Chapter VIII: Preface (8)

This is an appreciable factor in the cost of living, but the greatest effectiveness of artificial lighting in curtailing costs is to be found in reducing the fixed charges borne by the product through the operation of two shifts and by directly increasing production owing to improved lighting. The standard of artificial-lighting intensity possessed by the average person at the present time is an inheritance from the past. In those days when artificial light was much more costly than at present the tendency naturally was to use just as little light as necessary. That attitude could not have been severely criticized in those early days of artificial lighting, but it is inexcusable to-day. Eyesight and greater safety from accidents are in themselves valuable enough to warrant adequate lighting, but besides these there is the appeal of increased production.

Outdoors on a clear summer day at noon the intensity of daylight illumination at the earth's surface is about 10,000 foot-candles; in other words, it is equal to the illumination on a surface produced by a light-source equivalent to 10,000 candles at a distance of one foot from the surface. This will be recognized as an enormous intensity of illumination. On a cloudy day the intensity of illumination at the earth's surface may be as high as 3000 foot-candles and on a "gloomy" day the illumination at the earth's surface may be 1000 foot-candles. When it is considered that mankind works under artificial light with an intensity of only a few foot-candles, the marvels of the visual apparatus are apparent. But it should be noted that the eyes of the human race evolved under natural light. They have been used to great intensities when called upon for their greatest efforts. The human being is wonderfully adaptive, but it could scarcely be hoped that the eyes could readjust themselves in a few generations to the changed conditions of low-intensity artificial lighting. There is no complaint against the range of intensities to which the eye responds, for in range of sensibility it is superior to any man-made device.

For extremely low brightnesses another set of physiological processes come into play. Based purely upon the physiological laws of vision it seems reasonable to conclude that mankind should not work under artificial illumination as low as has been considered necessary owing to the cost in the past. With this principle of vision as a foundation, experiments have been made with greater intensities of illumination in the industries and elsewhere and increased production has been the result. In a test in a factory where an adequate record of production was in effect it was found that an increase in the intensity of illumination from 4 to 12 foot-candles increased the production in various operations. The lowest increase in production was 8 per cent., the highest was 27 per cent., and the average was 15 per cent. The original lighting in this case was better than that of the typical industrial conditions, so that it seems reasonable to expect a greater increase in production when a change is made from the average inadequate lighting of a factory to a well-designed lighting-system giving a high intensity of illumination.

In another test the production under a poor system of lighting by means of bare lamps on drop-cords was compared with that of an excellent system in which well-designed reflectors were used. The intensity of illumination in the latter case was twenty-five times that of the former and the production was increased in various operations from 30 per cent. for the least increase to 100 per cent. for the greatest increase. Inasmuch as the energy consumption in the latter case was increased seven times and the illumination twenty-five times, it is seen that the increase in intensity of illumination was due largely to the use of proper reflectors and to the general layout of the new lighting-system.

In another case a 10 per cent. increase in production was obtained by increasing the intensity of illumination from 3 foot-candles to about 12 foot-candles. This increase of four times in the intensity of illumination involved an increase in consumption of electrical energy of three times the original amount at an increase in cost equal to 1.2 per cent. of the pay-roll. In another test an increase of 10 per cent. in production was obtained at an increase in cost equal to less than 1 per cent. of the payroll. The efficiency of well-designed lighting installations is illustrated in this case, for the illumination intensity was increased six times by doubling the consumption of electrical energy.

Various other tests could be cited, but these would merely emphasize the same results. However, it may be stated that the factory superintendents involved are convinced that adequate and proper artificial lighting is a great factor in increasing production. Mr. W. A. Durgin, who conducted the tests, has stated that the average result of increasing the intensity of illumination and of properly designing the lighting installations in factories will be at least a 15 per cent. increase in production at an increased cost of not more than 5 per cent. of the pay-roll. This is apparently a conservative statement. When it is considered that generally the cost of lighting is only a fraction of 1 per cent. of the cost of products to the consumer, it is seen that the additional cost of obtaining an increase of 15 per cent. in production is inappreciable.

Industrial superintendents are just beginning to see the advantage of adequate artificial lighting, but the low standards of lighting which were inaugurated when artificial light was much more costly than it is to-day persist tenaciously. When high intensities of proper illumination are once tried, they invariably prove successful in the industries. Not only does the worker see all his operations better, but there appears to be an enlivening effect upon individuals under the higher intensities of illumination. Mankind chooses a dimly lighted room in which to rest and to dream. A room intensely lighted by means of well-designed units which are not glaring is comfortable but not conducive to quiet contemplation. It is a place in which to be active. This is perhaps one of the factors which makes for increased production under adequate lighting.

Civilization has just passed the threshold of the age of adequate artificial lighting and only a small percentage of the industries have increased their lighting standards commensurately to the possibilities of the present time. If high-intensity artificial lighting was installed in all the industries and a 15 per cent. increase in production resulted, as tests appear to indicate, the increased production would be equal to that of nearly two million workers. This great increase in output is brought about by lighting at an insignificant increase in cost but without the additional consumption of food or clothing. Besides this increase in production there is the decrease in spoilage. The saving possible in this respect through adequate lighting has been estimated for the industries of this country at $100,000,000. If mankind is to have conveniences and luxuries, efficiency in production must be practised to the utmost and in the foregoing a proved means has been discussed.

