to go twice in order to get a seat, though the compensation is that there are views all around the cafe (it being on a corner). I enjoyed a very good americano, made using Workshop coffee. Complementary jugs of mint infused water were dotted around the cafe which is always a nice touch. Sadly, I tried Knockbox just after lunch and so didn’t try any of the edibles on offer. This does mean however that I will just have to go back to try them at some point (and of course, to enjoy another coffee).

There were a lot of things to notice around Knockbox that day. There were the air bubbles in the water that had become stuck around the mint leaves. There were the light bulbs (that you can see through the windows in the picture). And there was the espresso machine: A gleaming piece of machinery that sat majestically on the counter. Looking at the espresso machine it was impossible not to be struck by the reflections from the surface. The reflections are not only testament to how much the staff at Knockbox must polish the machine; how reflections work is the subject of today’s Daily Grind.

espresso machine, metal, reflection
The gleaming espresso machine at Knock box

The interaction of materials with light is one of those fascinating areas that reveal physics at its most fundamental. I’ve often taught undergraduate physics students who are looking forward to learning about quantum mechanics because it is “weird”. This is true, quantum mechanics can be quirky, but electromagnetism (which is about light) can be just as odd. To get such elegant and surprising physics out of what is essentially all classical, nineteenth century theory, is one of those joys about learning about (and teaching, using and experiencing) this subject.

However, to return to the espresso machine and light.  How light interacts with objects reveals how the electrons are distributed in the material which in turn tells you something about the atoms that make up the espresso machine. (For how to experience electrons in your coffee, see Bending Coffee, Daily Grind, 26 Nov. 2014). As the electrons are electrically charged, they respond to light which is, ultimately, an oscillation of electric (and magnetic) field. Electrons in a metal are shared in an “electron sea” between all the atoms in the metal. Consequently, when light falls on a metal surface, the electrons can respond to the electric field oscillation of the light and they re-emit the light backwards as a reflection.

ImpFringe, #ImpFringe, Fox's Glacier Mints, linearly polarised light
Sugar rotates linearly polarised light. The ‘device’ above is made from layers of Fox’s Glacier Mints and 2 linear polarisers (eg. a pair of polarised sunglasses). Photographed at ‘Lit Up’, an Imperial Fringe event held at Imperial College London, that was free to the public.

On the other hand the electrons in the atoms of the plastic of the grinder (or the glasses on the top of the espresso machine) are held firmly to each atom. Therefore most of the light that we see will go straight through these substances with each atom acting to propagate the light forward but not able to completely block it for a reflection. Coffee beans too contain electrons that are held in place by the atoms in the molecules that make up the bean. Unlike the glass though, the electrons in coffee beans are held in atomic bonds that happen to have an “excitation energy” that is at a visible light frequency. Rather than let the light through, they absorb certain colours of light (more info in the Daily Grind here). The result is the opaque, deep brown of the coffee bean.

This year is the international year of light, a year which is intended to celebrate our understanding of light. There are so many light based processes occurring all around us at every moment. Why not stop in a cafe and see how many you can spot in your coffee cup?

Categories
Coffee review General Observations

The Corner One, Camden

20 Oval Road, Corner One
The Corner One in Camden

While browsing London’s Best Coffee, I came across a recommendation for The Corner One in Camden. The Corner One is tucked away on a side street near Camden Lock. What a great recommendation. The café itself is quite small and could be described as ‘cosy’. As the name suggests, it is on a corner, meaning that there are plenty of window seats on which to perch while enjoying your coffee. We ordered an Americano and a Flat White (Nude roastery) and couldn’t resist trying their muffins (which were very good). The atmosphere in the café was relaxed and, in a nice touch, dotted around the room were a variety of potted plants.

The strangely leaf-less plant at the Corner One
The strangely leaf-less plant at the Corner One

After a while, our attention was drawn to one plant in particular that had no leaves on it, although the flowers themselves seemed very healthy. This observation reminded us of the importance of plant life (and leaves) in the global environment and the fact that this week, diplomats from 200 countries are meeting in Geneva to edit the text agreed at the Peru climate summit. Their aim is to get the text into a form that could become a legally binding agreement at the climate talks to be held in Paris in December.

