DRY ICE

Evening Star, Issue 21835, 26 September 1934, Page 14

DRY ICE

NEW COOLING MEDIUM SOLID CARBON DIOXIDE EXTENSIVE USES. In the space of a lifetime the mechanical refrigerator has developed from its infancy to a stage of perfection. in which it is a vital factor for the existence of the human race. Such a statement, which appears at first to he extravagant, is justified when it is realised that more than three million tons ot food arc imported annually into this country in refrigerated ships; an amount which averages about seven ounces each day for every man, woman, and child in Great Britain. Some idea of what this means is obtained when it is known that the average weight of food consumed each day by one person is about two and a-half pounds (says a writer in a recent number of ‘ Discovery ’). The first cargo of meat to be brought successfully from Australia arrived in Loudon in 1880 and this was followed in 1882 by the first shipment from New Zealand, a country which to-day sends more than 80 per cent, of its exports in refrigerated ships. The importance of refrigeration to _ the Mother Country and to the dominions is therefore sufficiently apparent to make further emphasis superllous. Moreover, the necessity for largo ciM stores and for domestic refrigerators is by now appreciated; but what is not quite so well known is the immense and rapidly increasing importance of this comparatively new branch of engineering in many manufacturing processes. For example, in addition to the more obvious uses tor ice and icecream manufacture, it enters into the manufacture of such diverse things as chocolates, margarine, biscuits, beer, optical lenses, golf balls, cinematograph films, and artificial-silk stockings. These applications have been chosen at random from a list of about three hundred. Two hot summers in succession have drawn more than the usual amount of attention to the advantages, in fact, the necessity of refrigeration, and it is appropriate that there should bo at the Science Museum in South Kensington an exhibition designed to illustrate the applications of refrigerating machines and the ways in which they achieve their purpose. Visitors to the museum will see how refrigerators arc able to keep the air in an enclosed space at a controlled low temperature. They will also see in addition to the jycil-knowQ aiffilicatiofts of

food storage and transport, models which have been specially constructed for the exhibition to illustrate a few of the ways in which refrigeration enters into industrial processes. One of the most recent applications of scientific discovery is the use of solid carbon dioxide on a commercial scale as a cooling medium. For many purposes it has replaced water ice and its particular use, known to everyone, is that of preserving ice cream at a low temperature in the thousands of tricycles now so familiar in all parts of the country. It is cpiestinnable, however, how many realise that the substance, sometimes Jaioivn as _ “ dry ice,” which is used in these tricycles, is of almost as simple a nature chemically as water ice. The men who handle it daily very often regard it as a mysterious chemical and all they know of it is that it is very cold and that it should not be handled without gloves. CARBON DIOXIDE’S NATURE. Every substance exists in three forms, or states, the solid, liquid, and gaseous states. Water provides probably the best example, as in two of its states, liquid and. solid, it is provided by Nature, while in its gaseous state s , steam, it is also familiar. Carbon dioxide suffers from the disadvantage that it has never been given a simple name but is always known by its chemical title. At ordinary atmospheric temperatures it exists only as a gas, and probably it is best known as the gas exhaled in the process of breathing or as the gas which is given off by plants and trees. As a solid and liquid it has been known to scientists for almost 101) years—the discovery of the solid is attributed to Tbilorier in 1805—and the strange thing is that although the manufacture has 'formed one of the simpler experiments done in the earlier years of a school or college <-our.se in science, it was not commercialised until 1924, only ten years ago. The first factory was constructed in Montreal, In the next year dry icc was made on a large scale in America and its production very soon followed in England. A system of distribution had to bo builtup and there were certain technical difficulties to bo overcome. All this took a certain amount of time and it is only comparatively recently that it lias been possible to obtain it easily in most districts. Very shortly it should be more readily available than water ice. SO COLD THAT IT BURNS. Naturally the principal properly of importance of this substance is its extremely low temperature. This is minus ]o9deg' Fahrenheit. or I lldog below the temperature of water ice. Paradoxical as, it may sound, dry ice causes burns il handled without gloves; it blisters tho skirt, just as a hot gubstauoQ

will. Duo to this low temperature the first use, and still the largest use, of solid carbon dioxide was the storage and transport of ice cream. It is much more satisfactory than water icc for this purpose, and it has the added advantage that in passing from the solid to the gaseous state it leaves no liquid behind it, and in this it is vastly superior to water ice, which, when melting, is liable to make a moss. EASILY KEPT SOLID. One might imagine that because of its low temperature solid carbon dioxide would evaporate so quickly that it could not be kept for a sufficient length of time to be of any use, but this problem was readily overcome. Firstly, it mlist be stored and transported in heat-insulated containers, ami secondly the containers must allow the gas to escape, otherwise a dangerous pressure would be built up. Jt may thus be kept for several days with only a slight loss in weight. One outcome of its ease of transport and of the fact that it can bo carried in light containers while occupying much less space than the gas, is that it is being found economical to carry it in this form even though at a later stage it may be required in the gaseous state. At the exhibition at the Science Museum, in an exhibit arranged by the Low Temperature Research Station; it is shown that the storage life of meat, fish, and fruit is prolonged by til© introduction of carbon dioxide •ms, a truly remarkable development which will have a marked eft'cct upon tho feeding of the population of the country. It will be seen, therefore, that when dry ice is used as a refrigerant it lias tho additional advantage of increasing the time which the food in the cold chamber will keep in a good condition. Moreover, by penetrating the insulation of the chamber it improves the insulating properties. Among the other commercial applications of carbon dioxide in the gaseous state is tho manufacture of aerated mineral waters and bottled beers; and in its solid state it is used by hospitals for cauterisation, in the form of ‘'•carbon dioxide snow,” tho product ot the simple laboratory experiment mentioned earlier in this article.