There are many other ways in which artificial light may serve in increasing production. Man has found that eight hours of sleep is sufficient to keep him fit for work if he has a sufficient amount of recreation. Before the advent of artificial light the activities of the primitive savage were halted by darkness. This may have been Nature's intention, but civilized man has adapted himself to the changed conditions brought about by efficient and adequate artificial light. There appears to be no fundamental reason for not imposing an artificial day upon plants, animals, chemical processes, etc.; and, in fact, experiments are being prosecuted in these directions.

The hen, when permitted to follow her natural course, rises with the sun and goes to roost at sunset. During the winter months she puts in short days off the roost. It has been shown that an artificial day, made by piecing out daylight by means of artificial light, might keep the hen scratching and feeding longer, with an increased production of eggs as a result. Many experiments of this character have been carried out, and there appears to be a general conclusion that the use of artificial light for this purpose is profitable.

Experiments conducted recently by the agricultural department of a large university indicate that in poultry husbandry, when artificial light is applied to the right kind of stock with correct methods of feeding, the distribution of egg-production throughout the whole year can be radically changed. The supply of eggs may be increased in autumn and winter and decreased in spring and summer. Data on the amount of illumination have not been published, but it is said that the most satisfactory results have been obtained when the artificial illumination is used from sunset until about 9 P. M. throughout the year.

An increase of 30 to 40 per cent. in the number of eggs laid on a poultry-farm in England as the result of installing electric lamps in the hen-houses was reported in 1913. On this farm there were nearly 200 yards of hen-houses containing about 6000 hens, and the runs were lighted on dark mornings and early nights of the year preceding the report. About 300 small lamps varying from 8 to 32 candle-power were used in the houses. It was found that an imitation of sunset was necessary by switching off the 32 candle-power lamps at 6 P. M. and the 16 candle-power lamps at 9:30. This left only the 8 candle-power lamps burning, and in the faint illumination the hens sought the roosting-places. At 10 P. M. the remaining lights were extinguished. It was found that if all the lights were extinguished suddenly the fowls went to sleep on the ground and thus became a prey to parasites. The increase in production of eggs is brought about merely by keeping the fowls awake longer. On the same farm the growth of chicks incubated during the winter months increased by one third through the use of electric light which kept them feeding longer.

Many fishermen will testify that artificial light seems to attract fish, and various reports have been circulated regarding the efficacy of using artificial light for this purpose on a commercial scale. One report which bears the earmarks of authenticity is from Italy, where it is said that electric lights were successfully used as "bait" to augment the supply of fish during the war. The lamps were submerged to a considerable depth and the fish were attracted in such large numbers that the use of artificial light was profitable. The claims made were that the supply of fish was not only increased by night fishing but that a number of fishermen were thereby released for national service during the war. An interesting incident pertaining to fish, but perhaps not an important factor in production, is the use of electric lights in the summer over the reservoirs of a fish hatchery. These lights, which hang low, attract myriads of bugs, many of which fall in the water and furnish natural and inexpensive food for the fish.

Many experiments have been carried out in the forcing of plants by means of artificial light. Some of these were conducted forty years ago, when artificial light was more costly than at the present time. Of course, it is well known that light is essential to plant life and in general it is reasonable to believe that daylight is the most desirable quality of light for plants. In greenhouses the forcing of plants is desirable, owing to the restricted area for cultivation. It has been established that some of the ultra-violet rays which are absorbed or not transmitted by glass are harmful to growing plants. For this reason an arc-lamp designed for forcing purposes should be equipped with a glass globe. F. W. Rane reported in 1894 upon some experiments with electric carbon-filament lamps in greenhouses in which satisfactory results were obtained by using the artificial light several hours each night. Prof. L. H. Bailey also conducted experiments with the arc-lamp and concluded that there were beneficial results if the light was filtered through clear glass. Without considering the details of the experiment, we find some of Rane's conclusions of interest, especially when it is remembered that the carbon-filament lamps used at that time were of very low efficiency compared with the filament lamps at the present time. Some of his conclusions were as follows:

The incandescent electric light has a marked effect upon
greenhouse plants.

The light appears to be beneficial to some plants grown for
foliage, such as lettuce. The lettuce was earlier, weighed more
and stood more erect.

Flowering plants blossomed earlier and continued to bloom
longer under the light. The light influences some plants, such
as spinach and endive, to quickly run to seed, which is
objectionable in forcing these plants for sale.

The stronger the candle-power the more marked the results,
other conditions being the same.

Most plants tended toward a taller growth under the light.

It is doubtful whether the incandescent light can be used in
the greenhouse from a practical and economic standpoint on
other plants than lettuce and perhaps flowering plants; and at
present prices (1894) it is a question if it will pay to employ
it even for these.

There are many points about the incandescent electric light
that appear to make it preferable to the arc light for
greenhouse use.

Although we have not yet thoroughly established the economy and
practicability of the electric light upon plant growth, still I
am convinced that there is a future in it.

These are encouraging conclusions, considering the fact that the cost of light from incandescent lamps at the present time is only a small fraction of its cost at that time.