Plants are an essential part of the ecosystem of our planet. They absorb carbon dioxide and produce oxygen during photosynthesis. Another important contributor to the world’s oxygen supply are algae, as I became aware when I went to a recent Café Scientifique at the Royal Society (free and open to all). Dr Sinead Collins of Edinburgh University was describing her work on algae and what may happen to them as the oceans become more acidic. (The audio recording of the evening is available here). Ocean acidification is a consequence of increasing CO2 in the atmosphere. As CO2 dissolves in the sea water, it forms carbonic acid thereby increasing the acidity of the oceans (for more information click here). This increased acidity affects the ocean’s plant and animal life in ways that we are only just starting to understand. The evening emphasised how important it is to address the issue of climate change before it is too late.

latte art, flat white art
What the plant lacked, the coffee made up for

During the meeting, Collins mentioned that she preferred the term “global weirding” to “global warming”. The term does indeed convey the fact that a large greenhouse effect would make the weather system highly unpredictable rather than merely ‘warmer’. We should expect odd weather if we continue to pump CO2 and other greenhouse gases into the atmosphere. It is critical that the draft text currently being discussed in Geneva is agreed in Paris this year. We need a legally binding agreement to reduce our greenhouse gas emissions. Already our aim is very low; to reduce global greenhouse gas emissions to a quantity that would limit the global temperature increase to not more than 2°C higher than pre-industrial levels. Even so, this modest aim occasionally seems too high.

Let’s hope that the diplomats in Geneva this week and then the world leaders in Paris from 30 Nov – 11 Dec, agree to limit our CO2 emissions to that we can continue to enjoy our coffee.

The Corner One can be found at 20 Oval Road, NW1 7DJ.

Categories
Coffee cup science Coffee review General Observations slow

Rain drops at Notes, Covent Garden

Notes Covent Garden, rain, puddles
No one wanted to sit outside when we visited Notes at Covent Garden

It was a cold and wet afternoon in early January when I finally had the opportunity to try Notes (Covent Garden branch). Inside, there were plenty of places to sit while warming up and drying off enjoying a coffee. Although it seems small from the outside, inside, the branch feels quite open, with the bar immediately in front of you as you come through the door. One of the attractions of Notes to me, was the fact that I knew that they served different single estate brewed coffees. I think I tried a “La Benedicion” coffee, or at least that is what I seem to have scribbled in my notepad. We took a stool-seat at the window to look out at the rain as my coffee arrived in a 0.25L glass jar. It is always nice to try different single estate coffees and generally, if I know that a café serves single estate coffees I will seek them out to try them for the Daily Grind.

The reflection of the Notes sign board in a cup of tea
The reflections in a cup of tea

Watching the rain form puddles outside, my thoughts were turned to the reflections bouncing off the water in the puddle. It struck me that the appearance of puddles depends on the water molecules behaving both as individual molecules and as molecules within a group. The rain creates ripples in the puddle which can only occur because each molecule is (weakly) attracted to the other water molecules in the puddle, forming a surface tension effect. A ripple is a necessarily collective ‘action’. On the other hand, the reflection of the lights from the street is the response of each individual water molecule to the incoming light. The reflected image is made from the response of many individual molecules. Reflection is more of an individual molecule thing.

Warning sign, train, turbulence
Such turbulence should be familiar to anyone who has stirred a cup of coffee.

I continued thinking about this when I got home where it occurred to me that there was another connection between rain and coffee. It is often said that “rain helps clear the air”, or something similar. Yet this is not quite true. If you have a coffee in front of you at this instant, take a moment to drag a spoon through it. Note the vortices that form behind the spoon. Such vortices form around any object moving through a fluid. In the case of the coffee it is the spoon through the water. For the rain, as the rain drop falls through the air it creates tiny vortices of air behind it. Just as with the coffee spoon, the size of these vortices depend on the speed and size of the falling drop. These vortices pull and trap the atmospheric dust bringing it down to earth more quickly than rain alone could do. The air is cleaned more by this ‘vacuum cleaner’ action than by the ‘wet mop’ of the rain itself.

I’m sure that there are many other coffee-rain connections that you can make if you sit in a café as I did on a rainy day. Let me know your thoughts on this or indeed, on anything that you notice and think interesting while sitting in a café. There is so much to notice if we just put down the phone or close the laptop while enjoying our brew.

Edited to add: Sadly, this article was posted just as Notes Covent Garden was closing down. Notes still has branches at Trafalgar Square and in Moorgate and is opening new branches in Kings Cross and Canary Wharf in February I believe. Hopefully they will all serve single estate brewed coffee and have good window seats from which to observe the rain when it falls.

