Man's physical universe

xanabras

406 ENERGY MAY BE PROPAGATED BY VIBRATIONS

practical high-efficiency source thus far produced. The use of pink

" Louverglas" sHghtly reddens the dayhght fluorescent lamp radiations,

thus permitting a still closer approach to natural daylight.

The large light-producing area of fluorescent lamps, the high diffusion

of the light from these lamps, their high efficiency, and low radiant heat

make them very desirable for general illumination; and they have

many excellent supplementary lighting applications.

Ultraviolet Fluorescence Has Many Practical Applications.

The modern "black light" analysis depends upon the fluorescence

or phosphorescence produced in many substances by filtered ultraviolet

radiations.

Certain minerals possess a characteristic fluorescence

under ultraviolet rays, which is useful for means of identification. In

forensic chemistry the ultraviolet rays make it possible to detect

forgeries and alterations in documents.

I n art the authenticity of paintings

and sculptures may be tested because overpainting, patches, etc.

show up at once under ultraviolet rays. Adulteration of foods and

textiles can be discovered by differences in fluorescence. Dead or

artificial teeth do not fluoresce as do natural teeth. The fluorescence of

eggs increases with age.

Hair dyes and oils show up under the fluorescent

light. In a Chicago hospital, babies are "sunburnt" with an

identification mark visible only under ultraviolet rays.

Cigarette stamps made from materials containing quinine will glow

with a blue color in ultraviolet rays, thus differentiating them from

counterfeit stamps which are not fluorescent.

Safety paper containing quinine or uranium salts makes it possible

to detect forgeries readily.

soapsuds, and other materials available to

ultraviolet rays.

Secret messages written with saliva, milk,

prisoners show up under

Phosphorescent wall papers which will glow for a sufficient time to

enable one to avoid hitting his shins against the furniture after turning

out a light are now available.

It was possible to find one's way about in city streets during "blackouts"

in World War II because street signs and direction-markers were

made from fluorescent pigments that glowed in the "black light" from

ultraviolet lights.

Golf tees are now made from a cellulose acetate plastic that contains

a yellow fluorescent pigment, which causes the tees to glow brilliantly

in the sunlight, thus making them easy to find after use.

Ring rot of potatoes, which has invaded 37 states and destroyed

up to 50 per cent of the crop in some localities, is produced by a

germ in the seed potatoes. The infected seed potatoes glow with a

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