May, 1923
-
INDUSTRIAL A N D ENGINEERING CHEMISTRY
45 1
T h e .Influence of Light on Inorganic Matter and Life Processes By Oskar Baudisch YALEUNIVERSITY, NEW HAVEN,CONN.
cataclysm of the atom. The electrons of the atom, which revolve around a nucleus much as the planets revolve around the F WE WISH to discuss somewhat in detail the influence of sun- sun, are deflected from their original paths into others which light upon inorganic matter and upon living processes, we are more stable but involve less energy. The excess of energy, which is hereby lost to the atom, rushes out into space in the must first get - a clearer idea as to the real nature of light. form of so-called “light quanta.” If a Isaac Newton believed that the sun sends great deal of energy is emitted there is out light in all directions in the form formed ultra-violet light, or even X-ray of infinitesimal particles, which traverse radiation; if the amount of energy emitted space with the velocity of about three hunis not so considerable, infra-red rays are the dred thousand kilometers per second. result. Light, therefore, according t o Newton, was Thus it may be seen that we are apsomething material and the velocity of proaching once more the old Newtonian light resembled that of .atmospheric winds. theory of light, but with the vast difference h-ewton’s emanation theory was combatted that electromagnetic energy, instead of by Huyghens: who opposed to it the much matter, is emitted from the source of light more workable undulation theory of light. in all directions. Huyghens compared the velocity of light, Heretofore we have briefly discussed the not with that of wind, but with that of physicist’s conception of light, and we sound. That which is transmitted by a must now consider what we shall mean by cannon-shot in all directions with uniform a chemical action of light. The answer to velocity is not particles of air, and therethe question is no longer as difficult as it fore of matter, but rather alternate cononce was, since we know that light repdensations and rarefactions-that is to say, a certain state of matter. A familiar analresents a definite form of energy. By a chemical action of light we must inevitably ogy is the phenomenon observed when one mean a change from radiation or light energy The throws a stone into quiet water. to other forms of energy, and it is therematerial particles, in this case particles of Roger Shevmam Studio fore merely a special case of the general water, undergo a stationary vibration, OSXARBAUDISCH transformation of radiation. As long ago whereas to the eve it amears as if there __ were actual translatory motion in all directions. Huyghens as 1818 Grotthus announced the law which asserts that a photochemical change takes place only when the radiation is absorbed was obliged, in order to explain the propagation of light through interstellar spate, to postulate the existence of a new by the body exposed to it. This law is still valid, in spite of all subsequent changes in the different theories of light. Of medium, called ether. course, the light which is absorbed by the body does not have to About the middle of the nineteenth century, Maxwell announced the bold hypothesis that light is an electromagnetic phenom- perform exclusively chemical work. In fact, the absorbed light energy may be changed partly into heat, partly into light enon, and thereby rendered obsolete the old mechanistic theory of diminished energy or into any number of other forms of of light. The success attendant upon Maxwell’s wonderful energy. ideas was astounding. Huyghen’s undulatory theory remained essentially unchanged, except that in place of the ether vibraNATURE OF CHEMICAL CHANGES B R ~ U G H TABOUT BY LIGHT tions, emanating in concentric spherical waves in all directions from the light source, we now have electromagnetic energy. Let us now consider what sort of chemical changes light brings With the aid of Maxwell’s new ideas, the entire field of research about in passing through the earth’s atmosphere. The answer in radiation was enormously extended and we were soon forced to this question which especially interests the chemist is closely to conclude that what had popularly been known as light was connected, as we may now assume, with the formation of organic only a small part of the radiant energy emitted by the sun and from inorganic matter under the influence of light energy. The other heavenly bodies. The electromagnetic theory of light further step in the evolution of life from inorganic matter is will in all probability remain unshaken, but Huyghen’s unduthe one which chiefly interests the biologist. It was first neceslatory or wave theory seems to be in serious danger, owing to sary for the earth to cool down to such an extent that the decertain facts which have been only recently discovered. velopment of organic from inorganic matter might be possible. We have still to discuss very briefly the most modern theory While we can only conjecture as to the temperature a t which of light due t o Planck and Einstein, which invalidates Huyghen’s such development could have taken place, yet it is interesting theory. This new theory is very useful in the explanation of to note the fact observed by the American scientist, Jacques photochemical processes, but so far it has failed to explain certain Loeb, that in hot springs or geysers with a temperature of 55’ C. optical phenomena. The question “What is light?” therefore no algae or other forms of life are present. Therefore, we can is still not completely answered. assume that the earth must have cooled to this temperature According to Planck and Einstein we think of light as that before a living cell could develop. form of pulsating energy which is emitted whenever an atom Logical considerations force the further supposition that disintegrates; or, in other words, light is the result of an internal the constitution of the atmosphere was different in the geologic NATUREOF LIGHT
I
452
INDUSTRIAL A N D ENGINEERING CHEMISTRY
past from what it is to-day. The atmosphere was very rich in carbon dioxide and water vapor, and, in addition to the higher temperature just mentioned, it is probable that those of the sun’s rays which are chemically active-namely, the violet and ultra-violet rays-must have been present to a far greater extent than they are to-day; it is a well-known fact that light sources of higher temperature radiate much more ultra-violet light than those of lower temperature. We can, therefore, on the basis of modern research in physics, chemistry, and geology, get some conception of the conditions existing at that period in the earth’s development, when inorganic matter was changed under the influence of light into living substances. With the help of modern laboratory equipment we can imitate these conditions on a small scale and study the chemical changes which take place. It is unquestionably true that in the geologic past, as a result of violent volcanic eruptions, inorganic salts were largely present in the atmosphere, which doubtless were of great importance in the development of organic matter. For example, in recent volcanic disturbances strongly magnetic, complex salts of iron have been found which contain this metal linked in both the ferrous and ferric conditions. Salts of this constitution are particularly active as catalysts; they also possess the power of activating oxygen and of decomposing water molecules with the formation of hydrogen.
