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.

Why is glass transparent?

Sitting at my desk, I can look out onto my backyard through sliding glass doors. So why can I see my backyard at all? That is, why is glass transparent? We take the clearness of glass (and plastics) for granted, but this property is incredibly important. Seeing the birds in my backyard may not be critical, however, seeing oncoming traffic when I'm driving my car is. Allowing light into my home through windows saves the energy required to illuminate my home so I wouldn't walk into things. Think of the deli case at your local supermarket – the glass allows you to see the goodies inside, but protects them from the other customer's germs.

I wrote about the history of glass here, however, the fact that glass is clear likely kept us using it for so long. For example, my house would be a lot more secure from break-ins if I replaced all the glass windows with steel plates. Two physical properties play a role in making something transparent, the object itself and its sub-atomic makeup.

Transparency to visible light is common in the stuff around us -- For example, air and water. In fact, many gases and liquids are transparent because their structure isn't rigid, leaving plenty of room for light to pass through. However, solids don't tend to be transparent because they have a tighter, more orderly structure, making it harder for light to pass through. Glass (and clear plastics) are made by heating their components, mostly silica sand, into liquid form and then allowing it to cool. As a result, glass is rigid like a solid with a random structure like a liquid making it possible for light to pass through.

Light acts both as a wave and a particle. If we consider light as a particle, which is called a photon and contains a certain amount of energy, it can interact with the electrons in the matter around us. When a photon encounters an electron the following may occur:

1.The electron absorbs the photon's energy and vibrates a little faster – that is, the photon's energy has been converted to heat.

2.Again the electron absorbs the photon, but this time it stores the energy and re-emits it later, a phenomenon called luminescence. Think of an analog wrist watch (remember the ones with a two arms and a circle of numbers?). Often the numbers were painted with a substance that would absorb light and glow, allowing you to see the time in the dark.

3.The electron can absorb the photon then re-emit it back in the direction it came from. This is reflection and is why you can see your image in a mirror.

4.Finally, the electron may not be able to absorb the photon at all, so the photon just passes by.

These electron/photon interactions can all occur within a single substance, or some combination of them. If only case 4 occurs, that is the electron's within an object can't absorb a photon in the visible light spectrum, that object will appear transparent. Glass has this property, which is why it makes great windows.

As a tangent, glass absorbs much of the UV spectrum which is why you can't get a tan behind glass.

Time-scales

Working on my final thesis draft has me thinking about time-scales. From our point-of-view time is linear, marching at a constant rate from past to future (unless you are stuck in an extremely dull lecture or on an overcrowded bus crammed beside someone with bad BO – then time seems to slow down to a snail's pace). So, when the conditions are right for something to happen, how long until it does? This isn't so easy to figure out, however, it's relatively easy to figure out the minimum time when that 'something' can happen. For example, my favorite, and apparently everyone else's favorite, coffee goes massively on sale once in a while. When I see the sale in the flier, the conditions are right for cheap coffee. However, I'm at home and the coffee is a short walk away. So, even though the conditions are right, the minimum time I can actually get the coffee is about 15 min later (I've learned this cheap coffee sells out quickly, so I need to go right away). So the coffee time-scale is about 15 min – which is the minimum amount of time until I have the coffee.

Remember the jar experiment?

I've been a bit delinquent about jar experiment updates. I started with a sealed jar full of water from my fish tank here. It has been sitting on my desk ever since. A long time passed until anything grew. Now there appears to be two types of algae, a forest green scum on the sides (which can be seen in the picture) and something thick and black along the bottom. I must admit, I don't feel inspired to open the jar as I fear what it might smell like.

April Showers

It's another 'April Showers' type day today – rain has been coming down all day with no signs of stopping. Worms are making their way onto the roads and side walks to the delight of the robins (who don't need to get up early to get a worm around here). I like worms, they represent healthy soil to me. Since I'm someone who is trying to grow tasty food in my back yard (step 1: grow vegetables, step 2: save planet), healthy soil is a good thing. I agree with what Charles Darwin said about worms:

“It may be doubted whether there are many other animals which have played so important a part in the history of the world as have these lowly organized creatures.”

When I lived in various apartments, I tried indoor worm composters (always of my own construction). Generally, my worms did well but, so did fruit flies. I tried at least three times, each time abandoning the idea because of the fruit fly swarms that emerged. Maybe there was some trick I needed to know about, but now that I have outside space for a proper compost, I'm not going to worry about it.

There are all sorts of different types of worms but, the common earthworm or Lumbricus terrestis is the one I see in my garden. These guys usually hang out in burrows close to the surface and recycle organic debris. Leaves, grass clippings, even carrot peels can all be turned into great soil by worms. Their bodies are divided into linked, somewhat independent segments. Each segment is pressurized with fluid to give the worm shape and has muscles that can act independently to allow it to move. The mouth is at one end and along the whole body is the gut and waste is pushed out the other end. This waste (that is, poo) is what makes good soil.

Let me be clear... a bit about glass

I found a photo I took of a rainbow last summer when we drove across Canada. I took it from a moving car (I wasn't driving) - so it isn't as fantastic as it could be.

I've been thinking about Theodoric of Freiberg's rainbow experiment (I wrote initially about it here). He used a spherical glass filled with water to approximate a rain drop and a piece of parchment with a pin hole in it. By shining light through the parchment hole and onto the glass sphere, he was able to observe the result of raising and lowering the sphere. From this he explained all the colours of a rainbow. So his glass sphere must have been essentially perfect for this to work, and he wasn't the only one using these sphere's for optics experiments. So how did we get so good at making glass? (the extremely short version)

Glass making is an old art, by about 1500 BC the Egyptians were making glass vessels and soon after the Phoenicians mastered the art and began exporting glass goods all over. However, the Romans with glass blowing (likely invented by the Phoenicians), put cheap glass vessels into their citizen's homes. Romans went on to adapt glassblowing for making glass windows for some of their buildings – not widely done because they lived in a warm environment. Roman windows were made by blowing glass into a bulb shape, then manipulating it into a cylinder shape. The cylinder was split open lengthwise before being re-heated and forced flat. One of the largest windows made of this method was found in Pompeii measuring just over a metre wide.

So, the Romans weren't hugely into glass windows, but after they were gone, those who lived to the north took up interest in them. The technique used became simplified to blowing glass into spheres and then cutting them while still hot into the shallow bowls of 'crown-glass' windows. Additives of different minerals result in brilliant colours for stain glass windows. Since, churches were one of the few places rich enough to afford glass windows and they wanted to tell stories through cut coloured glass put back together, large sheets of uniform glass wasn't necessary.

Throughout medieval times, rich folks were drinking out of blown glass and keeping the weather at bay with blown glass windows. So by, Theodoric's time in the fourteenth century, glassblowing had been around a long time. If an artisan can make a nice wine glass, certainly that skill could be put to use for scientific instruments.