' Research and Development in Applied Optics and Optical

Glass at the National Bureau of Standards

A Review and Bibliography

United States Department of Commerce

National Bureau of Standards

Miscellaneous Publication 194

UNITED STATES DEPARTMENT OF COMMERCE • Charles Sawyer, Secretary NATIONAL BUREAU OF STANDARDS • E. U. Condon, Director

Research and Development in Applied Optics and Opt

Glass at the National Bureau of Standards

A Review and Bibliography

By Irvine C. Gardner and C. H. Hahner

National Bureau of Standards Miscellaneous Publication 194

Issued July 15, 1949

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C.

Price 15 cents
Contents

Page

I. Introduction 1 II. Optical instruments and optical systems 2

1. Refractometry 2

2. Range finders 4

3. Lens design 5

4. Photographic lenses 5

5. Optical shop 7

6. Testing of optical instruments and systems 9

7. Services as consultant 10

III. Optical glass 10

1. Slip-casting of clay melting pots 10

2. Effect of composition on the optical properties of glass 11

3. Annealing of optical glass 12

4. Measiu-ement of physical and optical properties of glasses 12

5. Chemical analysis of glass 13

6. Chemical durability of glasses 13

7. Defects in glass 14

8. Transmission of radiant energy 14

9. Consulting and advisory services 15

10. Testing and specifications 15

IV. Bibliography of Bureau publications 15

1. Optical instruments and optical systems 16

(a) Photogrammetry 1 16

(b) Photographic objectives 16

(c) Design and construction of optical instruments 16

(d) Testing and use of optical instruments 16

(e) Miscellaneous papers on optical instruments - 17

(f) Refractometry 17

2. Glass 17

(a) Methods of manufacturing optical glass 17

(b) Effect of composition on optical pi-operties 18

(c) Annealing 18

(d) Measm'ementof physical and optical properties of glasses. 18

(e) Chemical analysis of glass 19

(f) Chemical durability of glasses 19

(g) Transmission of radiant energy 19

(h) Miscellaneous 20

(11)
Development

Optical Glass at the

1 of Standards

Bibliography

and C. H. Hahner

^elopment work in technological optics that Standards. Noteworthy accomplishments

I, 70-inch optical disk (at the time of manuOhio Wesleyan University; a comprehensive

tion and index of refraction of optical glass; erature and index; the design and construcfocal length which resolves railroad ties and

miles; the design and construction of large

Doratory for testing range finders and similar ning to optical glass and optical instruments

is included.

I. Introduction

r Optical instruments include not only those

instruments developed for making observations or measurements within the field of optics but also numerous devices which serve as tools in other

scientific work and for commercial and military

applications. Within the first group, many of

which have found important commercial uses, are

spectrometers, polarimeters, interferometers, re- fractometers, and diffraction gratings. In the

second and much larger group are astronomical

telescopes, microscopes, binoculars, surveying in- struments, motion pictme projectors, airplane camera lenses, bomb sights, and range finders.

All outstanding characteristic of optical instru- ments is the high precision necessary in their

operation. This requires not only extremely accurate design and construction of all optical and

mechanical parts but also the development of

diiferent types of optical glass each having a

specified index of refraction within a very close

tolerance whUe at the same time homogeneous

and free from flaws, chemically and physically

stable, highly transparent, and colorless. The National Bureau of Standards, since its founding in 1901, has carried on a broad program

of optical research and development which has

led to the solution of many problems of interest

to Government agencies and private industry.

This work has included the development of technological processes for the production of optical

glass, the study of the properties of optical materials, the maintenance of optical standards, the

design of lenses and optical systems, the production of prototype optical instruments, the deterniination of performance characteristics, the devising of methods for testuig and calibration,

the preparation of specifications, and complete

consultant service.

In both world wars, the requirements of the

Armed Forces for optical fire-control instruments

resulted in a tremendous expansion in domestic

production of optical glass and optical instruments. Many new instruments, new optical

glasses, and new processes for optical glass manufacture were developed. Indeed, the peacetime

requirements for precision optical instruments are almost negligible in comparison with the need for

military optical instruments in wartime. Moreover, the demands made on industry for the production of nonmilitary optical instruments are

relatively stable, as the required characteristics of

the various instruments do not change greatly

within short periods of time. In military optical

work the reverse is true, and the necessity for

specialized laboratory research is correspondingly

increased.