EFFECT UPON INORGANIC MATTER We shall now consider somewhat more exhaustively the chemical changes of the earth’s atmosphere which are brought about by the influence of sunlight. It would be most desirable if we could begin by ascending in an aeroplane as high as possible and analyze chemically the air at this altitude. We shall compromise, however, by ascending the Swiss Alpine peak, Monte Rosa, on the pinnacle of which a small chemical laboratory, at a n altitude of forty-six hundred meters, will simplify our chemical and analytical work. Even on the way to this height, which leads over great glaciers, we notice on our skin the intensive action of the sunlight, and we must cover our faces with thick layers of vaseline to avoid dangerous sunburn. We wear dark glasses t o protect our eyes against blindness from the brillance of the sun. The light of the sun which in the valleys has a beneficent and even healing effect becomes a dangerous enemy when we climb to the altitude of the glaciers. The reason for this lies in the fact that we are continually approaching nearer t o the region of the ultra-violet rays of short wave length, which ultimately would destroy all life. Not only is the direct exposure of the unprotected skin t o the light mortally dangerous, but in addition we are also likely to be slowly poisoned. The air which we breathe in the regions of perpetual ice lying around mountain peaks, such as Mt. Blanc or Monte Rosa, contains considerable quantities of poisonous substances, in particular nitric oxide, nitrous oxide, ozone, hydrogen peroxide, and ammonium nitrite, which change our blood and bring about severe illness. We believe t h a t the so-called “mountain sickness” is partly a result of this kind of poisoning. From investigations which were carried out on the summit of Monte Rosa at an altitude of forty-six hundred meters, it appears that the gases, nitric oxide, nitrous oxide, and ammonium nitrite, which are found in this atmosphere, are decomposition products of a primary product which is extremely unstable and has the composition NOH. The compound NOH, which is called nitrosyl, is not less poisonous than prussic acid, judging by its great reactivity with aldehydes and with iron salts. Nitrosyl or its alkali salts have not yet been isolated in free condition, but we know from the important investigations of Angeli that there is a salt which contains sodium nitrosyl linked with sodium nitrite. With the help of this salt we can study the properties of the extremely unstable free acid called nitrosyl. It
VOl. 15, No. 3
is a special peculiarity of those compounds occurring in nature which are particularly important in the evolution of matter, that as a result of their great reactivity it is impossible to isolate and identify them. To these compounds belongs nitrosyl, which it has been impossible heretofore to secure in the free state. In order to be able to identify such elusive compounds, we resort to a peculiar process, which is known in German as the “Abfangverfahren,” and which consists in trapping or catching the desired compound by means of other substances which are added to the mixture, from which we expect to get the unstable product, and which react extremely easily with it. The famous Italian chemist, Angeli, was the first to observe that nitrosyl reacts with aldehydes t o form so-called hydroxamic acids, which can easily be isolated in the form of complex metal salts. The author and his collaborators used the method just described to separate the nitrosyl, which is formed from air and water by exposure to violet and ultra-violet light radiationthat is, formaldehyde was added to the mixture. The method proved t o be practicable and they were able under suitable experimental conditions to isolate and identify the reaction product of nitrosyl plus formaldehyde-namely, formhydroxamic acid, H-C //NOH
\OH
*
Their method was confirmed by
Baly except that this investigator, instead of using formaldehyde, passed carbon dioxide through an aqueous solution of potassium nitrate. Such solutions when exposed to mercury light form formhydroxamic acid, whereas they are entirely stable in the dark even after being subjected to heat. Finally, if simply an aqueous sdution of carbon dioxide through which air is passed is exposed to radiation it is then not possible to isolate formhydroxamic acid, but by means of chemical reactions i t can be proved that organic compounds containing nitrogen have been formed. By the union of nitrosyl with formaldehyde there is NO formed first of all nitroso methyl alcohol >. As
(:>c
