Service chemistry : being a short manual of chemistry and metallurgy and their application in the naval and military services / by Vivian Byam Lewes and J.S.S. Brame.

  • Vivian Byam Lewes
Date:
1913
Catalogue details

Licence: In copyright

Credit: Service chemistry : being a short manual of chemistry and metallurgy and their application in the naval and military services / by Vivian Byam Lewes and J.S.S. Brame. Source: Wellcome Collection.

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    dioxide, the ethylene in turn becomes a liquid, which, when it boils at atmospheric pressure, gives a temperature of — 100° C., but if the conversion into the gaseous state is hastened bv allowing it to gasify into a vacuum the temperature is lowered to — 140° C. At — 140° C. oxygen can be liquefied by pressure, and on allowing liquid oxygen to boil at reduced pressure a temperature of — 205° C. is reached, a point at which air liquefies by merely coming in contact with the cooled surface. Cooling hydrogen down to this temperature under a pressure of 180 atmospheres and allowing the gas to escape from a fine nozzle into a vacuum vessel also cooled to the same temperature. Sir James Dewar liquefied hydrogen in considerable quantities. The reduction of temperature consequent upon the expansion of a gas when released from a high pressure, can be utilised to further cool another quantity of compressed gas, which on being released from pressure in turn gives a still greater degree of cold, and this may be continued until a lowering of temperature suffi- ciently great to liquefy air can be obtained. This principle is utilised in the forms of apparatus devised by Linde and Hampson respectively, and which are now emploj-ed for making liquid air on a commercial scale. Refrigerating’ Machines.—The principles involved in the beautiful series of researches that have led to the liquefaction of all gases, have also received most useful application in the reduction of temperatm-e necessary for the production of artificial ice and cold storage, both on land and sea. For this purpose it is necessary to maintain indefinitely the temperatui’C at a few degrees below the freezing point rathei’ than to obtain an excessively low temperature, and the processes employed may l>e grou]ied in three' classes :— 1. Those in which air is compressed by powerful compressing pumps with evolution of heat, which is absorbed by ])assing the air through a coil cooled by water. The compiessed air is tlieii allowed to flow into an expansion cylinder, and in expanding takes up and renders latent as much heat as it gave out on compression, and thus cooled several degrees below the freezing point it enters the refrigerating chamber, from which an equivalent volume of air is then ^vithdrawn to the compressing pump. 1,'he drawbacks to this system are its low efficiency, which makes the space occupied by the plant large as compared with refrigerating
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