In view of the apparent need in this country for a continuing, integrated program of research and

development in optica,l science, the National

Bureau of Standards, with the cooperation of the

Armed Services, has conducted a coordinated series of projects basic to the production of all types of

optical instruments, with special emphasis on

military fire-control devices. The National

Bureau of Standards is particularly well fitted to render such service inasmuch as it is the only

scientific institution in the world which has,

entirely within its own organization, complete

facilities for making an optical instrument beginnmg with the raw materials and producing in tm'n
the glass, the optical design, the lenses and prisms,

the mechanical parts, and finally the finished

instrument. The greater part of this higlily specialized work is clone in the Bureau's Optical

Instrument Laboratories, Optical Shop, Glass

Technology Laboratories, and Optical Glass Plant.

However, valuable assistance is frequently re- ceived from sections of the Bureau concerned with

such diverse fields as chemical analysis, refractories, mechanical instruments, photographic technology, interferometry, spectroscopy, radiometry,

photometry, colorimetry, automatic computing,

and electron microscopy.

The scope of the optical program at the National

Bureau of Standards may be indicated by examples

of representative projects. Experience gained in

basic research on the theory and methods of lens

design has been applied in designing a large

number of lenses required by other Government

agencies. The Bm'eau has also established procedures for measuring and specifying the characteristics of photographic lenses, particularly those

used in aerial photography. For the assistance

of industrial and commercial laboratories, methods

of high-precision refractometry were developed,

and standards of refractivity set up. Durmg the

last war, a specially designed laboratory for the

development and testing of range finders was

completed, and other military optical fire-control

instruments, as well as devices for testing them,

have been designed and developed. Very large

optical elements, required for supersonic wind

in the sections which follow, the more important,

phases of the work of the National Bureau of Standards in the fields of optical instrumentation

and optical glass are listed and briefly discussed.

These investigations have led to nearly 200 publications by members of the Bureau staff, which

are given in a bibliography at the end of this paper. References to the bibliography are made

in the text by means of numbers in parentheses.

II. Optical Instruments and Optical Systems

The work at the National Bm-eau of Standards on refractometers, range finders, lens design, and

photogrammetry, because of its extent and importance, will be discussed in special sections which

follow. Investigations of a general nature related

to all optical instruments have involved a study

of resolving power (45) ; the preparation of standard resolving-power charts with instructions for theu' use in testing camera lenses (12, 13); the

publication of detailed instructions for the production of muTors by chemical deposition of

silver on glass (24); and the development of an

interference method, based on the Hartmann test, for determining the aberrations of an optical

system (47, 55).

A niunber of instruments have been developed

for special piu-poses. Among these are an optical

coincidence gage for measuring small distances

(25, 57), an instrument for machining spherical

surfaces of long radius such as are required for grinding and polishing lenses (27, 37), a camera

for photographing the interior of a 30-caliber

service rifle barrel (34, 56), an optical system for

indicating galvanometer deflection (35), spherometers, a camera lucida, a magnifying stereoscope

(4), a field telemeter (32), an anallatic telescope,

and an optical instrument for measuring the wall

thickness of a compressed gas container (36).

i

The Bureau has also built an interferometer with! a 4-inch aperture for testing optical components;

or the homogeneity of optical materials, and

construction of a much larger one is almost complete. Other instruments designed and built ati the Bureau for its own testing needs include a-: special precision camera for testing airplane' camera lenses and cameras (10), an instrumentfor testmg 12-inch plane surfaces interferometri-,

cally over the entire surface at one time, optical

benches (18), an optical spherometer, and many

smaller instruments.

1. Refractometry

The growth of refractometry in the United

States dates from the sudden demand for precise

knowledge concerning the optical constants of the

optical glass (77, 82, 83, 89, 114, 116, 119) thati

2
Figure 1. Coincidence prism.—an important element in range-finder accuracy—constructed by cementing together a number

of smaller prisms made from optical glass produced at the National Bureau of Standards.

