The Statutes providing for patents in the United States require that the inventor "shall file in the Patent Office a written description * in such full, clear, concise, and exact terms as to enable any person skilled in the are or science to which it appertains, or with which it is most nearly connected, to make, construct, compound, and use the same; and in case of a machine, he shall explain the principle thereof." Therefore, a patent application should describe the invention in such terms and in accordance with the principle or theory recognized and understood by the greater number of persons skilled in the refrigeration art. In this dissertation an outline is made of the theory of mechanical refrigeration as understood and accepted by the refrigerating profession today, and it is hoped that from it both the inventor and the patent attorney may be aided in the development of the invention and in the preparation of the patent application, by gaining a better understanding of the viewpoint of the Patent Office which, after all, is only a reflection of the viewpoint of the art as shown by its printed records.

As a general proposition, in the exact science of physics and its practical development, engineering, it is seen that energy in its various forms is impelled, through its own nature, to flow from states or conditions of high potential to states or conditions of a lower potential, performing work during its flow, and in order to force the flow of energy in its various forms in the opposite direction an expenditure of work is always required. In this connection, it is noted that the term "potential" itself is merely based on theory. It has been observed that energy always naturally progresses in the same direction and from a first relative condition or position to a second. The term "high potential" has been selected to designate the first relative condition or position and "low potential" to designate the second.

Thus, water flows down hill, namely from a position at a given distance from the center of the earth (high potential) to a position nearer the center of the earth (low potential); electricity flows from a charged body of high

potential to a body of lower potential and heat flows from a body of high potential or high temperature to a body of a lower potential or a lower temperature.

In order to reverse this natural action, it is necessary to perform work. Thus, in order to force the water to flow uphill it is necessary to use a pump; in order to force electricity from a low to a high potential it is necessary to employ a dynamo or generator, which may be termed a pump for pumping electrical energy; consequently, by analogy, it is said that apparatus which is used to force heat from a lower temperature to a higher temperature (or in other words mechanical refrigeration apparatus) is a "heat pump" and the act of transferring heat from a body of low temperature to a body of high temperature against the natural tendency of flow of the heat is termed "heat pumping."

Refrigeration apparatus may be divided into two classes, which may be termed "natural" and "mechanical" refrigeration apparatus. In "natural" refrigera tion apparatus, heat flows in its natural direction, that is, from a comparatively warm body (higher temperature) to a cooler body (lower temperature). This dissertation is not concerned with this type of apparatus. Other refrigeration apparatus, which, through its arrangement and operation causes the flow of heat in the unnatural direction, or from a cold body (low temperature) to a relatively warm body (high temperature) is usually termed "mechanical refrigeration apparatus' and is named "heat pumping apparatus."

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A mechanical refrigeration apparatus as a heat pump takes in heat at a comparatively low temperature in the refrigerator member of the body to be cooled and ejects the heat at a higher temperature through a medium, such, for example, as the condenser cooling water. It is apparent that a mechanical device utilizing a medium for carrying away the heat, the temperature of which is lower than that of the refrigerator, is impractical as a heat pump or refrigeration apparatus, because obviously it would be better to use that medium, which may be cold

cooling water, to directly cool the refrigerator than to go through the then unnecessary steps of a refrigerating process. This would be analogous to forcing water To flow down hill by means of a pump, when as is obvious, it would be better and cheaper to allow the water to flow down hill through the natural force of gravity. Consequently, the art of mechanical refrigeration is usually confined to pumping of heat from temperatures below those of the commoner cooling agents, such as atmospheric air, river or sea water or the water supplied to cities from the reservoirs to those temperatures.