In an experiment conducted in England in 1913 mercury glass-tube arcs were used in one part of a hothouse and the other part was reserved for a control test. The same kind of seeds were planted in the two parts of the hothouse and all conditions were maintained the same, excepting that a mercury-vapor lamp was operated a few hours in the evening in one of them. Miss Dudgeon, who conducted the test, was enthusiastic over the results obtained. Ordinary vegetable seeds and grains germinated in eight to thirteen days in the hothouse in which the artificial light was used to lengthen the day. In the other, germination took place in from twelve to fifty-seven days. In all cases at least several days were saved in germination and in some cases several weeks. Flowers also increased in foliage, and a 25 per cent. increase in the crop of strawberries was noted. Seedlings produced under the forcing by artificial light needed virtually no hardening before being planted in the open. Professor Priestley of Bristol University said of this work:

The light seems to have been extraordinarily efficacious,
producing accelerated germination, increased growth, greater
depth of color, and more important still, no signs of lanky,
unnatural extension of plant usually associated with forcing.
Rather the plants exposed to the radiation seem to have grown
if anything more sturdy than the control plants. A structural
examination of the experimental and control plants carried out
by means of the microscope fully confirmed Miss Dudgeon's
statements both as to depth of color and greater sturdiness of
the treated plants.

Unfortunately there is much confusion amid the results of experiments pertaining to the effects of different rays, including ultra-violet, visible and infra-red, upon plant growth. If this aspect was thoroughly established, investigations could be outlined to greater advantage and efficient light-sources could be chosen with certainty. There is the discouraging feature that the average intensity of daylight illumination from sunrise to sunset in the summer-time is several thousand foot-candles. The cost of obtaining this great intensity by means of artificial light would be prohibitive. However, the daylight illumination in a greenhouse in winter is very much less than the intensity outdoors in summer. Indeed, this intensity perhaps averages only a few hundred foot-candles in winter. There is encouragement in this fact and there is hope that a little light is relatively much more effective than a great amount. Expressed in another manner, it is possible that a little light is much more effective than no light at all. Experiments with artificial light indicate very generally an increased growth.

Recently Hayden and Steinmetz experimented with a plot of ground 5 feet by 9 feet, over which were hung five 500-watt gas-filled tungsten lamps 3 feet above the ground and 17 inches apart. The lamps were equipped with reflectors and the resulting illumination was 700 foot-candles. This is an extremely high intensity of artificial illumination and is comparable with daylight in greenhouses. The only seeds planted were those of string beans and two beds were carried through to maturity, one lighted by daylight only and the other by daylight and artificial light, the latter being in operation twenty-fours hours per day. The plants under the additional artificial light grew more rapidly than the others, and of the various records kept the gain in time was in all cases about 50 per cent. From the standpoint of profitableness the artificial lighting was not justified. However, there are several points to be brought out before considering this conclusion too seriously. First, it appears unwise to use the artificial light during the day; second, it appears possible that a few hours of artificial light in the evening would suffice for considerable forcing; third, it is possible that a much lower intensity of artificial light might be more effective per lumen than the great intensity used; fourth, it is quite possible that some other efficient light-source may be more effective in forcing the growth of plants. These and many other factors must be carefully determined before judgment can be passed on the efficacy of artificial light in reducing the cost of living in this direction. Certainly, artificial light has been shown to increase the growth of plants and it appears probable that future generations at least will find it profitable to use the efficient light-producers of the coming ages in this manner.

Many other instances could be cited in which artificial light is very closely associated with the cost of living. Overseas shipment of fruit from the Canadian Northwest is responsible for a decided innovation in fruit-picking. In searching for a cause of rotting during shipment it was finally concluded that the temperature at the time of picking was the controlling factor. As a consequence, daytime was considered undesirable for picking and an electric company supplied electric lighting for the orchards in order that the picking might be done during the cool of night. This change is said to have remedied the situation. Cases of threshing and other agricultural operations being carried on at night are becoming more numerous. These are just the beginnings of artificial light in a new field or in a new relation to civilization. Its economic value has been demonstrated in the ordinary fields of lighting and these new applications are merely the initial skirmishes which precede the conquest of new territory. The modern illuminants have been developed so recently that the new possibilities have not yet been established. However, artificial light is already a factor on the side of the people in the struggle against the increasing cost of living, and its future in this direction is still more promising.

XIX

ARTIFICIAL LIGHT AND CHEMISTRY

Some one in an early century was the first to notice that the sun's rays tanned the skin, and this unknown individual made the initial discovery in what is now an extensive branch of science known as photo-chemistry. The fading of dyes, the bleaching of textiles, the darkening of silver salts, the synthesis and decomposition of compounds are common examples of chemical reactions induced by light. There are thousands of other examples of the chemical effects of light some of which have been utilized by mankind. Others await the development of more efficient light-sources emitting greater quantities of active rays, and many still remain interesting scientific facts without any apparent practical applications at the present time. Visible and ultra-violet rays are the radiations almost entirely responsible for photochemical reactions, but the most active of these are the blue, violet, and ultra-violet rays. These are often designated chemical or actinic rays in order to distinguish the group as a whole from other groups such as ultra-violet, visible, and infra-red. Light is a unique agent in chemical reactions because it is not a material substance. It neither contaminates nor leaves a residue. Although much information pertaining to photochemistry has been available for years, the absence of powerful light-sources emitting so-called chemical rays in large quantities inhibited the practical development of the science of photochemistry. Even to-day, with vast applications of light in this manner, mankind is only beginning to utilize its chemical powers.

