Extraction of Lead

LEAD

Lead (symbol is Pb) is a heavy but soft metal, it is reactive with oxygen, which makes the lead look dull. Lead is not a very good conductor of heat, sound or electricity. Lead is found in the Earth's crust and is most commonly a compound of:

• galena (lead sulfide - symbol PbS);
• anglesite (lead sulfate - symbol PbSO4);
• cerassite (lead carbonate - symbol PbCO3);
• mimetite.

Lead can be easily cut, bent and worked to make different shapes. Leads melting point in 621.3 degrees Fahrenheit or 327.4 degrees Celsius and has a boiling point of 3180 degrees Fahrenheit or 1749 degrees Celsius.

Lead is extracted from its ores (ores are rocks that contain metals naturally) this is done by converting the ores to lead oxide and then heating the alloys (alloys is lead mixed with another element) with charcoal. This does not produce pure lead but can be refined further electrolytically. Alloys are harder than pure metals because the different sized atoms distort the normal arrangement of atoms, which makes the layers more difficult to slide over each other.

There are many sources of lead, some more commonly known such as paint, batteries and radiators but also some less commonly known such as children's toys and jewellery (especially the inexpensive children's jewellery sold in vending machines) and imported food.

Bibliography
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/rockd/metalsrev7.shtml
http://www.enotes.com/lead-reference/lead-177335
http://www.health.ny.gov/environmental/lead/sources.htm

By Amy Spencer

Fire Temperature

By Jack Scott

For our practical demonstration, we will be attempting to melt and extract metals. But in order to do this, our fire is going to have to be rather warm in order bring about any sort of change. This poses the question; how can you gauge the temperature of a small woodland fire?

Through logical thinking we could work out a rough temperature by testing what our fire does and doesn't affect. For example, we know that the boiling temperature of water is 100°C. Therefore if water boils over the fire we know that it must be at least that temperature in the heart of the fire. Using this method, we could do a similar test on our popcorn. As Lauren highlighted, "when the popcorn is heated to around 450˚F [approx. 232°C], the moisture in the kernel turns into steam, creating pressure within". So if our corn 'pops' we know we've reached a temperature of at least 232ºC. We could carry on in this fashion, trying different metals (tin, zinc and, aluminium) with different melting points (232ºC, 419.5ºC, and 660ºC) until we find the point at which the fire no longer has an affect(1). But this method is rather long winded and only gives an approximate temperature range.

For a more accurate reading, we could use an infrared (IR) or laser thermometer (these two types of thermometer are basically the same, the laser is just there to make the thermometer easier to aim). IR thermometers work by measuring the amount of infrared energy given off by objects. Molecules are always vibrating constantly; the hotter the molecule is, the faster it vibrates, creating infrared energy. To display the temperature, the thermometer must convert the infrared energy it measures into an electrical signal, which is then converted into a temperature(2). This form of thermometer is now incredibly widespread (you can get them for about £35 on Amazon) as it allows accurate readings in hard to reach and hazardous places.

More 'Spy School' than Forest School

Whilst IR thermometers would probably offer the easiest and most accurate reading, it doesn't really feel natural in our Forest School setting. It would be like like using blowtorches and Vaseline to light our fires instead of the natural resources presented by the constantly-under-the-weather wood trolls.

Another possible method takes advantage of the way that some metal alloys vary in resistance to electrical current depending on their temperature. These "thermistors" can be used to directly measure the temperature of a flame. They are set into the end of a probe and form a circuit which contains a battery and voltmeter. The resistance changes with the temperature and this decreases the voltage in the circuit. The voltage is then multiplied by a conversion factor and is read as temperature(3). Although not strictly an 'au naturale' organic technique, this method does however promote a sense of experimentation and inquiry which is at the heart of the Forest School ethos.

Due to the nature of our demonstration, it probably isn't essential that we have exact measurements of temperature. After all, if we test the temperature by melting different metals, we've kind of completed our experiment already. But, if we needed to, we could now gather accurate measurements and understand how the different technologies work.




(1) http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html
(2) http://www.ehow.com/how-does_4962575_laser-thermometers-work.html
(3) http://forums.govteen.com/science-forum/362173-how-measure-fire.html

Popcorn

Popcorn

A bit about popcorn

Popcorn is a cereal grain, and originates from wild grass. Its scientific name is Zea mays everta, and it is the only type of corn to pop. Popcorn is made up of three main components; the endosperm – the yellow/white carbohydrate made up of soft and hard starch granules, providing energy for the germ. The germ, which is the living part of the kernel, and the pericarp (the hull), which is white/yellow and made of cellulose. Although, it can be red, black, or many colours in between. (1)

Europeans discovered popcorn from Native Americans. Popcorn used to be worn as headdresses and necklaces. It was then used as a common breakfast, served with cream or milk. Popcorn was very common in the United States from the late 19^th century to the mid-20^th century. (2) Native American tribes flavoured popcorn with dried herbs and spices. They also made popcorn soup and beer. (5) During World War Two, Americans ate three times as much popcorn as they had before. (2)

Popcorn is actually good for you. It is a whole-grain, so it provides you with fibre. It provides energy-producing complex carbohydrates. Popcorn is naturally low in fats and calories. It is sugar free, and contains no artificial additives or preservatives. (1)

How old is popcorn?

