Malak El Khalkhali
12/18/15
Section B
Lit Review
Introduction
A large percentage of the world’s population does not have access to electricity, resulting
in a lack of refrigeration. In the third world countries, 79 percent of the population suffers from
paucity in electricity. One-fourth of the population, as a whole, does not have access to
electricity. The countries suffering the most are located in Southern Asia and Africa. In these
locations, 90% of the population suffers from a dearth of power (Gronewold).
There is an alarming percentage of the population that is suffering from the consequences
of a power shortage leading to their death. Without electricity, food becomes inedible because of
the lack of refrigeration. It is necessary for these regions to get access to refrigeration. They need
a cheap and innovative product that can provide cooling for food storage and protection.
The Need for Refrigeration
People worldwide are suffering from hunger. One of the leading reasons for this is a lack
of refrigeration due to the lack of available of electricity. Without refrigeration, food quickly
becomes inedible. One fifth of the people who experience this problem live in underprivileged
areas with no amenities. It is necessary for these regions to get access to refrigeration. They need
a cheap and innovative product that can provide cooling for food storage and protection. This
solution would have to protect the food from dirt, insects, and high temperatures (Augustin,
2011).
The apparatus does not only need to be used in under-developed countries; it can also be
used as an alternative to preserve fruits and vegetables in the homes of industrialized nations.
When crops are kept in modern refrigerators, they can perish and lose flavor. However, if they
can be stored in a product that offers an environment that has a lower temperature than room
temperature, yet not as cold as a refrigerator -- the produce can last longer, and maintain its
integrity (Augustin, 2011). There have been several projects that tried to encompass these
requirements.
The Terracooler
The Terracooler is a natural cooling system made of terracotta and is bell-shaped, like a
cloche. It is a cover that is double sided with a space between the two walls. As it is made of
clay, the temperature inside the terracooler is 25-40% cooler than the outside temperature, which
preserves food ten times longer than if it were stored without refrigeration (Augustin, 2011).
The design inspiration is derived from the design of metal cloches (See figure 1). A
cloche is a cover for food made of silver that is designed to be bell shaped. The bell shape design
helps keep the food warm. It works by the theory of evaporative heat loss. While there is a knob
on metal cloches, its sole purpose it to make it easier to carry the cover. However, in the
terracooler, the knob is used as a funnel to fill up the space in between the double-sided wall
with water (See figure 2). Touching or feeling the water can measure the water level. The
terracooler has a sufficient amount of water for cooling once the water can be felt by inserting a
finger into the knob. The temperature inside the pot can be measured by touching the outside of
the terracooler. Another design strategy of the terracooler is that it can be manufactured in any
shape or size. It can also be mass produced, or simply produced by a simple potter’s wheel,
which are available all around the world (Augustin, 2011).
Figure 1: Metal Cloche (Augustin, 2011) Figure 2: Multi-­‐purpose knob on the terracooler (Augustin, 2011) Figure 3: The w ater that enters the terracooler as shown in figure 3 goes in between the double walls (Augustin, 2011) Advantages of the Terracooler
The terracooler has many advantages. It protects food against sunlight, insects, and dirt.
This is essential in countries in need of easy refrigeration and storage. Additionally, it can be
readily produced because it made of organic materials and can be stored by stacking on the top
of other Terracoolers, optimizing the use of space. The terracooler can be resized for different
purposes. Access to the food is made easier because of the cover-like design. Also, new jobs can
be created due to the mass production of the terracooler. It can also lower energy bills, and
energy usage for different communities (Augustin, May 15, 2011). Therefore, it can benefit
various communities in many different ways. However, most important of all, it offers a source
of refrigeration to areas that do not have electricity.
Disadvantages of the Terracooler
The terracooler has numerous advantages, but it also has disadvantages. The
disadvantages are due to high humidity and unfiltered water. The terracooler does not function as
well when an environment is humid and there is no ventilation. The cooling effect is reduced
when the air is too humid even if there is hot air present. Also, if the terracooler is left in the sun
for a long time, it will not function effectively because the sun will warm the pot at a higher rate
than the terracooler can cool. The other disadvantage is the terracooler does not function well
when either chalky or salty water is used, as the chalk/salt clogs the pores present in clay
(Augustin, 2011).