In a portrait studio

ARTIFICIAL LIGHT IN PHOTOGRAPHY]

City waterworks

STERILIZING WATER WITH RADIANT ENERGY FROM QUARTZ MERCURY-ARCS]

Although it appears that the chemical action of light was known to the ancients, the earliest photochemical investigations which could be considered scientific and systematic were those of K. W. Scheele in 1777 on silver salts. An extract from his own account is as follows:

I precipitated a solution of silver by sal-ammoniac; then I
edulcorated (washed) it and dried the precipitate and exposed
it to the beams of the sun for two weeks; after which I stirred
the powder and repeated the same several times. Hereupon I
poured some caustic spirit of sal-ammoniac (strong ammonia) on
this, in all appearance, black powder, and set it by for
digestion. This menstruum (solvent) dissolved a quantity of
luna cornua (horn silver), though some black powder remained
undissolved. The powder having been washed was, for the greater
part, dissolved by a pure acid of nitre (nitric acid), which,
by the operation, acquired volatility. This solution I
precipitated again by means of sal-ammoniac into horn silver.
Hence it follows that the blackness which the luna cornua
acquires from the sun's light, and likewise the solution of
silver poured on chalk, is _silver by reduction_. I mixed so
much of distilled water with the well-washed horn silver as
would just cover this powder. The half of this mixture I poured
into a white crystal phial, exposed it to the beams of the sun,
and shook it several times each day; the other half I set in a
dark place. After having exposed the one mixture during the
space of two weeks, I filtrated the water standing over the
horn silver, grown already black; I let some of this water fall
by drops in a solution of silver, which was immediately
precipitated into horn silver.

This extract shows that Scheele dealt with the reducing action of light. He found that silver chloride was decomposed by light and that there was a liberation of chlorine. However, it was learned later that dried silver chloride sealed in a tube from which the air was exhausted is not discolored by light and that substances must be present to absorb the chlorine. Scheele's work aroused much interest in photochemical effects and many investigations followed. In many of these the superiority of blue, violet, and ultra-violet rays was demonstrated. In 1802 the first photograph was made by Wedgwood, who copied paintings upon glass and made profiles by casting shadows upon a sensitive chemical compound. However, he was not able to fix the image. Much study and experimentation were expended upon photochemical effects, especially with silver compounds, before Niepce developed a method of producing pictures which were subsequently unaffected by light. Later Daguerre became associated with Niepce and the famous daguerreotype was the result. Apparently the latter was chiefly responsible for the development of this first commercial process, the products of which are still to be found in the family album. A century has elapsed since this earliest period of commercial photography, and during each year progress has been made, until at the present time photography is thoroughly woven into the activities of civilized mankind.

In those earliest years a person was obliged to sit motionless in the sun for minutes in order to have his picture taken. The development of a century is exemplified in the "snapshot" of the present time. Photographic exposures outdoors at present are commonly one thousandth of a second, and indoors under modern artificial light miles of "moving-picture" film are made daily in which the individual exposures are very small fractions of a second. Artificial light is playing a great part in this branch of photochemistry, and the development of artificial light for the various photographic needs is best emphasized by reminding the reader that the sources must be generally comparable with the sun in actinic or chemical power. The intensity of illumination due to sunlight on a clear day when the sun is near the zenith is commonly 10,000 foot-candles on a surface perpendicular to the direct rays. This is equivalent to the illumination due to a source 90,000 candle-power at a distance of three feet. The sun delivers about 200,000,000,000 horse-power to the earth continuously, which is estimated to be about one million times the amount of power generated artificially on the earth. Of this inconceivable quantity of energy a small part is absorbed by vegetation, some is reflected and radiated back into space, and the balance heats the earth. To store some of this energy so that it may be utilized at will in any desired form is one of the dreams of science. However, artificial light-sources are depended upon at present in many photographic and other chemical processes.

Although two illuminants may be of the same luminous intensity, they may differ widely in actinic value. It is impossible to rate the different illuminants in a general manner as to actinic value because the various photochemical reactions are not affected to the same extent by rays of a given wave-length. Nearly all human eyes see visible rays in approximately the same manner, but the multitude of chemical reactions show a wide variation in sensitivity to the various rays. For example, one photographic emulsion may be sensitive only to ultra-violet, violet, and blue rays and another to all these rays and also to the green, yellow, and red. Therefore, one illuminant may be superior to another for one photochemical reaction, while the reverse may be true in the case of another reaction. In general, it may be said that the arc-lamps including the mercury-arcs provide the most active illuminants for photochemical processes; however, a large number of electric incandescent filament lamps are used in photographic work.

The photo-engraver has been independent of sunlight since the practical development of his art. In fact, the printer could not depend upon sunlight for making the engravings which are used to illustrate the magazines and newspapers. The newspaper photographer may make a "flashlight" exposure, develop his negative, and make a print from it under artificial light. He may turn this over to the photo-engraver who carries out his work by means of powerful arc-lamps and in an hour or two after the original exposure was made the newspaper containing the illustration is being sold on the streets.