The optical range finder, used by tiie Armed Forces to measure the distance from an observer to a target, is one of the most intricate and costly of optical instruments.

was manufactured in and after 1917. Instru- ments for measuring refractive index were soon

being produced in this country; their use increased

rapidly in chemical laboratories and spread to technical applications in the sugar, oil, soap, drug,

paint, ink, food, and other industries. The National Bureau of Standards was then called upon

to test refractometers (81, 85), to formulate

standard performance requirements for these devices, and to measure refractive indices of trans- parent media.

To properly perform these services to industry

and other Government departments, the Bureau

has found it necessary to develop methods of highprecision refractometry (70, 77) in order to establish worldng standards of known refractivity (83).

Use of water as a precise standard liquid in this

work was made possible by measurement of its index of refraction over a broad range of temperature and wavelengths (74, 78, 79, 80).

Chemists engaged in petroleum research identify

and determine the purity of hydrocarbons from

measurements of refractive indices for several

wavelengths. To aid in the attainment of higher

precision and accuracy (81, 85) in such measurements, the Bureau has provided three standai'd

samples of hydrocarbons—2,2,4-trimethylpentane, methylcyclohexane, and toluene—of known

3
FiGtJEE 2. A iemperature-controUed test chamber at the Bureau makes possible the complete analysis of range-finder per- formance under conditions corresponding to a wide range of climate.

The operator, wearing an aviator's insulated suit for work at low temperature, is viewing a simulated target at 90-degree elevation through the oculars of a range

finder under study. Targets at eight apparent ranges for elevations from 0 to 90 degrees are produced by a specially designed collimating system above and behind the range finder. The control board at the operator's right permits changes in range, elevation, and other settings.

high purity, for which the indices of refraction for seven wavelengths are certified to five decimals.

2. Range Finders

The range finder is one of the most complex

optical instruments thus far developed. In this instrument, the number of residual errors which

remain to be corrected is so large, and the individual errors so small and so nearly equal in magnitude, that it is quite impossible to separate

and identify them from observations of terrestrial targets. Therefore, in development work for improvement of range-finder performance, these

residual errors must be studied separately in the

laboratory with adequate control of all envix'onmental conditions such as temperature, exposure

to directed radiation, and orientation with respect

to the gravitational field. The National Bureau of Standards has therefore built a special range-finder testing laboratory

(fig. 2) imder the sponsorship of the Army Ord- nance Department (41). Equipped with a precision collimator system which optically simulates

a target for eight different ranges at any desired

elevation, this laboratory—the only one of its kind in this country—provides for testing under

conditions corresponding to a wide range of cli- mate and permits the complete analysis of the

behavior of a range finder with a thoroughness

and facility impossible with outdoor targets.

To obtain the necessary precision, the apparatus

must produce two collimated beams separated by

the base length of the range finder (13}^ to 15 feet)

and departing from parallelism by an angle dif- fering from a preassigned value by not more than

one-half second. This precision must be independent of large temperature variations and

movements of the apparatus to vary the apparent

elevations of the target. Such rigorous requirements have been met by mounting the collimator

instrument in an insulated chamber which can be

maintained at any fixed temperature between 0°

and 100° F or subjected to a given rate of temperature change. Directed radiation comparable

to that received from the sun under service conditions is simulated by a cylindrical mirror of

paraboloid cross section extending the length of

the range finder. Environmental conditions are thus under complete control at all times.

Range finders of foreign origin and improved

prototype models, as well as those in use by the

Army and Navy, have been tested in the new

laboratory under a wide varietv of conditions (53).
Figure 3. One of the first airplane camera lenses that permitted individual railroad ties la be distinguished at an altitude of 10,000 feet (fig 4).

This //6.3 lens of 50-inch focal length was entirely a product of the National Bureau of Standards, from the manufacture of the glass to the design of the optical system and the construction of its component parts.

As a result of this work, it has been possible to

clarify the many different types of error to which

a range finder is subject (50, 51, 52). Quantitative studies of the errors have led to their correc- tion or compensation. Individual components of

I range finders have been tested separately to deI termine their contribution to over-all performance,

i and improved components having reduced errors have been developed. Range-finder design has

thus been placed on a sound engineering basis,

and the paths along which future development

should proceed have been clearly indicated.