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Coffee cup science Coffee review Home experiments

Red Door, Greenwich

Red Door Greenwich, Red Door
Interior of Red Door cafe, Greenwich

Red Door in Greenwich is a great escape from the bustle of the busy streets surrounding it. Although it was crowded when we visited, it was still possible to find a table and have a conversation without too much background noise. I had heard good things about Red Door and wasn’t disappointed. Good coffee (from Monmouth), nice cake and warm surroundings. Definitely a place to go to when in Greenwich. The music that was playing was coming from a record player in the corner. A proper turn-table playing vinyl records. Suddenly, there were so many possibilities for stories for a Daily Grind article. There was the fact that records are analogue based (as opposed to the digital CDs), or perhaps I could write about the physics of a valve amplifier and how it relates to the evaporation of water from coffee (some of the physics is very similar). However what I started to get obsessed with is: what would happen if you put a coffee on a record player?

Now, I am an experimentalist and I do have a record player at home but before I could say “what would happen if…” my plans for experimentation with the record player were blasted out of the water. So I had to make a model record player out of a rotating spice rack. This probably worked better as I could control the speed of rotation, though it did make taking photographs tricky.

record player, turntable
The record player at Red Door

So, what would happen if we put a coffee at the centre of a turntable? The movement of fluids in cups and on record players is extraordinarily complex and is indeed very far from my ‘area of expertise’. However, we can start to understand what might be happening in the cup by making some approximations. Our first approximation is that the coffee in the mug rotates as a ‘rigid body’, meaning that it rotates as a whole. As the coffee cup rotates about its central axis on the “record player” the coffee inside the cup will (eventually) also rotate at the same angular velocity (speed of rotation). The fact that there is a rotation means that there is a force acting on the particles in the coffee liquid. This force produces an acceleration that increases with increasing distance from the axis of rotation. Each coffee particle is of course also subject to the vertical action of gravity. The combined acceleration means that each particle is simultaneously being pulled downwards and inwards. As the acceleration due to rotation increases with increasing radius, the horizontal acceleration becomes increasingly dominant away from the centre of the cup. This leads to the familiar curved surface (a dip at the centre of the mug) that we see with rotating fluids.

vortices, turbulence, coffee cup physics, coffee cup science
This polystyrene cup was rotated about its axis before being stopped. The water inside continues to rotate causing turbulent layers at the edges. These have been visualised with a small amount of blue ink.

Yet we know that this cannot be the full story. If we suddenly stop rotating the mug, the coffee in the mug continues to rotate for a while but does not do so indefinitely; it slows down. We can understand this by refining our approximation that the coffee inside the mug rotates as a rigid body. In fact, the coffee is a viscous liquid and the viscosity means that the layer of coffee immediately adjacent to the mug walls will move at the same speed as those walls: Stationary wall, stationary coffee. The coffee towards the centre of the cup meanwhile continues to rotate for a while. Imagine suddenly stopping the record player so that the mug is now still but the coffee inside continues to spin around the central axis. Stress is being produced between the stationary ‘layers’ of coffee next to the mug wall and neighbouring ‘layers’ of rotating coffee. This stress leads to turbulence. We can make this turbulence visible if, instead of coffee we use a mug of water. Rotate the mug of water as before and then suddenly stop the mug rotating. As with the coffee, the water continues to rotate. Now drop a tiny amount of water soluble ink or food colouring into the very edge of the water (I used a cocktail stick dipped in ink and held against the mug wall so that a small amount dripped into the water). As the water continues to spin, the ink is caught up in the turbulence and the vortices it produces can be seen. These concepts of boundary layers and turbulence are important for many applications including weather systems and car design. We need to understand how liquids (or gases) flow past each other in order to predict the weather and we need to know how they flow past solid objects in order to make cars more aerodynamic. In the coffee however I think that this turbulence is one of those things that is worth just creating and appreciating. A great demonstration of beauty, art and science in a mug of coffee.

Please do share your pictures of these coffee cup vortices if you manage to create them, particularly if you are able to see the effect with cream in coffee. You could either write about your results in the comments section below or email me photographs of your coffee and I will include them on this page. As always, enjoy your coffee.

My thanks to Kate & Edward of Red Door for sending me the photos of Red Door.