The moving-picture studio is independent of daylight in indoor settings and there is a tendency toward the exclusive use of artificial light. In this field mercury-vapor lamps, arc-lamps, and tungsten photographic lamps are used. Similarly, in the portrait studio there is a tendency for the photographer to leave the skylighted upper floors and to utilize artificial light. In this field the tungsten photographic lamp is gaining in popularity, owing to its simplicity and to other advantages. Artificial light in general is more satisfactory than natural light for many kinds of photographic work because through the ease of controlling it a greater variety of more artistic effects may be obtained. In ordinary photographic printing tungsten lamps are widely used, but in blue-printing the white flame-arc and the mercury-vapor lamp are generally employed. Not many years ago the blue-printer waited for the sun to appear in order to make his prints, but to-day large machines operate continuously under the light of powerful artificial sources. How many realize that the blue-print is almost universally at the foundation of everything at the present time? Not only are products made from blue-prints but the machinery which makes the products is built from blue-prints. Even the building which houses the machinery is first constructed from blue-prints. They form an endless chain in the activities of present civilization.

Artificial light has been a great factor in the practical development of photography and it is looked upon for aid in many other directions. Although there is a multitude of reactions in photographic processes which are brought about by exposure to light, these represent relatively few of the photochemical reactions. In general, it may be stated that light is capable of causing nearly every type of reaction. The chemical compounds which are photo-sensitive are very numerous. Many of the compounds of silver, gold, platinum, mercury, iron, copper, manganese, lead, nickel, and tin are photo-sensitive and these have been widely investigated. Light and oxygen cause many oxidation reactions and, on the other hand, light reduces many compounds such as silver salts, even to the extent of liberating the metal. Oxygen is converted partially into ozone under the influence of certain rays and there are many examples of polymerization caused by light.

Various allotropic changes of the elements are due to the influence of light; for example, a sulphur soluble in carbon disulphide is converted into sulphur which is insoluble, and the rate of change of yellow phosphorus into the red variety is greatly accelerated by light. Hydrogen and chlorine combine under the action of light with explosive rapidity to form hydrochloric acid and there are many other examples of the synthesizing action of light. Carbon monoxide and chlorine combine to form phosgene and the combination of chlorine, bromine, and iodine, with organic compounds, is much hastened by exposing the mixture to light. In a similar manner many decompositions are due to light; for example, hydrogen peroxide is decomposed into water and oxygen. This suggests the reason for the use of brown bottles as containers for many chemical compounds. Such glass does not transmit appreciably the so-called actinic or chemical rays.

There is a large number of reactions due to light in organic chemistry and one of fundamental importance to mankind is the effect of light on the chlorophyll, the green coloring matter in vegetation. No permanent change takes place in the chlorophyll, but by the action of light it enables the plant to absorb oxygen, carbon dioxide, and water and to use these to build up the complex organic substances which are found in plants. Radiant energy or light is absorbed and converted into chemical energy. This use of radiant energy occurs only in those parts of the plant in which chlorophyll is present, that is, in the leaves and stems. These parts absorb the radiant energy and take carbon dioxide from the air through breathing openings. They convert the radiant energy into chemical energy and use this energy in decomposing the carbon dioxide. The oxygen is exhausted and the carbon enters into the structure of the plant. The energy of plant life thus comes from radiant energy and with this aid the simple compounds, such as the carbon dioxide of the air and the phosphates and nitrates of the soil, are built into complex structures. Thus plants are constructive and synthetic in operation. It is interesting to note that the animal organism converts complex compounds into mechanical and heat energy. The animal organism depends upon the synthetic work of plants, consuming as food the complex structures built by them under the action of light. For example, plants inhale carbon dioxide, liberate the oxygen, and store the carbon in complex compounds, while the animal uses oxygen to burn up the complex compounds derived from plants and exhales carbon dioxide. It is a beautiful cycle, which shows that ultimately all life on earth depends upon light and other radiant energy associated with it. Contrary to most photochemical reactions, it appears that plant life utilize yellow, red, and infra-red energy more than the blue, violet, and ultra-violet.

In general, great intensities of blue light and of the closely associated rays are necessary for most photochemical reactions with which man is industrially interested. It has been found that the white flame-arc excels other artificial light-sources in hastening the chlorination of natural gas in the production of chloroform. One advantage of the radiation from this light-source is that it does not extend far into the ultra-violet, for the ultra-violet rays of short wave-lengths decompose some compounds. In other words, it is necessary to choose radiation which is effective but which does not have rays associated with it that destroy the desired products of the reaction. By the use of a shunt across the arc the light can be gradually varied over a considerable range of intensity. Another advantage of the flame-arc in photochemistry is the ease with which the quality or spectral character of the radiant energy may be altered by varying the chemical salts used in the carbons. For example, strontium fluoride is used in the red flame-arc whose radiant energy is rich in red and yellow. Calcium fluoride is used in the carbons of the yellow flame-arc which emits excessive red and green rays causing by visual synthesis the yellow color. The radiant energy emitted by the snow-white flame-arc is a close approximation to average daylight both as to visible and to ultra-violet rays. Its carbons contain rare-earths. The uses of the flame-arcs are continually being extended because they are of high intensity and efficiency and they afford a variety of color or spectral quality. A million white flame-carbons are being used annually in this country for various photochemical processes.