3. Lens Design

Research on the theory and methods of lens

design has been conducted at the National Bureau of Standards for many years (22, 28, 33).

As early as 1927 the Bureau published a 125-page

comprehensive treatment of the algebraic methods

of applying the third-order aberration equations to

lens design (23).

Lens designs required hj other Government

agencies have been provided on reqiiest (29, 31,

I 40). Notable designs completed at the Bureau

I include a telephoto lens system of 20-foot focal

j length and 9-inch aperture for photographing the

I solar corona (38, 39, 68, 69), an //6.3 airplane

j camera lens (fig. 3) of 50-inch focal length, and an

f/5 airplane camera lens of 40-inch focal length.

I The //6.3 lens was one of the earliest airplane camera lenses of World War II which permitted

individual railway ties to be distinguished from

an altitude of 10,000 feet (fig. 4). Among other

Bureau designs are sighting systems for airplane

armament, refracting systems with aspheric surfaces, and Schmidt-type cameras with correcting

plates consisting of a combination of spherical

and aspheric surfaces (42).

4. Photographic Lenses

Immediately after World War I, the Army Air

Corps submitted several captured German airplane camera lenses to the National Bureau of Standards

for investigation (8, 9). Shortly thereafter, the

Government mapping services and the military

agencies became interested in photogrammetric

methods, by means of which both cadastral and

topographic maps can be made from airplane

photographs. From this early beginning until the

present, the importance of this branch of engineering and of the Bureau's participation in it have

continuously increased.

An airplane camera lens, to be suitable for photogrammetric purposes, must have good resolving power and little or no distortion over the

entire field. The Bureau therefore undertook the

development of methods for measuring and

specifving these characteristics (1, 2, 3, 5, 6, 11,

14, 15).

The measurement of distortion in a lens as the

linear displacement of the image point from its distortion-free position—a value convenient for

direct interpretation—was substituted for the

older percentage method of designating distortion

fl8, 19). The Bureau also introduced the practice

of measuring the resolving power of photographic
Figure 4. Photograph made at an altitude of nearly 2 miles with an airplane camera lens (fig. 3) designed and constnicle(\. at the Bureau. On the original 9- by 9-inch print it is possible to distinguish individual railway ties as well as people crossing the street (within circle at upper right).

6
5iises by a photographic method exclusively and

legan expressing the result in terms of lines per

Qillimeter measured on the negative (5, 10).

i'lnally, the calibrated focal length was defined

,nd recommended for use, instead of the equivapnt focal length, with airplane cameras for map

laaking (7). All of these practices have now come

nto general use in the United States and have

peen widely accepted in many other countries.

I The earlier measurements of distortion were

inade on an optical bench, but this method became

Inadequate as the volume of work rapidly in- creased. Furthermore, laboratory tests indicated

[hat the performance of a photograpliic lens must

he studied by a photographic test in order to Eorrelate results with performance in actual use. Wo meet this need, the precision testing camera was

developed and constructed (10). Two negatives

^ made on this instrument, each containing a series

^

'pf 19 exposures, enable distortion, resolving power,

(jistigmatism, and curvature of field to be assessed

I lit five-degree intervals across one diameter of the

I iield of view. At first, this testing camera was

F Equipped with seven collimators, permitting a 60-

'liegree field to be investigated. Later, as widejfingle lenses came into general use, three additional

'bollimators were added so that a 90-degree field

i tould be accommodated.

The increasing interest in photogrammetric

methods has been largely due to the strategic value

[of airplane mapping for military defense. However, the requirements of the Agricultural Adjust-

|nent Administration and of the Soil Conservation

Bervice for prompt delivery of maps of large areas

Iiave also greatly stimulated the establishment of

H'ivilian engineering firms specializing in airplane

j ilphotography and map preparation. This has

iresulted in a need for standard specifications to be

ilused by Government procurement offices in conI tracts with civilian airplane-mapping agencies.

