Playing with fire

candle

A candle on earth

I remember making candles when I was a kid. We filled empty food cans with paraffin wax – the stuff that comes as a opaque block about the size of a deck of cards. The cans were then put into a bath of boiling water until all the wax melted. A few crayon stubs were added to each can, creating an array of colours. I tied a thick piece of cotton string, destined to be the wick, around a pencil for easy dipping.

Next, dipping (the messy part) could begin. With each dip another layer of wax clung to what was already there, increasing the diameter of the candle-to-be. I rotated through the colours, creating what must have been gaudy candles. When the candle was thick enough to stand on its own, the fun part began: we could light them.

A flaming match held to the exposed end of the wick has enough heat to vaporize wax within the wick and react with the oxygen in the air. Within moments a teardrop-shaped yellow flame flickers to life. The heat from the candle’s flame melts the wax, and the melted wax is drawn up by the wick, sustaining the flame. At its hottest, a candle’s flame can reach 1400 degrees Celsius.

Heat vaporizes the wax creating a gaseous cloud where combustion takes place. Combustion is a series of chemical reactions converting molecules into new combinations – an inefficient process resulting in heat and light. Light, along with its cousin heat, signify the release of excess energy.

Compared to an incandescent light bulb, a candle produces 100 time less light, which is probably why candles are now mostly used to set moods, conduct rituals and provide light in power outages. I don’t often light candles, after all they are one of the leading causes of residential fires and they put soot and chemicals into the air I breathe. But, when I do have a reason to light a candle, I enjoy watching the flickering flame – I find something about it quite mesmerizing.

In my mundane earth existence, when I light a candle the hot gases formed are less dense than the air around them, and so they rise in a process of natural convection into the familiar teardrop shape. This natural convection hinders complete combustion, so soot forms which makes the flame yellow.

Out in my funky futuristic (imaginary) spaceship, where there would be no gravity, natural convection wouldn’t occur, and I would get a perfectly spherical flame. And, the flame would require ventilation or it would smother itself as its temperature would be evenly distributed. (here’s a good, but slightly inaccurate video) On the plus side, the combustion would be complete – so soot would not form. The flame would be bluer and more efficient.

Another effect of gravity on a candle’s flame is the flickering. The frequency squared of a flame’s flickering is proportional to the force of gravity over the diameter of the candle. Meaning that a candle with a smaller diameter would flicker at a faster rate than one with a larger diameter. So a candle on another planet (with different gravity) would flicker at a different rate than the same candle on earth.

A candle on my spaceship wouldn’t flicker at all (I would have to be mesmerized by its pretty spherical blueness instead).

note – this post was originally published back in May 2010 (here)

another note – I downloaded the image from here

Playing with fire – again

Burning an old bird house

We partly heat our home with wood for reasons including having a fireplace, being given a large quantity of well seasoned firewood and taking down a tree down on our lot. Ours is an actual fireplace (not a wood stove), that is only a chimney modification away from an ancient fire pit – meaning that if we aren’t careful our house fills with smoke, which I consider a negative point. On the plus side, having a fireplace means there is always kindling around making me ready for a vampire attack.

The sound and smell of wood fires are nostalgic for me. A whiff of wood smoke transports me back to the house I grew up in and the wood stove that heated it (funny, I don’t immediately recall carrying all that wood into the house – yet I did lots of that too). We aren’t alone with our fireplace as 20% of Canadians partly heat with wood.

In general, wood is a much better heating source than fossil fuels. For example, natural gas emits 15 times more carbon dioxide per kilogram than wood. Is a wood fire better for the environment than using electric heat (our other option)? The type of wood burned matters in two ways. First, the energy content of wood depends on the variety of tree it came from. Secondly, how dry the wood is. Moisture content determines how firewood burns and how much heat is released. Dry wood produces more heat than green wood of the same species.

Here is a good explanation of why wood might be okay (from here):

Only a relatively small percentage of electricity is from renewables like hydroelectric dams, and even then there are environmental problems due to flooding large areas. Wind turbines will never produce enough electricity to be used widely for home heating.