Of the hundreds of dyes and pigments available many are not permanent and until recent years sunlight was depended upon for testing the permanency of coloring materials. As a consequence such tests could not be carried out very systematically until a powerful artificial source of light resembling daylight was available. It appears that the white flame-arc is quite satisfactory in this field, for tests indicate that the chemical effect of this arc in causing dye-fading is four or five times as great as that of the best June sunlight if the materials are placed within ten inches of a 28-ampere arc. It has been computed that in several days of continuous operation of this arc the same fading results can be obtained as in a year's exposure to daylight in the northern part of this country. Inasmuch as the fastness of colors in daylight is usually of interest, the artificial illuminant used for color-fading should be spectrally similar to daylight. Apparently the white flame-arc fulfils this requirement as well as being a powerful source.

Lithopone, a white pigment consisting of zinc sulphide and barium sulphate, sometimes exhibits the peculiar property of darkening on exposure to sunlight. This property is due to an impurity and apparently cannot be predicted by chemical analysis. During the cloudy days and winter months when powerful sunlight is unavailable, the manufacturer is in doubt as to the quality of his product and he needs an artificial light-source for testing it. In such a case the white flame-arc is serving satisfactorily, but it is not difficult to obtain effects with other light-sources in a short time if an image of the light-source is focused upon the material by means of a lens. In fact, a darkening of lithopone may be obtained in a minute by focusing upon it the image of a quartz mercury-arc by means of a quartz lens. In special cases of this sort the use of a focused image is far superior to the ordinary illumination from the light-source, but, of course, this is impracticable when testing a large number of samples simultaneously. Incidentally, lithopone which turns gray or nearly black in the sunlight regains its whiteness during the night.

An amusing incident is told of a young man who painted his boat one night with a white paint in which lithopone was the pigment. On returning home the next afternoon after the boat had been exposed to sunlight all day, he was astonished to see that it was black. Being very much perturbed, he telephoned to the paint store, but the proprietor escaped a scathing lecture by having closed his shop at the usual hour. The young man telephoned in the morning and told the proprietor what had happened, but on being asked to make certain of the facts he went to the window and looked at his boat and behold! it was white. It had regained whiteness during the night but would turn black again during the day. Although pigments and dyes are not generally as peculiar as lithopone, much uncertainty is eliminated by systematic tests under constant, continuous, and controllable artificial light.

The sources of so-called chemical rays are numerous for laboratory work, but there is a need for highly efficient powerful producers of this kind of energy. In general the flame-arcs perhaps are foremost sources at the present time, with other kinds of carbon arcs and the quartz mercury-arc ranking next. One advantage of the mercury-arc is its constancy. Furthermore, for work with a single wave-length it is easy to isolate one of the spectral lines. The regular glass-tube mercury-arc is an efficient producer of the actinic rays and as a consequence has been extensively used in photographic work and in other photochemical processes. An excellent source for experimental work can be made easily by producing an arc between two small iron rods. The electric spark has served in much experimental work, but the total radiant energy from it is small. By varying the metals used for electrodes a considerable variety in the radiant energy is possible. This is also true of the electric arcs, and the flame-arcs may be varied widely by using different chemical compounds in the carbons.

There are other effects of light which have found applications but not in chemical reactions. For example, selenium changes its electrical resistance under the influence of light and many applications of this phenomenon have been made. Another group of light-effects forms a branch of science known as photo-electricity. If a spark-gap is illuminated by ultra-violet rays, the resistance of the gap is diminished. If an insulated zinc plate is illuminated by ultra-violet or violet rays, it will gradually become positively charged. These effects are due to the emission of electrons from the metal. Violet and ultra-violet rays will cause a colorless glass containing manganese to assume a pinkish color. The latter is the color which manganese imparts to glass and under the influence of these rays the color is augmented. Certain ultra-violet rays also ionize the air and cause the formation of ozone. This can be detected near a quartz mercury-arc, for example, by the characteristic odor.

The foregoing are only a few of the multitude of photochemical reactions and other effects of radiant energy. The development of this field awaits to some extent the production of so-called actinic rays more efficiently and in greater quantities, but there are now many practical applications of artificial light for these purposes. In the extensive fields of photography various artificial light-sources have served for many years and they are constantly finding more applications. Artificial light is now used to a considerable extent in the industries in connection with chemical processes, but little information is available, owing to the secrecy attending these new developments in industrial processes. However, this brief chapter has been introduced in order to indicate another field of activity in which artificial light is serving. It is agreed by scientists that photochemistry has a promising future. Mankind harnesses nature's forces and produces light and this light is put to work to exert its influence for the further benefit of mankind. Science has been at work systematically for only a century, but the accomplishments have been so wonderful that the imagination dares not attempt to prophesy the achievements of the next century.

