NEW HELIUM GAS

Evening Star, Issue 23093, 20 October 1938, Page 2

NEW HELIUM GAS

SCIENCE DISCOVERY Helium, which was first publicly shown to the Royal Society 43 years ago by Sir William Ramsay, is now all but indispensable for safety in airships. Its lifting power is little less, than that of hydrogen, and, unlike hydrogen, it will not catch fire. Ramsay’s first sample was enclosed in a capillary glass tube no thicker than a fountain pen, and shone a brilliant yellow when electrically excited —a precious gem of purest ray serene. Helium is the inert gas which most strongly resists freezing, or, in other words, the reduction from the gaseous to the liquid or the solid forms. The efforts to subdue it have to take place at a degree of cold closer to absolute zero, the bottomless pit of temperature, then in the presence of any other element. Those who experiment /with it have got within the thousandth of a degree of that unattainable goal, but it must always be beyond reach. It is not their purpose in reducing the gap to attempt the impossible, but to ascertain what changes take place in the properties of bodies in these abysses of cold. They seek to know why. bodies should there conduct heat or electricity bettfer. and how their framework of atoms and molecules is altered by the conditions. , In so seeking they have lately come on the unexpected fact that when helium is frozen to a temperature round about 453 deg Fahrenheit, below that of melting ice_, it "is resolved not into one liquid helium, but into two. When it is situated at rather less than sdeg Fahrenheit above absolute zero, the ordinary liquid helium changes into another form, liquid helium 11., which is completely unlike any other known substance. Cool it still further and it expands instead of contracting. , It becomes extremely sticky; ?t conducts million times better than the helium froin which in a flash jt has just been transformed, and 500. times better than uncooled copper. It conducts electricity so well that it seems to offer no resistance whatever to the stream of electric particles. These disclosures, which have been arrived at by inexhaustible patience and ingenuity at Leyden, where helium was first liquefied, at London, and at Oxford, may be compared with almost as many years ’work by Dr P. W. Bridgman in America, not on low temperatures, blit on high pressures, says E. S, Grey, in the ‘ Observer.’ Some curious resemblances are apparent in a recent summary of some of his results and methods. _He notes that the pressure he attains in his laboratory are the equal of those existing at a depth of 100 miles in the earth’s crust. More than 90 per cent, of the earth’s material is at a lower depth, but it is something to have reproduced in a laboratory pressures existing in 7} per cent, of the globe, and so to be able to guess at what may take place among the foundations or the continents, LIQUIDS AND SOLIDS.

Dr Bridgman’s hydraulic rams can produce pressures of 750,0001bs to the square inch. What effect have these pressures on liquids and solids? Most substances expand when they melt from the .solid into the liquid state. • . ' But there are three—ice when it melts into water, bismuth, and gallium —which contract. Helium’s change or state when further follows the commoner law of expansion. When the commonest class of substances are subjected to high pressures the temperature at which they exhibit a change of state can be raised by hundreds of degrees. Thus at 390.0001bs to the square inch, mercury freezes solid while it is as hot as boding water. Water itself, one of the anomalous liquids, exhibits still stranger transformations under pressure. _ At 33,OOOlbs to the square inch, ice* remains water, though the surrounding temperature is that of an Arctic m'd" winter. A little more pressure and it suddenly collapses and decreases td volume, thus showing that ■ its molecules are now arranged in a new crystalline form. This does not exhaust the changes as pressure increases. The ice alters its form and constitution over and over again, till seven different kinds of iee have been produced. At a pressure of GOO.OOOIhs to the square inch, an iee appears which will melt into water onlv at a temperature of 376 deg Fahrenheit.

Dr Bridgman has applied his pressures to 100 different elements and compounds, and finds that under the compulsion of his hydraulic rams new forms are continually produced. Ice, as noted, has seven different forms, bismuth four, gallium _ three,camphor eleven, and few materials are exempt. All are compressible, solids as well as liquids. The changes they undergo result first from the squeezing closer of their molecules—“ taking out the slack,” as Dr Bridgman phrases it. It is to find what these are that temperatures are pushed lower, and pressures higher. V