Zeer Pots
The technology that is used in the terracooler has been present for years. It works when
water enters the terracotta/clay walls, and then the water evaporates through the outer walls. This
same technology was used in Zeer Pots. These pots are also known as Pot-in-Pot refrigerators. A
teacher from Nigeria invented the pots in 2001. His name was Mohammed Bah Abbas. He
created Pot-in-Pot refrigerators by putting a small terracotta pot into a bigger one. In between the
two pots there is a space. He occupied this space by pouring sand and water into it. The inner pot
gets colder through this process, and it can extend the shelf life of produce ten times longer than
if it were stored at room temperature (Augustin, 2011).
The Zeer Pot can store up to 12kg of food; it can preserve vegetables for up to 20
days; and it can be produced at a low cost of $2. It works because of evaporation and
condensation. When the water evaporates on the outside of the Zeer Pot, there is energy that is
used for the phase change of the water because it goes from liquid to a gas. This energy is called
latent heat evaporation. While the gas that is created from evaporation roams the wet surface,
condensation and evaporation are constantly working to keep neutral conditions. In order to
maintain the evaporation, the energy of the liquid water is decreased, which causes a temperature
drop. This process is known as evaporative cooling (See figure 3). It works best in dry areas that
lack humidity. The Zeer Pot uses this process to cool down the internal temperature of the pot.
The water in the sand evaporates to the top of the pot and outside the outer pot (Rinker, 2014).
Figure 3: Energy Flow in the Terracooler (Rinker, 2014)
Favorable Environment for the Zeer Pot
The benefit of the Zeer Pot is heavily dependent on the environment. Because the Zeer
Pot relies heavily on evaporation, it needs to be used in an environment where there is low
humidity and a fair amount of airflow. The rate of evaporation is highest in places where there is
low humidity (ex: Sudan and North Central Mexico). Therefore, the Zeer Pot would thrive in
these locations. While humidity has relevant influence on the performance of the Zeer Pot,
airflow can also affect its success as it is necessary in order for the Zeer Pot to continue to
function. After the water is evaporated into the outer area of the Zeer Pot, the relative humidity
increases, which decreases the evaporation rate. In order for the cooling effect to continue, the
humidity level needs to decrease once again. Airflow is able to achieve this by replacing the
humid, wet air with dry air. In North and Central Africa, the average wind speed is 2.5m/s or
5.6mph. This wind speed is just the right amount for the Zeer pot to function (Rinker, 2014).
Area Available for Evaporation In the Zeer Pot
The area available for evaporation can have a great effect on the performance of the Zeer
Pot. It can be determined from the surface area of the spherical portion of the outer pot, the
cylindrical portion of the outer pot, and the surface area of the exposed sand in between the two
pots. Different radii of the outer pot were experimented with to see which size was the most
optimal. As a result, the pots with the biggest outer pot radius and biggest surface area performed
best. Three different radii were tested (0.25m, 0.35m, and 0.45m) under the cooling rate of 2.5
m/s, and the pot that had the largest radius had the best cooling effect (See figure 4). However,
even though increasing the surface area solves the problem of the cooling rate, it does add on to
the cost of the pot because more clay needs to be used, and it requires more sand and water to be
used. These factors should be considered when choosing to make a bigger pot. However, making
a bigger pot might be very beneficial for families who are willing to share a pot. Therefore, it is a
decision that the user will have to make (Rinker, 2014).
Figure 4: As the radius of the pot increased, the cooling effect increased (Rinker, 2014).
Disadvantages of the Zeer Pot
While the Zeer Pot can be very useful, it also has some disadvantages. These pots are
extremely bulky so they are not easily portable. Additionally, since they are larger, it is very hard
to access food that is on the bottom of the pot. The pot could also allow insects and dirt to access
the food because it does not have a strong sealing system (Augustin, 2011). Like the terracooler,
the Zeer pot also has some factors that could be enhanced.
Natural Clay Air Conditioner
Clay has been used as a natural cooling device for centuries. Clay has been used in
interesting refrigeration models; Thibault Faverie constructed a natural air conditioner made out
of clay. This air conditioner works with the use of evaporation and clay’s cooling properties. It is
able to cool down the temperature in an environment in a simple and economical manner.