Extra photos of vortices in a rotating coffee:

Rotating coffee

An attempt at visualising the vortices using cream in coffee. Not so successful though you can see at least 2 well defined vortices in the top left of the image. Introducing the second liquid right at the edge of the mug seems critical, not so easy with cream as it is with ink!

Categories
Coffee review Home experiments Observations Science history

Joe’s espresso cafe bar, Victoria

radiant heat, heat loss, heat conduction, infra red, Joe's espresso cafe bar
The slightly ajar door at Joe’s espresso cafe

A few weeks ago I happened to be near Joe’s espresso café bar on the corner of Medway St. and Horseferry Road, with around twenty minutes to spare. Joe’s is an old-style independent café, very focused on their lunch menu and take away coffees. Nonetheless, there is a decent sized seating area in a room adjacent to the ‘bar’ where you can sit with your coffee and watch the world go by on Horseferry Road. It is always nice to come across a friendly café that allows you to sit quietly and people-watch. As I sat and watched the taxis pass by, I became aware of the fact that it had got quite cold. The people who had just left the cafe had left the door to the room slightly open; the cold was ‘getting in‘. Now I know, heat goes out, cold does not come in but sitting there in that café that is not how it felt. Then it struck me, rather than cause me to grumble, the slightly open door should remind me  of the experiments of Carl Wilhelm Scheele (1742-1786).

Scheele was a brilliant chemist but one who performed experiments that would make our university health and safety departments jump up and down spitting blood. Recognised for discovering oxygen in the air (Priestley discovered it a few years later but published first), manganese and chlorine, Scheele also investigated arsenic and cyanide based compounds. It is thought that some of these experiments (he described the taste of cyanide) contributed to his early death in May 1786 at the age of 43. Fortunately, none of this has a connection to Joe’s espresso café. What links Scheele with Joe’s, is Scheele’s discovery of ‘radiant heat’ as he was sitting in front of his stove one day.

Open fire, Carl Wilhelm Scheele, Radiant heat, infra red, convection
Sitting in front of a fire we can observe several different ways that heat moves.

Scheele’s house was presumably very cold in winter. He describes how he could sit in front of his stove with the door slightly ajar and feel its heat directly and yet, as he exhaled, the water vapour in his breath condensed into a cloud in the air. The heat from the stove was evidently heating Scheele, but not the air between Scheele and the stove. He additionally noted that this heat travelled in straight lines, horizontally towards him, as if it were light and without producing the refraction of visible light associated with air movement above a hot stove. Nor was a candle flame, placed between Scheele and the stove, affected by the passage of the heat. Clearly this ‘horizontal’ heat was different from the convective heat above the stove. Scheele called this ‘horizontal form’ of heat, ‘radiant heat’.

A few years later, the astronomer and discoverer of Uranus, William Herschel (1738-1822) was investigating glass-filter materials so that he could better observe the Sun. Using a prism to separate white light into its familiar rainbow spectrum, Herschel measured the temperature of the various parts of the spectrum. Surprisingly, the temperature recorded by the thermometer increased as the thermometer was moved from the violet end to the red end of the spectrum and then kept on rising into the invisible region next to the red. We now recognise Herschel’s observation of infra-red light as responsible for the radiant heat seen by Scheele, though a few more experiments were required at the time before this was confirmed.

sunlight induced chemical reactions, milk
Often milk is now supplied in semi-opaque bottles. Why do you think this is?

Further work by William Hyde Wollaston (1766-1828) and, independently Ritter (1776-1810) & Beckmann not only confirmed Herschel’s infra-red/radiant heat observations but also showed that, at the other end of the spectrum was another invisible ‘light’ that produced chemical reactions. Indeed, milk is often sold in semi-opaque plastic containers because of the fact that the taste and nutritional content of the milk are affected by such sunlight induced chemical reactions.

So, it seems to me that, in addition to an interesting story with which to idle away 20 minutes in a café, this set of thoughts offers a variety of experiments that we could try at home. If we are out, we could try to discern the different ways that heat is transferred from one body to another (as Scheele). If we had a prism, we could perhaps repeat Herschel’s experiment very easily with a cheap (but sensitive) thermocouple and, if we were really ambitious hook it up to a Raspberry Pi so that we could map the temperature as a function of wavelength. Finally, we could investigate how light affects chemical reactions by seeing how milk degrades when stored in the dark, direct sunlight or under different wavelengths. If you do any of these experiments please let me know what you discover in the comments section below. In the meanwhile, take time to enjoy your coffee, perhaps noticing how the hot mug is warming your hands.

