IPad Apps

rocks and minerals app
Rocks and Minerals
structure of earth app
Structure of earth
simple machines app
Simple Machines
magnets app
adaptations in animals app
Animal Adaptations
adaptations in plants app
Plant Adaptations
diseases app
solar system app
Solar System

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IPad and IPhone Apps

Educational Games for IPad and IPhone. English Grammar and Science Apps for Elementary and Middle School Kids.


Refrigerators or fridges are a relatively new development. However, the concept of cooling food to preserve it is an age-old tradition.

Perhaps the earliest known time that man was known to have cooled foods is in China around 1,000 B.C.

The Chinese used to make use of all the cool streams, springs, caves and cellars to store their food.

The world’s oldest cellars were holes dug in the ground, which were lined with straw or wood and then packed with snow or ice. Food kept in them used to last longer.

Later, during the Egyptian Empire in 500 B.C. Egyptians used to keep their clay pots filled with water out in the cold night, so that by morning the water would be ice.

Between the 14th and 17th centuries, man figured out that salt water was capable of absorbing heat and therefore, anything kept in salt water would stay cold.

In the 18th century, “ice houses” became quite common. They were large shed that kept sheets of ice packed in salt, and wrapped in strips of flannel, stored underground until summer.

During this time, specifically in 1748, Dr William Cullen became the first person to show how artificial refrigeration actually worked.

Unfortunately, Dr Cullen’s work never really took off and for quite a while afterwards many different people experimented with different types of artificial refrigeration.

Even though many people influenced the invention of the refrigerator, a physician called John Gorrie constructed a working model of it in 1844 that is still used today.

The licence for the invention of the principle of freezing belongs to a German engineer Carl von Linde in 1877.

He invented a continuous way of liquefying gasses on a large scale. Refrigerators work on this mechanism today.

By the 19th century “Ice boxes’ had become quite popular and these would become the great grand fathers of our modern day refrigerators.

These ice boxes were wooden boxes lined with tin or zinc and had cork, sawdust, and seaweed to hold the blocks of ice in place. A drip pan collected the water that melted and had to empty every day.

The ice had to constantly replaced, and it was done by purchasing blocks of ice from the “ice man” who used to ride his wagon in the streets.

Later improvements on the icebox used toxic gasses, which caused many accidents and were then not used anymore.

In 1911, General Electric released perhaps one of the earliest working models of the fridge, which operated on Freon, a safer gas than those used earlier.

Two years later the first fridge for home use was introduced, and from then on, the refrigerator saw massive improvements and modifications.

Today the refrigerator is a common household appliance which as a heat insulated section and a heat pump (often electrical) which sends heat from the inside of the fridge outside, so that the inside is cooled to a temperature below room temperature.

In America, almost 99.5% of Americans have fridges in their homes, and these appliances have become common furniture in restaurants, hotels, subway stations, and businesses.

Modern fridges have two sections; the bigger fridge compartment with a temperature above the freezing point of water, and the freezer with a temperature below the freezing point of water.

There are also many new features that have been introduced like the automatic defrosting (so that the ice formation does not get too much), chilled water dispensers, adjustable shelves and trays, temperature display, controls, indoor ice maker, and many more.

Modern refrigerators are made to be energy efficient; that is they do not use as much energy as earlier, but the energy that they do use is utilized to the maximum.

With the increase in environmental awareness, refrigerators are built so that no harmful gasses (greenhouse gasses) are released.

Solar water heating systems are made from old refrigerators. Some others have been modified for low-income families and exchange programmes of ‘change your old refrigerator for a new one’ have been started.

These old refrigerators are recycled so that their different parts like the gas, copper, class and iron can be used for other things, without polluting the environment.