Boiling Points.

Bush Advocate, Volume XI, Issue 866, 2 December 1893, Page 6

Boiling Points.

It may seem superfluous to observe that there ate more boiling points than the boiling 1 point of water, yet a considerable number of persons so seldom have any other brought under their notice, that they not infrequently Bpeak as if it were really tho only one, ant', moreover, as if it were quite independent of any external oanditiona and never varied. Were this the case, many soientifio calculations would be considerably simplified ; but, on tho other hand, it is muoh to be doubted whether either soientintß or non-aoieutists would appreciate the very extraordinary world in which they would bo called on to live ; for a oommon boiling point would mean that under the same oxternal conditions all bodied would be in the solid, liquid or gaseous state together. Therefore, we should have either nothing to oat, nothing, to drink or nothing to breathe. In other words, life would be impossible, or would be adapted to conditions very different from those with which experience has made us familiar ; and it is partly by giving to every _ substance its own boiling point, or rather its own set of boiling points, for the fixed temperature even for the same substance is a fallacy, that nature has rendered our physical environment suitable to our needs.

What is generally understood by the boiling point of water is a temperature of 2 12deg. on the Fahrenheit thermometrio scale, bat vulpine climbers know well that on a high mountain water boils at a very much lower temperature than this — on the summit of Mont Blanc at IS-idog. The reason is that at these altitudes the pressure of the atmosphere is greatly reduced, since the density of the air decreases with distanoe from the earth's surface, so that the water is able to expand with greater ease on the application of heat, and consequently passes more readily into the vaporous condition, in which the volume of a given mass of any substance is always far greater than that of the same mass when liquid. The boiling point of a liquid is therefore seen to depend not only on temperature bnt on external pressure, and tho boiling point of water at 212deg. corresponds to what is called "a pressure of ono atmosphere," approximately 151 b. to theßqaro inoh, or a pressure oapable of supporting the column of mercury 'in a morourial barometer at a height of 29'9iu. This is the average pressure of the atmosphere at the sea level, and if it is reduced the boiling pointis lowered, while if it is iuoreased the boiling point is raised. Thus for a pressure of 28'0in., which would be that of the atmosphere at about I,oooft. above the sea level, thn boiling point is lowered nearly 2deg. Fahr., and for a pressure of 31in. it is raised from 212defr. to 213-Bdepr. A very curious result is arrived at if we place a vessel of water in tho receiver of an air-pump, and reduoe the pressure to '006 of an atmosphere, for then the water boils at 32deg., viz., at its freezing point at ordinary atmospheric pressure. Since it is quite possible with modem applicancea to pioduce a vacuum so nearly perfeot that tho pressure is reduced to the millionth of an atmosphere, It will be readily understood that not only can water be made to boil at its usual freezing point, but at a very muoh lower temperature still. Kot only are there substanooß whiob. can be made to boil at very low temperatures, but which require thorn in order to do so at all. liivea among those bodies wliioh at tho ordinary atmospheric pressure maintain the liquid slate, there aro very great differences in the temperature of the boiling poiut. Thus at n pressure of one atmosphere, water boils at 212rieg., as we have seen, but under the same oouditions alcohol, which is far more volatile than water (i.v. passes more readily iuto the state of vapor), boils at 172-2deg., and ether at 93 - Sdeg., which is more than ■uk'pr. below the normal temperature of the human body, " blood-heat," as it is oallou. — "Good Words."