Books that you may like to read and that were helpful for this piece:

“From Watt to Clausius”, DSL Cardwell, Heinemann Education Books Ltd, 1971

“On Food and Cooking: The science and lore of the kitchen” H McGee, Unwin Hyman Ltd 1986

Apologies to university H&S departments, you guys do a great job (mostly!) in trying to help to prevent us dying from our own experiments too prematurely.

 

Categories
Coffee review Observations Science history

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.

Categories
Coffee review Observations

Arepa and Co, Haggerston

Haggerston Canal
Arepa and Co are on the right hand side of this canal

Edmond Halley (of comet fame) was born in the London district of Haggerston in 1656. More recently, Arepa and Co a Venezuelan cafe located alongside the canal that runs through the district, has just celebrated its first birthday there. This cafe serves a variety of Venezuelan foods including the arepas of the name which are, apparently, a traditional corn cake that can be filled with a variety of fillings (more info here). There are seats both inside the cafe or outside, overlooking the canal. As it was the early afternoon and we’d already had lunch, we decided upon a coffee, a sugar cane lemonade and, to accompany it a plate of Tequenos de Chocolate. These unusual little pancakes filled with chocolate were delightful to enjoy with a cup of coffee and a view over the canal. Sitting back and enjoying this relaxing view, I noticed a tree on the roof of a building on the opposite side of the canal. Hanging on the tree were a number of glass shapes. As the wind blew, the different faces of the shapes caught the Sun. Looking towards these glass shapes, they appeared to change colour as the sunlight was refracted through them. A glinting rainbow array of light fell onto our side of the canal.

The story of the investigation of colour is a great example of how our preconceived ideas can influence the results that we think we see. Up until the seventeenth century, colour was viewed as a property of the surfaces of an object as opposed to “light” which was that which rendered objects visible. Therefore trying to explain how rainbows formed or light scattered from ornaments was a difficult task. Indeed, medieval philosophers (the term ‘scientist’ is a nineteenth century invention), considered that there were only seven colours: Yellow, orange, red, purple, green and black and white.

Prism associated with Isaac Newton
A late C17th prism in the British Museum collection, © Trustees of the British Museum

Work understanding colour as a refracted component of white light started with Marci in his 1648 work Thaumantias (another name for Iris, the Greek goddess of the rainbow) and continued with Newton’s famous experiments with prisms. Newton showed that a glass prism refracted the different colours of light by different amounts (resulting in a spectrum). If two prisms were placed at right angles to each other, the rainbow of light from the first prism recombined into white light emerging from the second. With the change in mindset that this brought about, phenomena such as the rainbow could be more easily explained.

Grecian, Coffee House, London Coffee House
The Devereux pub now stands on the site of the Grecian coffee house, a former meeting place of the Royal Society

Which brings me back to coffee. Back in the eighteenth century cafes (or coffee houses) were not just places to have coffee but places to engage in the latest philosophical, political or scientific discussion and debate. Scientists of the day regularly gave public lectures and demonstrations in coffee houses both as a way of entertainment and of education. One scientist who participated in this was Stephen Demainbray (1710-1782). Demainbray demonstrated Newton’s experiments and theories on colour to a coffee drinking audience. The models that he used to explain the refraction of light are now on display in the Science Museum which is well worth a visit if you are in London. In the present day, there are still cafes and coffee houses that try to do a similar thing (of showing fun science to a coffee drinking audience), although perhaps sadly there are fewer now than there were then. Two movements that are trying to put the science back into coffee houses are Science Cafes and Cafe Scientifique. Although not always held in cafes, both movements have the aim of combining interesting science with a cup of coffee or glass of wine. Somewhat poetically the next Cafe Scientifique in London is to be held, on the 9th December, at the Royal Society. It is poetic because back in the time of Newton, discussions with the Royal Society president (Newton) and other society members took place at the Grecian Coffee House.

Both “Science Cafes” and “Cafe Scientifique” have events worldwide. It is worth taking a look at their websites to see if there is an event near you. Why not pop along and see what you can find out while having a cup of coffee?

 

Sources used:

The Rainbow Bridge, Raymond L Lee, Jr and Alistair B Fraser, Pennsylvania State University Press, 2002

The Nature of Light, Vasco Ronchi, Heinemann, 1970

London Coffee Houses, Bryant Lillywhite, George Allen & Unwin Ltd, 1963