I Such standard specifications, prepared under the

I

' guidance of the Photogrammetric Society of

America, require that bids for Government contracts be accompanied by a National Bureau of

Standards certificate applying to the lens and

I camera which the contractor proposes to use (6). During 1947, 326 cameras and photographic

lenses for photogrammetric work were tested or

certified at the Bureau. Publications have also

been issued dealing with lens testing, lens design,

performance of typical camera lenses, and toleri ances in lens and camera performance for mapping

I purposes (11, 14, 15, 21).

i The work just described has been restricted

almost entirely to lenses for photogrammetric

work. In addition, at the request of the Society of

Motion Picture Engineers, the Bureau has developed a method of calibrating the aperture openings

of a photographic lens in such a way as to compensate for the loss of light by reflection and absorption within the lens (16, 20). It appears probable

831385—49 2

that this system of lens marking will be extended

to all photographic lenses. The departure of the

illumination over the field from the cosine-fourthpower law has also been derived (17), and measure- ments of the variation in illumination introduced

by vignetting have been measured (14, 21).

5. Optical Shop

To aid in the work on optical instruments and

lens design, the National Bureau of Standards

maintains a thoroughly modern Optical Shop

(fig. 5). In general, this shop does not attempt

to utilize production methods but specializes in

making very precise optical components or custom-made optical systems in accordance with

the Bureau's own designs. Lens systems produced by the Optical Shop include the 20-foot

focal length eclipse lens (38) and the//6.3 airplane camera lens of 50-inch focal length (fig. 3) mentioned in the discussion of lens design.

Recently the requirements of wind-tunnel

optics—a new field concerned with wind-turmel

instrumentation for supersonic velocities—have

created a need for large optical components of

extreme precision for use in the interferometers

and schlieren apparatus employed. Glass disks

36 inches in diameter are often required, and even

larger constructions have been contemplated.

The Optical Shop has been called upon to make

large interferometer plates, beam splitters, and

aspheric lenses for this purpose. Off-axis parabolic mirrors, another type of aspheric surface now

important in infrared spectrometry, have also been constructed with diameters up to 8 inches.

As interferometric methods of testing surfaces

and measuring lengths are in general use throughout the Bureau, a large part of the work of the

Optical Shop consists in supplying optical planes

of various sizes and their restoration when they

become badly scratched through use. These

planes are produced with remarkably high precision (67). The graphs in figure 8 show the

departure from planeness of three 11-inch optical

planes of fused quartz which were being worked

at the same time and tested against each other.

Plane No. 12 departs from planeness by not more

than one-hundredth of a wavelength (two ten- millionths of an inch). If this plane were magnified equally in all dimensions so that the diameter were one mile, the departure from planeness would

still be only about one-thousandth of an inch.

The production of optically plane surfaces on

metal requires a teclinique considerably different

from that used with glass. In making a first-order

transit theodolite, an optically plane metal blank

is necessary for the graduated circle if the graduations are to be sufficiently accurate. (Errors

should be no greater than one or two seconds of

arc.) The Optical Shop has devised methods for producing such surfaces and also for bringing the

7
Figure 5. Polishing room in the Bureau's Optical Shop.

This shop does not attempt to use production methods but speciahzes in making very precise optical components or custom-made optical systems in accordance with the Bureau's own design.

]

Figure 6. Centering and edging lens components in the National Bureau of Standards Optical Shop.

After the lens is correctly centered on the rotatinft spindle in the left fore- ground, the two spindles will be interchanged so that the edge of this lens may be ground true on the lai'ge diamond-charged wheel at the operator's

right. Meanwhile, the lens attached to the second spindle, which has

already been centered, is undergoing the edgmg operation. Accuracy of centering is tested by observation of images reflected from the two surfaces

of the lens. Figure 7. A telescope objective must be polished so precisely

that the finished surface does not depart from regularity [ by more than six-millionths of an inch.