XX

LIGHT AND HEALTH

The human being evolved without clothing and the body was bathed with light throughout the day, but civilization has gone to the other extreme of covering the body with clothing which keeps most of it in darkness. Inasmuch as light and the invisible radiant energy which is associated with it are known to be very influential agencies in a multitude of ways, the question arises: Has this shielding of the body had any marked influence upon the human organism? Although there is a vast literature upon the subject of light-therapy, the question remains unanswered, owing to the conflicting results and the absence of standardization of experimental details. In fact, most investigations are subject to the criticism that the data are inadequate. Throughout many centuries light has been credited with various influences upon physiological processes and upon the mind. But most of the early applications had no foundation of scientific facts. Unfortunately, many of the claims pertaining to the physiological and psychological effects of light at the present time are conflicting and they do not rest upon an established scientific foundation. Furthermore some of them are at variance with the possibilities and an unprejudiced observer must conclude that much systematic work must be done before order may arise from the present chaos. This does not mean that many of the effects are not real, for radiant energy is known to cause certain effects, and viewing the subject broadly it appears that light is already serving humanity in this field and that its future is promising.

The present lack of definite data pertaining to the effects of radiation is due to the failure of most investigators to determine accurately the quantities and wave-lengths of the rays involved. For example, it is easy to err by attributing an effect to visible rays when the effect may be caused by accompanying invisible rays. Furthermore, it may be possible that certain rays counteract or aid the effective rays without being effective alone. In other words, the physical measurements have been neglected notwithstanding the fact that they are generally more easily made than the determinations of curative effects or of germicidal action. Radiant energy of all kinds and wave-lengths has played a part in therapeutics, so it is of interest to indicate them according to wave-length or frequency. These groups vary in range of wave-length, but the actual intervals are not particularly of interest here. Beginning with radiant energy of highest frequencies of vibration and shortest wave-lengths, the following groups and subgroups are given in their order of increasing wave-length:

Röntgen or X-rays, which pass readily through many substances
opaque to ordinary light-rays.

Ultra-violet rays, which are divided empirically into three
groups, designated as "extreme," "middle," and "near" in
accordance with their location in respect to the visible
region.

Visible rays producing various sensations of color, such as
violet, blue, green, yellow, orange, and red.

Infra-red or the invisible rays bordering on the red rays.

An unknown, unmeasured, or unfilled region between the
infra-red and the "electric" waves.

Electric waves, which include a class of electromagnetic
radiant energy of long wave-length. Of these the Herzian waves
are of the shortest wave-length and these are followed by
"wireless" waves. Electric waves of still greater wave-length
are due to the slower oscillations in certain electric circuits
caused by lightning discharges, etc.

The Röntgen rays were discovered by Röntgen in 1896 and they have been studied and applied very widely ever since. Their great use has been in X-ray photography, but they are also being used in therapeutics. The extreme ultra-violet rays are not available in sunlight and are available only near a source rich in ultra-violet rays, such as the arc-lamps. They are absorbed by air, so that they are studied in a vacuum. These are the rays which convert oxygen into ozone because the former strongly absorbs them. The middle ultra-violet rays are not found in sunlight, because they are absorbed by the atmosphere. They are also absorbed by ordinary glass but are freely transmitted by quartz. The nearer ultra-violet rays are found in sunlight and in most artificial illuminants and are transmitted by ordinary glass. Next to this region is the visible spectrum with the various colors, from violet to red, induced by radiant energy of increasing wave-length. The infra-red rays are sometimes called heat-rays, but all radiant energy may be converted into heat. Various substances transmit and absorb these rays in general quite differently from the visible rays. Water is opaque to most of the infra-red rays. Next there is a region of wave-lengths or frequencies for which no radiant energy has been found. The so-called electric waves vary in wave-length over a great range and they include those employed in wireless telegraphy. All these radiations are of the same general character, consisting of electromagnetic energy, but differing in wave-length or frequency of vibration and also in their effects. In effect they may overlap in many cases and the whole is a chaos if the physical details of quantity and wave-length are not specified in experimental work.

In a haberdashery

JUDGING COLOR UNDER ARTIFICIAL DAYLIGHT]

In an art gallery

ARTIFICIAL DAYLIGHT]

It has been conclusively shown that radiant energy kills bacteria. The early experiments were made with sunlight and the destruction of micro-organisms is generally attributed to the so-called chemical rays, namely, the blue, violet, and ultra-violet rays. It appears in general that the middle ultra-violet rays are the most powerful destroyers. It is certainly established that sunlight sterilizes water, for example, and the quartz mercury-lamp is in daily use for this purpose on a practicable scale. However, there still appears to be a difference of opinion as to the destructive effect of radiant energy upon bacteria in living tissue. It has been shown that the middle ultra-violet rays destroy animal tissue and, for example, cause eye-cataracts. It appears possible from some experiments that ultra-violet rays destroy bacteria in water and on culture plates more effectively in the absence of visible rays than when these attend the ultra-violet rays as in the case of sunlight. This is one of the reasons for the use of blue glass in light-therapy, which isolates the blue, violet, and near ultra-violet rays from the other visible rays. If the infra-red rays are not desired they can be readily eliminated by the use of a water-cell.