The inventor, the patent attorney and the Patent Office have a common object in view, that is, to determine the scope of an invention, and all are interested in all of the phases of the invention. In the art of mechanical refrigeration the first question that arises in the investigation of an invention, no matter by whom the investigation is made, is whether the invention lies in the field of mechanical refrigeration or is of broader or more limited scope. Two simple tests may be applied to every process and apparatus purporting to involve refrigeration by answering two questions: (1) Does heat flow through the apparatus or system substantially continuously and (2) does the heat flow into the apparatus or system at a lower temperature than that at which the heat flows out of it? If both of these questions can be answered in the affirmative, the idea is one of mechanical refrigeration, but if either one of them is answered in the negative, either the idea does not involve mechanical refrigeration or it is directed to an inoperative process or construction.

It is to be emphasized that all cooling or reduction of temperature is not heat pumping. Consider for example, cooling a gas-engine by means of a water jacket or by a circulation of air over the surface of its cylinder. In this case the temperature of the cooling water or the cooling air is below the temperature of the engine and the heat is carried away at a lower temperature than the temperature at which it flows into the apparatus. The heat then is flowing in the natural direction, involving merely

simple heat exchange. Whether the temperature of the body to be cooled is very high, as in the case of the gas engine, or very low, heat pumping is not involved as long as the temperature of the medium carrying the heat away is lower than the temperature of the body to be cooled. Suppose liquid air at a very low temperature is passed through pipes embedded in ice. Heat would naturally flow from a comparatively warm ice to the cold liquid air and the cold liquid air would carry the heat away from the ice, at a temperature lower than the temperature of the ice, and although all temperatures concerned. are very low and convey at once to the lay mind the idea of refrigeration, the proposition is one of heat exchange solely and does not involve heat pumping. Again, suppose the temperature of a body of a very high temperature is to be reduced and the heat carried away from that body by means of another body the temperature of which is higher than that of the first body. Here, although all of the temperatures may be above the boiling point of water and thus are not thought of as in any way connected with refrigeration, yet heat pumping is required. It is not conceivable that such a heat transfer would ever be put to practical use, due to the simplicity of the reduction of temperature by heat exchange; consequently practically all refrigerating or heat pumping is done at temperatures at least below ordinary atmospheric or ordinary water temperatures.

In all apparatus for refrigeration or for pumping heat, it is necessary that not only the temperature be reduced but that there be a continual flow of heat away from the apparatus. The means by which this flow of heat away from the apparatus is consummated is usually termed in the art the "heat outlet," and in determining whether the apparatus is operative or not the first thing to be observed is whether or not there is a heat outlet. The second test to determine whether or not refrigeration or heat pumping is involved is to determine whether the temperature at which the heat flows from the apparatus through the heat outlet is above or below the temperature

of the refrigerator, the latter being the temperature at which heat flows into the apparatus. If there is no heat outlet, the apparatus is inoperative. If the temperature at which heat flows from the apparatus through the heat outlet is below the temperature of the refrigerator member, or the temperature at which heat flows into the apparatus, the device is impractical and, therefore, inoperative as a heat pump for the reason that it is not working against potential, although it may then be operative as a simple heat exchanger.

Refrigeration is produced mainly by one of four methods; these methods being exemplified in four types of refrigeration apparatus, viz., the fusion type, the chemical type, the evaporative type and the gas expansion type.

In the fusion type the latent heat of fusion of a solid material, such as ice, is utilized to cool other material the temperature of which is higher than the temperature of fusion of the solid body. Heat pumping is obviously not involved, because the cooling body is always at a lower temperature than the body to be cooled, the heat flowing in its natural direction.

In the chemical type two or more chemicals react with cach other, the reaction being endothermic. The combined chemicals contain less heat than the separate ingredients, which results in the withdrawal of heat from the surrounding bodies or a lowering of temperature of the combined chemicals. The energy required to produce the cooling lies dormant in the uncombined chemicals and it is noted that it is necessary to continually combine fresh quantities of chemicals in order that the cooling action may be continuous.

Sometimes mechanical power is required to bring the chemicals into that intimate contact necessary to permit the endothermic reaction. The heat of refrigeration passes into the materials which combine, causing what is known as a chemical change in the chemcals, analogous to the change of state of ice as it melts to produce refrigeration or cooling. In order that ice may take heat from a body it is necessary, as has been stated, that the body