This is done in the Bureau's Optical Shop by moans of a rotating pitch surface pressed into the proper curvature and charged with rouge and water. The lens, cemented to a small metal disk, is pressed down against the pitch- covered tool by a pin that fits in a depression in the center of the metal

disk. Lateral motion of the pin support swings the lens back and forth across the tool as it rotates. Rouge and water are applied with a brush between the two surfaces at intervals. Note that the surface of the pitch is ! marked off into squares by grooves which receive excess polishing materials.
\ locating shoulders of a graduated circle into optical

parallelism with the surface to be graduated,

i During World War II the Army Engineer Board

i undertook the development of a precision transit

j of the European type with graduated circles not

i, more than 4 inches in diameter. The Optical

I Shop produced the metal blanks for the circles

j used in the earlier instruments and also made the

! glass blanks required for the later models.

The making of graduated circles is an instance

where the precision obtained in optical tests and

methods of working optical surfaces is utilized to produce parts for other than optical applications.

Other examples from the work of the Optical

Shop are high-precision decimeters and other

i length standards of fused quartz, accurate cores

for inductances, and precise spheres to serve as standards of curvature. Each different crystalline material requires a

special technique for the production of an optically

regular surface and a good optical polish. At

present a large number of new synthetic crystals

are becoming increasingly important because of

their refraction or transmission characteristics,

and the development of suitable techniques for polishing them is a matter of special study at the

Bureau.

+.05 X

PLANE NUMBER 10

+.05 Xr

PLANE NUMBER 1

1

+.05Xr

"•"'^ PLANE NUMBER IE Figure 8. Profiles of three standard planes of fused quartz

that were made in the Bureau's Optical Shop.

Interference methods show the departure from planeness cff plane 12 to be

less than two one-huAdredths of a wavelength of light, i e., less than onehalf of a millionth of an inch. The planes are WH inches in diameter and

2 inches thick.

6. Testing of Optical Instruments and Systems

Military Ojjtical Fire-Control Instruments. In

addition to the range finder program (30, 41, 53),

the National Bureau of Standards has done much

work on optical fire-control instruments (66).

This has included investigations of the Sperry and

Norden bomb sights and the development of

instruments for testing gun sights to be used on

Figure 9. An optical instrument designed at the Bureau

to test the accuracy of gun sights for the Air Force.

airplane-mounted machine guns (fig. 9), as well as the actual design and development of sights for aircraft armament.

General Testing. The National Bureau of

Standards also does a large amount of general

testmg of optical instruments for the public and

for other Government agencies (43). Examples are: determmations of focal length for all types of

lenses, measurements of the power and freedom

from defects of spectacle lenses, and determinations of the optical characteristics of surveying

instruments. The results often serve as criteria for acceptance or rejection of instruments being

purchased by Government agencies. In other

instances calibration curves are provided for use

in obtaining corrections to indicated readings.

Occasionally, data for special types of apparatus

are of sufficiently general interest to justify their

separate publication (48, 49).

Specifications jor Optical Instruments. The

Federal Specifications Board, the American Standards Association, the National Military Establishment, the Society of Motion Picture Engineers, the

International Commission on Illummation, and

the International Commission on Optics are among those organizations which have a continuing interest in the standardization of optical

nomenclature and units and in the preparation of specifications to govern the purchase of optical

products and optical instruments. The National

Bureau of Standards is represented hi all such

committee work, and its staff members devote a

considerable portion of their time to obtaining the

necessary information and formulating it into the

jDroper form for the reports of these organizations.

9
7. Services as Consultant

The National Bm*eau of Standards provides

general consulting services to other Government

agencies on matters relating to the use and design

of optical instruments. Consultations cover a wide

range of subjects, including high-speed cameras for the National Advisory Committee for Aeronautics;

large interferometers for the Air Force, the Navy,

and the Army Ordnance Department; precise

mapping cameras for the Geological Survey, photographic lenses and surveying instruments for the

Coast and Geodetic Survey; motion picture projectors for the Bureau of Federal Supply, Treasiu-y

Department; and microfilm readers for the Army.

As these agencies do not, in general, have sufficient optical work to maintain a permanent staff of optical specialists, they find the services of the

Bm'eau most convenient.

The National Bureau of Standards is also required "to supply available information to the

public upon request, in the fields of physics, chemistry, and engineering." Individuals and business

firms constantly are asking for assistance. They

are fm-nished information on specific optical

subjects or given reference to other sources of information.