Firewood, on the other hand, can be produced with slight environmental impact because it needs little processing and most of it is used close to where the trees grew. Wood is the most economical and accessible of all renewable energy resources for many households and it has value beyond the displacement of fossil fuels and reduction of greenhouse gas emissions. It is practiced on a small scale and the householders that use it gain a better understanding of their impacts on the environment than users of other energy sources. Families who heat their homes with wood responsibly should be recognized for their contribution to a reduction in greenhouse gas emissions and a sustainable energy future.

In a modern context, and knowing what we now know about the environmental impacts of all energy use, wood can be thought of as a ‘new’ energy resource, provided it comes from sustainable sources and is burned in advanced combustion appliances.

The article goes on to make it clear that wood heating isn’t for everyone and how it’s done is critically important.

An interesting side point – if a truck load of wood spills, it can just be picked up again the only cost is a bit of labour. If a truck load of oil spills it’s a whole different problem. Plus, where I live wood can come from near by, while fossil fuels come from far away.

A sappy story

Last weekend we took a jar of used turpentine to our recycling center to be disposed of. The jar’s lid wasn’t on perfectly, the jar tipped as I drove around a curve, and a tiny splash of turpentine spilled, filling the car with a sent reminiscent of a pile of fir branches. The smell took me back to when I was a kid exploring the forest. Fir trees are sappy – a fact I learned early while climbing them. The fir trunk has sap blisters that burst under my hands when I grabbed the branches. The sap left sticky residue on my hands, so climbing a fir tree quickly became a inferior choice compared to the maples and alders. But, something about the sap intrigued me, so I would collect it by lancing the blisters with my pocket knife and capturing the drips in a large clam shell. When I had enough, I would light the sap to see the black smoke (probably not the smartest of ideas).

The smell of turpentine started me wondering if it’s made from fir sap. It didn’t take much digging to learn that what I’m calling sap is actually resin, a hydrocarbon secreted by predominantly coniferous trees and a few other plants (both the biblical frankincense and myrrh are resins). Resin is also known as pitch and it has some neat properties. It behaves as a solid normally, but if a force is imposed on it long enough the deformation will increase indefinitely, just like a liquid. Cool, but how does it become turpentine?

Resin is converted to turpentine by distillation, a process where the parts of a liquid are separated using heat – for example if you want to make a fortified wine like brandy, you would need to heat the wine and collect the alcohol as it evaporated away. Generally, turpentine is made from pine trees, but it’s also a byproduct from reducing coniferous trees to pulp.

Turpentine is commonly used as a solvent; we use it for cleaning brushes coated in oil paints. It could also be used to thin out oil paints.

As a tangent, I pulled out an old country skills handbook to see what they suggested one could do with turpentine. Apparently, it was used as an ingredient in mosquito repellent along with some other nasty stuff – I was relieved to see that this concoction was to be used by saturating cloth with it and placing it by the door instead of putting in on your skin.

More on candles

‘There is no better, there is no more open door which you can enter into the study of natural philosophy than by considering the physical phenomenon of a candle’

– Michael Faraday (1791-1867)

Faraday was a physicist and chemist, best known for his contributions in the areas of electricity and magnetism. Two units of measures are named for him: the Faraday (unit of electrical charge) and the Farad (unit of electrical capacitance). Faraday also spent time on projects such as lighthouse construction and operation, and protecting metal ship hulls from corrosion. He gave tips on the cleaning and protection of artwork. On top of these and other activities, he delivered a series of public lectures and wrote for the general public. Around 1860, Faraday gave a successful series of lectures on the chemistry and physics of flames called ‘The Chemical History of a Candle‘, a transcript of which I stumbled upon recently.

On describing a method of making candles, he explained: ‘The fat or tallow is first boiled with quick-lime and made into soap, and then the soap is decomposed by sulphuric acid, which takes away the lime, and leaves the fat rearranged as stearic acid, while a quantity of Glycern is produced at the same time … The oil is then pressed out … and at last you have left that substance which is melted and cast into candles’

Makes me tired just reading that! Candles can also be made by the dip method I’ve described before or from bees wax. In Faraday’s day sperm candles were made from purified oil found within the head cavities of sperm whales and paraffin candles were made from paraffin somehow obtained from bogs in Ireland (how exactly this was done was not mentioned – I’m curious so I may look this up later).