Faverie constructed the Cold Pot (natural air conditioner) while he was studying at the University
of Art and Design Lausanne. He explained briefly how the Cold pot works during his stay. He
explained that the terracotta pot uses evaporation to cool down the surrounding temperature. The
terracotta exterior absorbs the inner liquid and it sends it back to the exterior surface. When the
water comes in contact with air, it is transformed into a gas. When this process occurs, the
aluminum pipe inside the air conditioner cools down (this is where the air circulates). The
aluminum pipe also contains “cooling slices”. These cooling slices are kept cold because an
electrical blower ventilates them. Hot air comes through the pot and it gets cooled as it goes
through the inner aluminum pipe (See figure 4). The Cold pot is also very convenient because it
only uses 2 liters of water. Using only this small amount of water, it is able to cool down the
outer temperature by 8 -10°C, approximately 14.5 -18 °F. Even though this device is not able to
cool down large spaces, it provides inspiration for future simple refrigeration designs (Mok,
2014).
Figure 4: Area of air circulation (inner aluminum
pipe)(Mok, 2014)
Clay
Clay is the name for pounded particles that are organic and sculptable when wet. While
clay is the common name for these particles, scientifically they are hydrous aluminum silicates.
They contain several chemical impurities (potassium, sodium, calcium, magnesium, or iron).
Clay has many characteristics after it is fired or naturally dried. These characteristics include:
elasticity, durability, and contraction. As to the size of clay particles, they are not bigger than
0.004mm. When clay particles come in contact with water, they cluster together and then
disperse and settle in the water. The particles also form colloidal suspensions once in the water
(Earth Sciences: London's Geology, n.d.).
Uses of Clay
Clay has been used since the prehistoric ages. It was used for many different
purposes, such as cooking tools, bricks, and waste pipes. In construction, it was also used for
walls, tills, and floors. Different types of clays were used for various purposes. Fireclay was
often used in the construction world for tiles and bricks because of its resistance to heat. There is
another type called expanded clay, which was also used in construction. Unlike fireclay,
expanded clay is lightweight and was used for insulation. Another type of clay is Bentonite clay,
which was used for purification. It is used to filter and purify different things such as water,
wine, and sewage systems(Earth Sciences: London's Geology, n.d.).
Clay Coated Straw
Clay coated straw is an economical, and abundant resource. The clay coat binds the straw
together, preserving it. For 700 years, clay coated straw has been known to be a source of
insulation that does not decay. For the material, any type of straw would work. Some examples
are: barley, wheat, and other grain straws. Hay should not be used because it is too flimsy and it
contains seeds. Clay can easily be derived, found in places such as river bottoms and riverbanks.
Manufacturers of brick and tiles usually have an ample amount of clay. They would be able to
sell it for $16 per ton, making it an inexpensive resource to use. If necessary, clay can be
harnessed from soil (Sarvasri, n.d.).
Methodology of Clay Coated Straw
It is not a difficult process to obtain clay-coated straw. The first step is to break the clay
apart or crush it into really small pieces. The clay particles have to be small enough so that they
can mix easily with the water. The water and clay should be mixed until the consistency of the
solution is creamy. The next step would be to spread out the straw on the ground, and moisten it
with water. After the straw is wet, the water-clay mixture should be dripped onto the straw. The
layer of clay on top of the straw should not be too thick. This mixture should be 5-10% clay and
90-95% straw. Once the straw is dried up, the clay should not be easily seen (Sarvasri, n.d.).
What is Terracotta?
Terracotta is a type of clay that is fired. It is hollow, lacks shine, and it can be molded
into different shapes, and typically takes a reddish tone. Terracotta’s durability depends on the
temperature it was fired in. However, it is usually very durable and also fireproof. Another
benefit of terracotta is that it is available in virtually any color or design (Terra Cotta:
Characteristics, Uses And Problems, 2012).
Types of Terracotta
There are 4 main types of Terracotta: Brownstone terracotta, Fireproof construction
terracotta, Ceramic Veneer Terra Cotta, and Glazed architectural terracotta. Brownstone
terracotta often takes on a dark red or brownish color. It is often used to replace brick or real
brownstone. It was typically used in the 19th century. Fireproof construction terracotta, while not
being prevalent today, it has the benefits of being lightweight, inexpensive, and non-flammable.
It is most commonly used in the construction of metal beams, floors, and ceilings. Unlike the
Brownstone terracotta and the fireproof construction terracotta, the Ceramic Veneer Terra Cotta,
which is not hollow, is very commonly used today to secure metal into buildings. Glazed
architectural terra cotta is used as an alternative to stone because it is both cheaper and easier to
work with. It is also very strong and resistant. Its characteristics are that of being strong and
resistant, yet hollow and easily molded (Terra Cotta: Characteristics, Uses And Problems, 2012).
