If you went back in time, what could you teach this civilization?

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How hot does a typical campfire get? Is it hot enough to melt silver?

This government publication on the thermal performance of masonry chimneys and fireplaces didn’t find temperatures greater than 855°C and that was the gas temperature in the flu.  This test of a rocket stove found a maximum average temperature of 945°C and a max temperature of 1049 °C. The third paper found that for small flames (less than about 1 m base diameter), continuous flame region temperatures of around 900°C should be expected. For large pools, the latter value can rise to 1100~1200°C.


True or False: Concrete can be made by mixing powdered limestone, sand, gravel and water?

Interesting use of concrete for construction  (source: seier+seier)
The Pilgrimage Church by Gottfried Bohm was opened in 1962 in Neviges Germany

Concrete is the most often used construction material of the modern world.  It is simple and economic to make and if the Egyptians had known the secret they could have made it 4000 years ago. To make concrete, first you need to make the cement (or mortar) that holds the concrete together. 

The Romans did this by burning limestone (which is mostly calcium carbonate CaCO3) to create something called quick lime (calcium oxide CaO). Burning isn't quite the right term because "to burn" usually indicates an oxidation process which involves the "chemical union of oxygen with any substance".  What actually happens in a lime kiln is that the temperature of the limestone is increased to a point above its dissociation temperature.  The earliest lime kilns were really just layers of wood and limestone stacked together and lit like a giant bonfire.  So it is easy to see why it is called burning limestone when it really isn't.

Land Navigation - A comprehensive guide

Navigation isn't about getting lost and then trying to figure out where you are.  (Although sometimes that happens.)

image of map and compass

Navigation is about systematically using the tools at hand to track your location and to plan a route to your destination. Thus your brain is your most important navigational tool.

I was never happy with all of the books, videos and websites available to teach navigation so I created  this guide to cover the basics of each of the principle tools of navigation - map, compass, and GPS unit.

You don't have to read them in order but it  will make more sense if you do.


On a boat in cold water? - You should know these 5 things

1. You better be wearing a life jacket before you end up in the water.

The gasp reflex in action   (source: 3Nues)
Woman gasping in cold water

Cold water forces a rapid, uncontrollable gasping in everyone and that lasts from 1-3 minutes. If you happen to gasp while your mouth is underwater, you will draw the cold water into your windpipe and lungs which can then spasm and contract. Even if you manage to get your mouth above water, you may still not be able to clear the water and get enough oxygen. If things go really wrong, your epiglottis may spasm closed and you will dry drown. (The epiglottis is the cartilage flap that  keeps liquid out of your lungs when you drink.)  

There is some evidence that keeping the cold water off your face and head may lessen the gasp reflex. That is why you want the life jacket on before you hit the water. It helps to keep your face and mouth out of the water. The initial immersion in cold water causes a sudden constriction of surface blood vessels which causes an immediate jump in blood pressure and heart rate; sometimes to maximum heart rate. If your heart cannot handle this jump, it stops and you die. This seldom happens in healthy and fit people but the danger is still there. If you have a choice, make sure to wear a life jacket that is self-righting so that it keeps your face out of the water if you are unconscious....

Five ways to find north if you don't have a compass

A decent compass is so inexpensive that everyone should own one.  But if for some reason you find yourself trying to locate north without a compass,  here are some techniques to get you pointed in the right direction.  I've organized them from most accurate to least accurate.  If two methods are equally accurate, then I have listed the easier one first.

1.) Locate the North Star.  This method will accurately show you true north but it only works at night , in the Northern Hemisphere and when you have a clear view of the sky.

(How to find The North Star - Click for larger image)
Finding Polaris


The North Star (also known as Polaris) is almost directly above the North Pole.  It is not the brightest star in the sky.  It appears to be about as bright as the two pointer stars in the Big Dipper.   Just follow the pointer stars and at about 5 times the distance between the two pointer stars you will find the North Star.  How high the North Star is in the sky depends upon your latitude.  If you are in Northern Alaska,  the North Star will appear almost over head.  If you are in the Florida Keys, the North Star will be much closer to the horizon.



Need to secure your home on a budget?

Source: epicture
Front Door

You don't need to spend lots of money to feel more secure in your home but you do need to have a plan. Most homeowners put little or no thought into home security and, as a result, the thieves benefit. With some observation and careful thought you can create a plan that makes thieves skip your house and move on to something easier. 

The plan starts with the realization that there is no such thing as absolute security. The goal isn't to turn your home an impenetrable fortress. (Although there is something romantic about the idea of living in a castle with a moat.)  The goal is to make your home  an unattractive target for thieves.   This can be done without turning your home into a prison compound or breaking your budget.



Fresh water is essential to civilization

Water is absolutely essential to life1. In survival situations, there is something known as The Rule of Threes.  It says that you can survive 3 minutes without air, 3 hours in inclement weather, 3 days without water, 3 weeks without food.  We are going to assume that you don't  have to worry about air to breathe or freezing to death as you begin your journey from hatchet in the woods to sending an email.  That makes finding fresh water your highest priority.  Nile as seen from space at night

It's no wonder that the first great civilizations emerged alongside freshwater rivers such as the Nile, the Tigris, the Euphrates, the Indus and the Yangtze. These fresh water sources provided the large quantity of water needed for farming.  You can clearly see the Nile from space at night. (Click on the image at right for a larger view) 

Let's start with the basics.  You need to know:

  1. Where fresh water comes from
  2. How you find it
  3. How to collect and store it
  4. How to treat it
  5. How much you are going to need for personal use or farming.
  6. Interesting facts about water (surprisingly important)

What is the most efficient form of transportation in the world?

(Click for a larger image)
Chart of motive efficiency

The humble bicycle is an amazingly efficient form of transportation.  I would have liked to see mass transit such as trains on this list. I wonder how they would compare.  

Where fresh water comes from

Fresh water is scarce

Even though the Earth’s surface is 70% water, 97% of it is salt water. Of the 3% that is fresh water, all but about 1% is locked up in ice at the poles. That means only 1% of the water on Earth is really useful to humans. That makes fresh water a relatively scarce resource1. To put that in another perspective: Imagine if you could only use 1% of the money in your wallet.  What could you buy with that?  

Image of the hydrologic cycle

It literally comes from the sky

The hydrologic cycle describes how fresh water is created by the sun. The heat from the sun causes the water of the surface of the Earth to evaporate.  When the water evaporates it leaves behind the salt and other minerals that it had in it.  When it condenses again and falls to the Earth (in the form of precipitation), it is fresh water.  It will either drain back to the ocean or be evaporated again.  This cycle just keeps repeating.

1The English word ‘rivals’ comes from the Latin word rīvalis , which literally means : one who shares the same brook.  The notion being that neighbors compete for a precious resource.  



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