III. Optical Glass

Optical glass, an indispensable raw material for precision optical instruments, has been developed

and produced by. the National Bureau of Standards

ever since World War I, when the lack of available

manufacturing facilities and scientific knowledge in

this field combined to expand the Bm-eau's newly

established experimental glass plant into a manufacturing unit. With the production of optical

glass in large quantities, it became necessary to provide for the prompt measurement of samples

of glass from the large melts and also from the numerous experimental melts that were made.

Tolerances for the quality of optical glass were

formulated, and methods of test were worked out

for determination of strain, striae, and other

defects. During this period the immersion tests were devised which permit testing of glass for

striae without preliminary grinding and polishing.

This method greatly simplified control and was of

material aid in development and production of new glasses. It was followed by a procedure for measuring the index of refraction of glass in irregularly shaped pieces.

At the end of World War I the American optical

glass industry was allowed to decline, most

manufacturers ceasing production entirely. However, from 1919 to 1939 the Bureau's optical glass

laboratories were maintained for research and

small-scale production. This, along with the

output of the Bausch & Lomb Optical Co., was

the extent of optical glass manufacture in the

United States over that period. Probably the

best known achievement during these years was

a 70-inch optical disk successfully completed at the Bureau in 1928 for the telescope of the Perkins

Laboratory, Ohio Wesleyan University. At that

time the disk represented the largest optical

clement ever made in this country. No American

commercial manufacturer was then willing to undertake the casting and annealing of so large a blank for astronomical purposes.

World War II brought greater demand for optical instruments than ever before, with con- sequent heavy requii'ements for optical glass, and

the Bureau's experimental glass plant was put

into full-scale operation. From this nucleus, with

greatly expanded facilities and increased personnel,

it became one of the small group of plants supplying this country's optical glass needs. Production ^ of optical glass at the Bureau increased from 8,000

pounds in 1938 to a peak of 236,000 pounds in 1943.

At the beginning of the war six kinds of optical

glass were being made at the Bureau; during the ^ war this was increased to 28 types. For some of these which had been made previously, published f information was available on compositions, an- i nealing temperatures, and other physical prop- j erties so that little experimental woi'k was neces- sary before satisfactory glasses could be produced. [ In other cases entirely new types, on which little

' or no data previously existed, were developed in i the laboratory and then put into full-scale pro- ji duction. Early in the war, representatives of t the Canadian and Australian governments visited ji the Bureau's gjass laboratories to study methods p and equipment. As a result, plants were estab- ( lished and producing optical glass in each of these f countries by 1941. Technical assistance was also |< given to several manufacturers in the United I States who were thus able to begin production in |i a remarkably short time, although they had had |i no previous experience in optical glass manufac- 1 ture. With the end of the emergenc}^, the optical t glass program at the Bureau again returned to

j pilot plant-scale operations and to research on 1 new glass compositions, methods of making glass,

and measurement of its physical and chemical | properties.

t 1. Slip-Casting of Clay Melting Pots | One of the major problems in manufacturing i optical glass is the making of the melting pots } (fig. 10). Good-quality glass requires pots that '* will not introduce impurities through reaction } with molten glass.

10
Figure 10. Clay -pots and stirring thimbles used in melting

optical glass.

These pots are produced by means of a slip-casting process developed at the Bureau to meet the need for pots that would not react with molten glass. This process replaced the hand-molding methods previously used in making clay pots.

To meet this need, the Bureau's Refractories

Laboratory developed a process for making pots

by slip-casting to replace laborious hand-forming

methods (88). This process has been widely used,

and cast pots have now largely supplanted handmade pots, not only in optical glass plants but in plants manufacturing glass for other purposes.

At the same time it was found that the pots could

be produced entirely from domestic ball clays and

kaolins. A number of improvements were later introduced, such as lining the pot with less per- meable material. Although there have been some

changes in composition, the basic process has

remained the same (91, 92, 95, 96, 99, 100).

2. Effects of Composition on the Optical Properties of Glass

An important phase of optical glass research at

the National Bureau of Standards has been the

development of new glasses with unusual optical

properties. Optical designers particularly desire

glasses having a ratio of index of refraction to dispersion different from that for standard types.