Common Problems Associated with Terracotta
There are two main causes of the deterioration associated with terracotta. The first cause
is the natural composition of the terracotta, while the second cause is human involvement.
However, natural deterioration problems generally occur over long time spans, and at a steady
and predictable speed. They can also be prevented through various preventative methods and
materials. Human caused problems, such as vandalism, cannot be predicted and require
emergency attention (Terra Cotta: Characteristics, Uses And Problems, 2012).
Natural Problems Associated with Terracotta
While there are many natural problems that come with terracotta, there are three main
problems. The first is crazing. This is when the outer glaze cracks. This is typically not a major
problem unless the crack gets through the glaze and into the main clay layer. The second
problem is spalling, when layers of clay break or peel off, caused by change of pressure
underneath the clay surface. Change of pressure can occur from the moisture that is trapped
underneath the clay surface when there is an extreme temperature change in a short amount of
time. The last problem is fracturing, which occurs when terracotta is exposed to moisture,
causing the iron in the terracotta to expand, and break (Terra Cotta: Characteristics, Uses And
Problems, 2012).
Bentonite Clay
Bentonite clay is a type of clay that is used to purify the body. It can be consumed in two
different ways, by drinking it with water or putting it on externally. Another common name for
it is Montmorillonite. Many people use it to detoxicate their body and improve their immune
system (Axe, 2015).
History of Bentonite
Bentonite is made from volcano ash; therefore it is abundant where there are many volcanoes,
such as Wyoming. The reason it is commonly known as Montmorillon is because it was first
discovered in an area of France with that name. Throughout history, Bentonite clay has been
used to protect people from illnesses. The people in the Andes, Central Africa, and Australia
used it in different ways. This type of clay can be used in its natural form, without any
processing (Axe, 2015). Therefore, many different cultures can get access to the chemical
without having access to machinery.
How Does Bentonite Work?
People come in contact with various toxins from everyday activities. Toxins can be stored in
various commodities such as paint fumes, extermination fumes, unpurified water, and processed
food. There are also heavy metal toxins such as mercury, benzene, and lead, which can be found
in fish and food products that are high in fructose corn syrup (Axe, 2015).
Bentonite is great for the body because it gets rid of these toxins that we come in contact
with everyday, therefore providing a better immune system. Bentonite does not only rid the body
of toxins, it also has a myriad of vitamins. Many people consume it and treat it as a dietary
supplement. When Bentonite clay comes in contact with water, it takes on a negative charge.
However, most toxins and impurities take a positive charge. This is due to the fact that
negatively charged particles search for positively charged particles to bind with to make them
complete. When the heavy metal/ toxins particles bind with the Bentonite particles, the toxin
removing process begins (Axe, 2015).
Uses and Benefits of Bentonite
Bentonite has a number of different uses and benefits. It can be used to treat eczema,
psoriasis, and copious skin infections. Bentonite clay has the ability to enter the skin pores, bind
with the toxins, and obtain the bacteria. Therefore, many use Bentonite as an antibiotic because it
is able to heal infections and speed up healing time while most antibiotics cannot. It is also very
common to see the use of Bentonite in baths. Many people soak in the Bentonite water as it
removes toxins and hydrates the skin. Another way Bentonite aids the body is that it is able to
absorb oxygen. It is able to take out the unnecessary hydrogen from the cell, allowing more
space for oxygen. As a result, the body can have a better immune system and feel more
energized. Bentonite also has the ability to alkalize the body. Often times, an unhealthy diet can
lead to an acidic reaction in the body. Bentonite, however, can be a great method to balance the
pH in the body because it has alkali minerals, as it is a base. Therefore, it is able to alkalize the
blood, saliva, and urine in the body. Not only does Bentonite alkalize the body, it is also able to
increase the amount of good bacteria, probiotics, in the body. It is able to decrease the bad
bacteria levels existent in the stomach lining resulting in a healthier stomach. Bentonite can also
bind to aflatoxins that are commonly found in nuts and grain products. If these aflatoxins are not
bound with anything, they can result in liver damage and cancer. However, when the negatively
charged particles of the Bentonite bind with these aflatoxins, the stomach is able to withstand the
acidity existent in the stomach. A study that was performed in 1998 also showed that Bentonite
has the ability to help with digestive problems because it is capable of digesting harmful toxins
known as the rotavirus and the coronavirus. These deleterious toxins have the ability to cause
gastrointestinal distress, such as nausea and diarrhea (Axe, 2015).