It is not clear exactly how old popcorn is. Archaeologists have discovered that popcorn has been around long before Europeans arrived in the New World. An 80,000 year old fossil corn pollen was found 200 feet below Mexico City. Researchers discovered 1000-year-old grains of popcorn on the east coast of Peru, so well preserved that they still popped. Popcorn has been found in caves of Central New Mexico that, according to radio-carbon tests, is nearly 5,600 years old. (1)

Popcorn hybrids

There are around twenty-five varieties of popcorn that occur naturally. The popcorn industries are trying to find hybrids with desirable properties, such as ‘popability’. (6)

Why does popcorn pop?

                                                                              (6)


‘Why does popcorn pop?’ is a fascinating question that I was unable to answer without research. People are fascinated by popcorn. Some Native Americans thought that a spirit lived inside each kernel of popcorn, and that when popcorn was heated, the spirit would grow angry and burst out of its home into the air as steam.
After doing some research, it seems that, although less charming, a more scientific explanation exists as to why popcorn pops. (1) Each kernel contains some water, stored inside a circle of soft starch, inside the hard outer casting. When the popcorn is heated to around 450˚F, the moisture in the kernel turns into steam, creating pressure within. As the pressure builds, the casing (the hull) bursts, and the kernel explodes, releasing the water as steam, and turning the kernel inside out. (3) The starch turns gelatinous whilst being heated, and when the hull bursts, the starch spills out and cools to around 40 times its original size. ‘All hull breaks loose.’ This creates the fluffy white popcorn.

The ideal popcorn kernel contains around 14% moisture. If it is much drier, it will not pop, therefore, popcorn kernels should be kept in a sealed jar to avoid the kernels drying out. (2) At harvesting, popcorn has moisture content of 16-20%, which is too high, as the popcorn may spoil once stored. To bring the moisture content down to 14%, the popcorn is conditioned in giant vents, pumping warm air up through it to accelerate the drying. (4)

                                                                             (1)

Click on the hyperlink to see popcorn popping in slow motion. http://www.popcorn.org/ForTeachers/TeachingGuide/PopVideos/tabid/89/Default.aspx (1)

You can pop popcorn by putting it in the microwave, heating it over a stove with some oil, or heating it over a fire (as we did in the forest): 

You can then add whatever topping you like to the popcorn and enjoy the low calorie snack!

By Lauren Watmough

(1)    http://www.popcorn.org/ForTeachers/TeachingGuide/WhatMakesPopcornPop/tabid/88/Default.aspx

(2)   http://www.factmonster.com/spot/popcorn1.html

(3)    http://www.nasa.gov/audience/forkids/home/popcorn.html

(4)    https://www.youtube.com/watch?v=rIldiPSZff

(5)    http://www.knowledgebase-script.com/demo/article-551.html

(6)    http://www.scienceworld.ca/swog/what-makes-popcorn-pop

"And then one day someone discovered how to make fire. Do you realise what that actually means? Can you do it? Not with matches, because they didn't exist. But by rubbing two sticks together until they become so hot that in the end they catch fire. Have a go and the you'll see how hard it is!"

- E.H. Gombrich, 1935, p. 7

Gombrich, E. H. (1935) A Little History of the World. London: Yale University Press.

The Science of Fire

By Jack Scott

It is often argued that fire is one of the (if not THE) greatest and most influential discoveries of Mankind. Without the ability to summon and control the fickle nature of fire, our species, society, and surroundings would be unimaginably alien to what we perceive today. Over time, Man's experiences and relationship with fire have developed to the point where, despite making numerous appearances in many of history's milestones, in our current day to day lives we now rarely interact with this once essential element (in the Ancient Greek sense of the word). One could argue that thousands of years of manipulation and understanding has allowed our society to control and exploit the useful aspects of fire as well as providing safer substitutes to use in our everyday lives.

But, how much more has our knowledge grown since the times when this natural phenomenon would have been explained by fire-spirits and magic? We can all recognise the external characteristics of fire; we know that it produces light, that it burns most materials, and that it is useful for toasting marshmallows. We may also understand that in order to create fire, the components heat, fuel, and oxygen must be brought together in the correct mixture. But apart from that, could you now, categorically and simply explain what fire exactly is? "Well, it's a chemical reaction isn't it...?" was about as far as I got.