A burning candle is a chemical reaction that turns wax and oxygen into carbon dioxide and water while letting off heat and light. Soot isn’t a product of this chemical reaction, instead it is incompletely burned carbon. Once lit, how does a candle get fuel to sustain itself?

The heat of the flame melts a pool of wax. This wax is then drawn to the flame by capillary action – the wick just provides a way to get wax to flame. Capillary action is a process where liquid can rise, seemingly against the force of gravity, and it is common in the world around us. For example, the transport of fluids in plants uses capillary action. If you were to put a freshly cut celery stick into a cup of water that had purple food colouring in it, you would end up with purple celery. Capillary action occurs in thin tubes or within the weave of a candlewick as a result of inter-molecular attractive forces between the liquid and solid surrounding surfaces.

Molecules within a liquid are attracted to one another, this is called cohesion, which manifests as surface tension. Because of cohesion, the most efficient shape for a liquid is a sphere, which is why raindrops are round. When a liquid touches a solid material (like the wick) that attraction now occurs with the solid material – this is called adhesion. If adhesion is greater than cohesion the surface will curve up at the boundary like the meniscus formed when water is in a glass. Alternatively, if the adhesion is less than cohesion, then the surface will curve down. So, if the cohesion of water molecules and adhesion to a solid surface act together (which would happen in a thin space) the liquid would be drawn up – the thinner the space, the higher the liquid would rise. And that’s how wax gets to the flame.

By the way, Faraday’s idea of using a common thing like a candle flame to teach science is still used.

Playing With Fire

I remember making candles when I was a kid. We filled empty and cleaned food cans with paraffin wax – the stuff that comes as a opaque block about the size of a deck of cards. The cans were then put into a bath of boiling water until all the wax melted. A few crayon stubs were added to each can, creating an array of colours. I tied a thick piece of cotton string, destined to be the wick, around a pencil for easy dipping. Next, I started dipping. With each dip another layer of wax clung to what was already there, increasing the diameter of the candle-to-be. I rotated through the colours, creating what must have been gaudy candles. When the candle was thick enough to stand on its own, the fun part began: we could light them.

A flaming match held to the exposed end of the wick has enough heat to vaporise wax within the wick and react with the oxygen in the air. Within moments a teardrop-shaped yellow flame flickers to life. The heat from the candle’s flame melts the wax, and the melted wax is drawn up by the wick, sustaining the flame. At its hottest, a candle’s flame can reach 1400 degrees Celsius. What is actually happening? Heat vaporizes the wax creating a gaseous cloud where the combustion takes place. Combustion is a series of chemical changes that converts molecules into new combinations – however this process isn’t totally efficient resulting in the production of heat and light. Light, along with its cousin heat, are part of the electromagnetic spectrum and signify the release of excess energy.

Candles used to be one of the main ways to create artificial light. However, compared to an incandescent light bulb, a candle produces 100 time less light, which is probably why candles are now mostly used to set moods, conduct rituals and provide light in power outages. I don’t often light candles, after all they are one of the leading causes of residential fires and they put soot and chemicals into the air I breathe. Some candle shops are so over-scented I can’t even stand being in them: I can’t imagine what my house would smell like if I burned their candles! But, when I do have a reason to light a candle, I enjoy watching the flickering flame – I find something about it quite mesmerizing.

One of the discoveries from experiments conduced in space is the importance gravity has in the formation of a flame. Here, in my mundane earth existence, when I light a candle the hot gases formed are less dense than the air around them, and so they rise in a process of natural convection into the familiar teardrop shape. This natural convection hinders complete combustion, so soot forms which makes the flame yellow. Out in my funky futuristic spaceship, where there would be no gravity (unlike the spaceships on TV), natural convection wouldn’t occur, and I would get a perfectly spherical flame. In space, my flame would require ventilation or it would smother itself. Its temperature would be evenly distributed and combustion would be complete, so soot would not form. The flame would be bluer and more efficient.

Another effect of gravity on a candle’s flame is the flickering. The frequency squared of a flame’s flickering is proportional to the force of gravity over the diameter of the candle. Meaning that a candle with a smaller diameter would flicker at a faster rate than one with a larger diameter. So a candle on another planet (with different gravity) would flicker at a different rate than the same candle on earth. A candle on my spaceship wouldn’t flicker at all (I would have to be mesmerized by its pretty spherical blueness instead).