Bentonite and Magnesium Water Purity
While Bentonite can have many benefits on the body, it also has the capability to purify water. It
was found to be able to eliminate the fluoride that can be found in potable water. However, its
performance can be improved when it is mixed with magnesium. Bentonite can be chemically
altered through the use of magnesium chloride to remove more fluoride from water. The altered
Bentonite, known as MB, was tested under different circumstances. Results demonstrated that
MB can work efficiently in an array of pHs and that it has the capacity to remove 2.26 mg/g with
a starting concentration of fluoride being 5 mg/L. Thermodynamic studies demonstrate that this
process is endothermic. Magnesium Bentonite has also shown been proven to work better in
artificial water rather than natural water (Mater, 2010).
Aluminum Sulfate Chemical Properties
Aluminum sulfate is a chemical compound that is a white powder, that is fragrance free.
It is formed by adding aluminum hydroxide to sulfuric acid. Aluminum Sulfate is also known to
be hygroscopic, meaning it has the ability to hold and soak up water from the neighboring
environment while being water-soluble, making it not flammable. The amalgamation has a
relatively high pH, hence it can burn human skin and abrade metals.
What is Aluminum Sulfate Used For?
Aluminum Sulfate has an extensive array of uses. Its paramount use is to filter water by
causing the adulterations in the water to form bigger particles so that they are easier to sift out.
Aluminum Sulfate is also used in making colorants, antiperspirants, and baking powder, killing
insects, and healing pain. Farmers also use the chemical to raise the acidity of dirt (What is
Aluminum Sulfate?,n.d.) .
Dangers of Using Aluminum Sulfate
Aluminum Sulfate is dangerous if it comes in contact with skin, ingested, or inhaled.
Inhalation of the substance can cause a violent cough and wheezing. If it comes in contact with
skin, it can cause irritation, itchiness, and redness. Ingesting the chemical can cause severe
irritation to the internal organs, resulting in symptoms of vomiting, nausea, and diarrhea (What is
Aluminum Sulfate?,n.d.).
Aluminum Sulfate in Developing Countries
Aluminum sulfate is used as a flocculent, meaning it has the ability to clump together
impure particles and remove bacteria in many different countries. It is abundant in impoverished
countries; it is sold in big, white blocks for little money. Aluminum Sulfate is often referred to as
alum by the native people. It is vastly used by developing countries for filtration because the
preparation process is very simple. The compound is crushed into a powder, stirred in water, and
eventually settles down in the bottom(Pure Gazette Water Treatment Issues, n.d.).
Magnesium Chloride
Magnesium chloride has the ability to cure many diseases as well as reviving the body. Even
though it is surprising to many, magnesium chloride can be used to treat infections. The first to
discover the antiseptic use of the substance was the French surgeon, Professor Pierre Delbet. He
used it on wounded soldiers in 1915. He replaced the old methods with this chemical because the
old methods were proven to cause infections rather than cure them, and kill tissues in the
process. The professor performed many experiments to test the validity of the chemical, and his
tests showed that magnesium chloride cause the white blood cells in the body to kill three times
the amount of bacteria than before. Through his experimentation, Delbet found out that
magnesium chloride can treat colitis and gall bladder problems, Parkinson's disease, tremors and
muscle cramps acne, eczema, psoriasis, warts and itching skin, impotence, prostatic hypertrophy,
cerebral and circulatory problems, asthma, hay fever, urticaria and anaphylactic reactions (Last,
n.d).
Magnesium Chloride Purification
Magnesium chloride is beneficial for detoxification and purification. It can abstract toxins from
body tissues through pores. It can also serve as a digestive enzyme that breaks down proteins and
lipids. It is an essential chemical to have in the body. When it is missing, the body cannot
regulate internal fluids, move muscles, or have regular kidney function. Also, elderly who suffer
from chronic diseases often times have a magnesium deficiency, causing them to lack in
hydrochloric acid. Therefore they cannot intake oxide or carbonate which are essential for the
body (Dr. Sircus, 2012).
