Cold Storage and Bacteria Science Project. Investigate refrigerators, and rapid evaporation cooling. Science teachers can also use this as a bacteria and refrigeration lesson plan or exercise.
Science Experiment - Growth of Bacteria in Air
Expose to the air a Petri dish which has been kept until the culture medium has become dry.
The facts which we have learned from these experiments will have many applications both in our home life and commercially.Some of these which most concern us in our everyday life should be considered. Science Fair Projects - Bacterial Growth in Cold Temperatures Use of cold in the home in checking the growth of bacteria. (a) You at once think of the ice chest or refrigerator.Let us see if we can understand how the refrigerator is so effective in preserving our milk, meats, and vegetables.First, why is ice used in a refrigerator?You will at once say, because it is cold; but you know that a block of wood or stone or iron which might be just as cold is never used in place of ice.The reason for this use of ice may be illustrated by the following experiment. Temperature and Bacterial Growth Science Experiment Nearly fill two beaker glasses with water of the same temperature.Note the temperature.Place in one of the glasses a piece of ice and in the other a stone of equal size which has been kept on ice and has the same temperature.Place the two glasses side by side and apply gradually an equal amount of heat.Note the temperature from time to time.Result?What effect does the melting of ice have upon the heat of the surrounding water?Is this not what you would expect?The removal of heat from water causes it to change into ice, so heat must be used up to change the ice back into water.Do you think that!Your re frigerator will be made colder by covering the ice with pads to keep it from melting? Properties of a Refrigerator - Science Project An ice chest or refrigerator is essentially a box whose walls are so constructed that they are poor conductors of heat.This is usually accomplished by having in the wall an air space which is packed with charcoal or some other poor conductor.The ice in a refrigerator should be placed near the top.The melting of the ice cools the air in contact with it.The cold air falls.(Why?)In so doing it forces the warm air to the top where it in turn is cooled and replaces the air which has been warmed by coming in contact with the food.The effectiveness of the refrigerator depends upon the circulation of air within it; and accordingly care should be taken that the free passage of air is not obstructed in any way.
The ice chest is simply a means of checking the development of bacteria but by no means does it stop their growth.In a large ice chest, food may be preserved for a considerable length of time but it finally will decay.In small ones, food may be kept for only a few days.All refrigerators should be frequently cleaned, as dirt and particles of fo6"d furnish a place for the growth of bacteria, and after a time render the refrigerator unfit for use.
Various methods have been used in homes where ice cannot be obtained to provide a low temperature for the protection of food against the action of bacteria.Cool cellars, cold running water, spring houses, andsuspension in deep wells are means frequently employed.An iceless refrigerator may be made as follows :
Cover a frame of wood with cloth such as duck.Sew a number of lamp wicks to the edge of the cloth and allow the other end of the wicks to extend into a vessel of water on top of the frame.The water soaks into the cloth through the wicks.As heat is used up in evaporation of water, the temperature within the refrigerator is lowered to 50-56 degrees F. The efficiency of this refrigerator is, increased if it is kept where there is a current of air.Why ?
In tropical countries, drinking water is kept in porous earthenware jars.Why? Science Project Idea - Cold Storage and its uses Investigage the use of cold in storage warehouses.In cold-storage plants low, constant temperatures are maintained.Definite temperatures are kept in different rooms, as not all foods are best preserved at the same temperature.Fruits are stored at a little above freezing; fresh meat, at about 25 degrees F. ; poultry, at about 15 degrees F. ; fish, at about degrees F.
The question arises, How are these steady low temperatures produced,?As ice is not used, a review of the principle of the iceless refrigerator may help us.(Explain the production of low temperature in the iceless refrigerator.)Cold-storage plants generally use ammonia which has been changed into a liquid from a gas by pressure.When the pressure is released the ammonia returns to its gaseous state, taking heat from everything around it. The effect of rapid evaporation (changing a liquid into a as) may be illustrated by the following experiment. Rapid Evaporation Cooling Science Experiment Place some chloroform or ether in a thin watch crystal.Place the crystal upon a drop of water.Through a tube blow a current of air upon the chloroform or ether.As soon as it all has evaporated, notice the condition of the water.What is the result?What conclusions can you draw? Ammonia which has been made liquid passes slowly through the regulating valve into pipes in which the pressure is very low.The ammonia quickly changes into a gas, absorbing heat in doing so from everything around it.The ammonia gas is removed by the pump at the left of the figure and is changed again by pressure and the spray of cold water into liquid ammonia.
The development of cold storage has been of great advantage both to producers and to consumers.Consider the condition which existed before the use of cold storage in the peach region of Michigan for example.Thousands of bushels of peaches ripened in a few weeks, with the result that the Chicago markets were swamped.Prices went down to almost nothing ; but even then enormous quantities rotted.Sometimes the money received for the peaches was not sufficient to pay the transportation and brokerage the fruit growers received nothing for their year's work.Did the people of Chicago profit by this condition?It is true that for a short time peaches could be bought for a very low price; the peach season was, however, made extremely short.
Since great storage plants have been built, conditions have changed entirely.Now, only enough fruit is put upon the market to supply the normal demands; the surplus is put into cold storage warehouses to be taken out and sold as the supply direct from the orchards decreases.The producer now receives a fair return for his labor and investment.The consumer has a lengthened peach season and there is a minimum of waste.
It is now possible to have fresh at any season of the year the perishable foods produced at almost any other season.
Without cold storage the supply of such foods as butter and eggs and some other foods would be so limited at certain times of the year that they could be used only by the wealthiest people.
By means of cold-storage cars and ships, perishable foods may be transported almost any distance.American fresh meat is sold in the markets of London and Paris.Argentine beef is put on sale in American cities.Fruits of California and the southern states are delivered with little or no loss of flavor to every city in the country.
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