There is a vast amount of testimony which proves the bactericidal action of light. Bacteria on the surface of the body are destroyed by ultra-violet rays. Typhus and tubercle bacilli are destroyed equally well by the direct rays from the sun and from the electric arcs. Cultures of diphtheria develop in diffused daylight but are destroyed by direct sunlight. Lower organisms in water are readily killed by the radiation from any light-source emitting ultra-violet rays comparable with those in direct sunlight. From the great amount of data available it appears reasonable to conclude that radiant energy is a powerful bactericidal agency but that the action is due chiefly to ultra-violet rays. It appears also that no bacteria can resist these rays if they are intense enough and are permitted to play upon the bacteria long enough. The destruction of these organisms appears to be a phenomenon of oxidation, for the presence of oxygen appears to be necessary.

The foregoing remarks about the bactericidal action of radiant energy apply only to bacteria in water, in cultures, and on the surface of the body. There is much uncertainty as to the ability of radiant energy to destroy bacteria within living tissue. The active rays cannot penetrate appreciably into such tissue and many authorities are convinced that no direct destruction takes place. In fact, it has been stated that the so-called chemical rays are more destructive to the tissue cells than to bacteria. Finsen, a pioneer in the use of radiant energy in the treatment of disease, effected many wonderful cures and believed that the bacteria were directly destroyed by the ultra-violet rays. However, many have since come to the conclusion that the beneficent action of the rays is due to the irritation which causes an outflow of serum, thus bringing more antibodies in contact with the bacilli, and causing the destruction of the latter. Hot applications appear to work in the same manner.

Primitive beings of the tropics are known to treat open wounds by exposing them to the direct rays of the sun without dressings of any kind. These wounds are usually infected and the sun's rays render them aseptic and they heal readily. Many cases of sores and surgical wounds have been quickly healed by exposure to sunlight. Even red light has been effective, so it has been concluded by some that rays of almost any wave-length, if intense enough, will effect a cure of this character by causing an effusion of serum. It has also been stated that the chemical rays have anæsthetic powers and have been used in this rôle for many minor operations.

It is said that the Chinese have used red light for centuries in the treatment of smallpox and throughout the Middle Ages this practice was not uncommon. In the oldest book on medicine written in English there is an account of a successful treatment of the son of Edward I for smallpox by means of red light. It is also stated that this treatment was administered throughout the reigns of Elizabeth and of Charles II. Another account states that a few soldiers confined in dark dungeons recovered from smallpox without pitting. Finsen also obtained excellent results in the treatment of this disease by means of red light. However, in this case it appears that the exclusion of the so-called chemical rays favors healing of the postules of smallpox and that the use of red light is therefore a negative application of light-therapy. In other words, the red light plays no part except in furnishing a light which does not inhibit healing.

Although the so-called actinic rays have curative value in certain cases, there are some instances where light-baths are claimed to be harmful. It is said that sun-baths to the naked body are not so popular as they were formerly, except for obesity, gout, rheumatism, and sluggish metabolism, because it is felt that the shorter ultra-violet rays may be harmful. These rays are said to increase the pulse, respiration, temperature, and blood-pressure and may even start hemorrhages and in excessive amounts cause headache, palpitation, insomnia, and anemia. These same authorities condemn sun-baths to the naked body of the tuberculous, claiming that any cures effected are consummated despite the injury done by the energy of short wave-length. There is no doubt that these rays are beneficial in local lesions, but it is believed that the cure is due to the irritation caused by the rays and the consequent bactericidal action of the increased flow of serum, and not to any direct beneficial result on the tissue-cells. Others claim to cure tuberculosis by means of powerful quartz mercury-arcs equipped with a glass which absorbs the ultra-violet rays of shorter wave-lengths. These conclusions by a few authorities are submitted for what they are worth and to show that this phase of light-therapy is also unsettled.

Any one who has been in touch with light-therapy in a scientific rôle is bound to note that much ignorance is displayed in the use of light in this manner. In fact, it appears safe to state that light-therapy often smacks of quackery. Very mysterious effects are sometimes attributed to radiant energy, which occasionally border upon superstition. Nevertheless, this kind of energy has value, and notwithstanding the chaos which still exists, it is of interest to note some of the equipment which has been used. Some practitioners have great confidence in the electric bath, and elaborate light-baths have been devised. In the earlier years of this kind of treatment the electric arc was conspicuous. Electrodes of carbon, carbon and iron, and iron have been used when intense ultra-violet rays were desired. The quartz mercury-arc of later years supplies this need admirably. Dr. Cleaves, after many years of experience with the electric-arc bath, has stated:

From the administration of an electric-arc bath there is
obtained an action upon the skin, the patient experiences a
pleasant and slightly prickly sensation. There is produced,
even from a short exposure, upon the skin of some patients a
slight erythema, while with others there is but little such
effect even from long exposures. The face assumes a normal rosy
coloring and an appearance of refreshment and repose on
emerging from the bath is always observed. From the
administration of the electric-arc bath there is also noted the
establishment of circulatory changes with a uniform regulation
of the heart's action, as evidenced by improved volume and
slower pulse rate, the augmentation of the temperature,
increased activity of the skin, fuller and slower respiration,
gradually increased respiratory capacity, and diminished
irritability of the mucous membrane in tubercular, bronchitic,
or asthmatic patients. There is also lessened discharge in
those patients suffering from catarrhal conditions of the nasal
passages. In diseases of the respiratory system, a soothing
effect upon the mucous membranes is always experienced, while
cough and expectoration are diminished.