Lit Cited:
1. Augustin, S. (2011, May 15). Terracooler, natural food cooling with terracotta and
water. Retrieved September 28, 2015, from http://terracooler.org
2. Axe, J. (2014, October 22). 10 Proven Bentonite Clay Benefits & Uses. Retrieved
December 18,2015, from http://draxe.com/10-bentonite-clay-benefits-uses/
3. Sarvasri, S. (n.d.). Natural Insulation -- Regulating Heat and Cold. Retrieved
September 28, 2015, from http://www.planetaryrenewal.org/index.html
4. Rinker, P. (2014, August 1). Zeer pot refrigeration (design). Retrieved September
29, 2015, from http://www.appropedia.org/Zeer_pot_refrigeration_(design)
Mater, H. (2010, August 15). Result Filters. Retrieved December 18, 2015, from
http://www.ncbi.nlm.nih.gov/pubmed/20462694
5. Mok, K. (2014, April 4). Natural air conditioner cools with the power of terracotta
and
evaporation.
Retrieved
September
29,2015,from
http://www.treehugger.com/sustainable-product-design/natural-air-conditionerterracotta-thibault-faverie.html
Terra Cotta: Characteristics, Uses And Problems. (2012, November 13).
Retrieved September 30, 2015, from http://www.gsa.gov/portal/content/
6. Earth Sciences: London's Geology. (n.d.). Retrieved September 30, 2015, from
http://www.ucl.ac.uk/earth-sciences/impact/geology/london/ucl/materials/clay
7. What is Aluminum Sulfate? (n.d.). Retrieved December 18, 2015, from
http://www.aluminumsulfate.net
8. Pure Water Gazette Water Treatment Issues. (n.d.). Retrieved December 18, 2015, from
http://www.purewateroccasional.net/wtialum.html
9. Lost, W. (n.d.). Magnesiumchloride. Retrieved December 18, 2015, from
http://www.healthscience-spirit.com/magnesiumchloride.html
11. Dr Sircus. (2012, December 27). Magnesium Chloride Benefits. Retrieved December 18,
2015,
from
http://drsircus.com/medicine/magnesium/magnesium-chloride-
benefits
12. Gronewold, N. (2009, November 24). One-Quarter of World's Population Lacks
Electricity. Retrieved December 11, 2015, from
http://www.scientificamerican.com/article/electricity-gap-developing-countries/
Name: Malak El Khalkhali
Date:11/13/15
Massachusetts Academy of
Mathematics and Science
Engineering Plan
A. Engineering problem being addressed:
In impoverished countries, having access to refrigeration can be challenging if not impossible.
Therefore, there is a need for a simple, and inexpensive refrigeration system that can be built
using only organic and indigenous materials.
B. Engineering Goal:
The engineering goal of this project is to develop a clay refrigerator that can be built from
organic and inexpensive materials.
C. Description in detail of methods or procedures:
Design Criteria:
This experiment will try to improve an existing natural clay refrigerator called the
terracooler. It will enhance the terracooler by making it work better in humid environments and
naturally filter the dirty water that is used in the terracooler so that the clay pores do not get
clogged. These project will fix these problems by using clay coated straw because it allows more
air to pass through the gaps in humid environments than regular clay, and will test whether
bentonite, bentonite magnesium, or aluminum sulfate is the best water purifier.
Testing:
The device will be tested in different ways in order to test for both humidity, and water
purity. Water purity will be tested first because the problem of water impurities clogging the clay
is a bigger problem. The amount of bacteria/impurities existent in the water will be tested using
Agar plates to culture the bacteria. Using those results, the best chemical for purifying water will
be determined. Then, the prototype will be built using clay coated straw. Another prototype
using normal terracotta will be built for comparison purposes. The prototypes will be placed in a
humid environment, and the internal temperature will be compared between the two different
prototypes.
Bibliography:
1. Augustin, S. (2011, May 15). Terracooler, natural food cooling with terracotta and
water. Retrieved September 28, 2015, from http://terracooler.org
2. Axe, J. (2014, October 22). 10 Proven Bentonite Clay Benefits & Uses.
Retrieved November 13, 2015, from http://draxe.com/10-bentonite
clay-benefits-uses/
3. Sarvasri, S. (n.d.). Natural Insulation -- Regulating Heat and Cold. Retrieved
September 28, 2015, from http://www.planetaryrenewal.org/index.html
4. Rinker, P. (2014, August 1). Zeer pot refrigeration (design). Retrieved September
29, 2015, from http://www.appropedia.org/Zeer_pot_refrigeration_(design)
5. What Is Aluminum Sulfate? (2008). Retrieved November 13, 2015, from
http://www.aluminumsulfate.net