With a bit of further investigation, I was able to elaborate on my rather weak initial description. These were my findings. Fire is the visible effect of the process of combustion – a special type of chemical reaction. It occurs between oxygen in the air and some sort of fuel. The fuel must be heated to its ignition temperature for combustion to occur. The reaction will keep going as long as there is enough heat, fuel and oxygen - which is known as the fire triangle.

(1)

Fuels can be solids, liquids or gases. During the chemical reaction that produces fire, fuel is heated to such an extent that (if not already a gas) it releases gases from its surface. When these gases are hot enough, the molecules in the gases break apart and fragments of molecules rejoin with oxygen from the air to make new product molecules – water molecules (H2O) and carbon dioxide molecules (CO2) (and other products if burning is not complete).

In the case of troll bogeys, the sneezes of Southern Wood Trolls contain a mixture of hydrocarbons, which have a melting point usually within a few degrees of human body temperature, which is approximately 37 °C.(2) This low melting point means that troll mucus has a much lower ignition temperature than similar forms of snot. However, it is flammable only when heated to liquid, then the fumes will light, not the liquid itself, so a wick material like leaves, bark, or small twigs is needed to light petroleum jelly bogeys.

(1)

The heat generated by the reaction is what sustains the fire. The heat of the flame will keep remaining fuel at ignition temperature. The flame ignites gases being emitted, and the fire spreads. As long as there is enough fuel and oxygen, the fire keeps burning.

Fuel + oxygen (from the air) = combustion products (mainly CO2 + O2) + heat energy.

The mesmerising flicker of flames often masks the truly astounding science which most of us see but fail to comprehend. Once you are able to understand the intricate reactions taking place at a molecular level, the science of fire becomes a mind-boggling phenomenon - one that we now take for granted. With an increasing amount of detachment between our highly developed species and this ancient metamorphosing element, are we heading towards a time when we forget to acknowledge the unequivocal role that fire played in the history of our planet?


(1) http://www.sciencelearn.org.nz/Contexts/Fire/Science-Ideas-and-Concepts/What-is-fire
(2) www.vaseline.com

Homo heidelbergensis

Homo heidelbergensis.

Homo heidelbergensis is a species of early human that evolved at least 600,000 years ago. They spread across Africa, Asia and Europe hunting large animals and using simple stone tools before disappearing 250,000 years ago (2).

 How They Looked.

These early humans were physically similar to us in many ways being on average only slightly smaller than modern man. The real difference comes from the size and shape of the head. Facially a large forehead and low brow ridges combined with a small chin gave an unmistakably different look. Their elongated heads also resulted in a brain just 10% smaller than ours (1).

A reconstruction from the Natural History Museum (2)

Not so similar right?

 

 

How They Lived.

Evidence for the lifestyle lived by these early humans comes from two main sources, the tools they made and the bones they left behind. These bones however are not all humanoid. At Boxgrove near Chichester a heidelbergensis shin bone, many animal bones and stone tools have been discovered. The evidence here indicates that Homo heidelbergensis was a skilled hunter. Cut marks from hand axes on the bones are overlaid by the tooth marks of scavenging carnivores. This indicates that these early 'humans' were able to kill and butcher their prey without interruption from other dangerous predators such and wolves (4). In order to kill and butcher their food our ancestors would have used flint handaxes such as the example below. By flaking off excess stone a razor sharp edge would be produced.

Now known as Boxgrove man, the shin bone was found at the base of a chalk cliff that would, at the time of his death, have been right on the coast, a nearby stream would have provided fresh water and attracted animals to this site (3).

A Hand axe from Boxgrove (3)

Our Ancestors?

DNA evidence has shown that Humans and another of our early competetors, Neanderthals, had a common ancestor based 400,000 years ago. This means that both species evolved from the same source. Many scientists believe this ancestor could have been Homo heidelbergensis (2). However the widely dispersed population of heidelbergensis, and the differing climates of these habitats, means that Homo sapiens and Homo neanderthalensis evolved in very distinct locations, Neanderthals in Europe and Humans in Africa (5).

By Rob Jones

1: http://anthro.palomar.edu/homo2/mod_homo_1.htm

2: (http://www.nhm.ac.uk/nature-online/life/human-origins/early-human-family/homo-heidelbergensis/index.html)

3: http://www.archaeology.co.uk/specials/the-timeline-of-britain/boxgrove.htm

4: http://www.bbc.co.uk/sn/prehistoric_life/human/human_evolution/first_europeans1.shtml

5: http://www.bbc.co.uk/sn/tvradio/programmes/horizon/neanderthal_prog_summary.shtml