Although a number of glasses of this sort have

been made available within recent years, many

more are needed. However, their development

will require extensive research since they must not

only have the desired optical properties but must

be adaptable to large-scale manufacture.

When a new type of glass is required, its tentative composition is first formulated on the basis

of the known effects of the various constituents on optical properties, such as index of refraction

and dispersion. A trial melt of about 50 grams

is made, and measurements are taken of index

of refraction, dispersion, liquidus temperature

(Fig. 11), softening point, stability of the glass,

and other characteristics. Melts on a pilot-plant

scale may then be undertaken. However, on this

scale such factors as volatilization rate and pot

solution become important. As a result, the first large-scale melt is seldom satisfactory, and often

several trials are necessary before appreciable

quantities of suitable glass are obtained.

In this work the glass technologist must co- operate closely with the instrument designer. It

is also essential that he know the effect of each

chemical element on the index of refraction and on

dispersion. These relations have been the subject of numerous investigations at the National

Bureau of Standards (104 to 108). While several

theories have been advanced which permit calculation of the index of refraction and dispersion from

composition, the results are not always accurate if extrapolations are made into fields of compositions

that differ widely from those in which the data were taken. For this reason, new fields of compositions must be explored thoroughly before

accurate predictions can be made as to the

Figure 11. A sample of optical glass produced in the Bureau's experimental glass plant is introduced into a tubular electric furnace designed for study of the liquidus

temperature and crystallization rate of the glass.

In the new fields of glass composition now under study at the Bureau, data on

these properties are highly important, since glasses that crystallize readily cannot be made in large pieces.

11
compositions which will give the desired optical constants. Optical glass must also have satisfactory durability if it is to be used widely either in military or in scientific instruments. Moreover, glasses

that devitrify readily cannot be made in large

pieces since crystals would form before the piece

could be cooled. Thus, in new fields of glass compositions now under study at the Bureau (108)

data on liquidus temperature and i-ato of crystal

growth are important.

3. Annealing of Optical Glass

As glass passes from the liquid to the vitreous

solid state, strains are set up within the body of the glass. These strains, which seriously affect

its physical as well as optical properties, are re- moved by annealing. In the process of annealing,

the glass is heated to a temperature just short of

its softening point, held at this temperature long

enough to remove the strains, and then cooled

gradually.

The annealing of optical glass is one of the mostj

important, and at the same time one of the most!

critical, processes in its production. When properly annealed, an optical element should be free from]

strain and of uniform refractive index throughout,

and the final polished surfaces should not distortl with time. As the index of refraction of glass is aft'ected by its annealing temperature, an exact knowledge of the relation between these two

quantities is necessary. Valuable contributions to the knowledge of the changes that take place in|

glass when it is annealed have been made by A.

Q. Tool and other members of the staft' of the! National Bureau of Standards (109 to 117, 120| to 127).

4. Measurement of Physical and Optical Properties of Glasses

Measurement of the physical and optical

properties of glasses has been an important part

of the work of the National Bureau of Standards.

These properties are of interest because they conFiGURE 12. A pot of molten glass is removed Jrom one of the melting fur7iaces in the Bureau's Optical Glass Plant.

Temperatures in the neighborhood of 1 ,400° C are required for fusion of the sand and other ingredients into a homogeneous transparent material.

12
r

it Figure 13. Slow cooling of molten optical glass produces

i I large chunks, which are removed by breaking open the

, melting pot.

These chunks are then cut into smaller pieces from which lenses and prisms

are made.

jtribute to an understanding of the basic nature

;and structure of glass, and because they provide

information for the manufacture and intelligent

utilization of this important substance. One of

the earliest reports on this work was that of Peters and Cragoe (130) on the thermal dilatation

j of glass. The interferometer method which they

I used has proved to be one of the most satisfactory

procedures for measuring the thermal expansion

of glass at high temperatures. The method has

been further refined by Saunders (139, 142), and

an instrument for continuous recording of the data on a photographic film has been developed.

vStudies of the effect of various glass-making

oxides on expansion, annealing point, and softening point have also been made by a number of

investigators.

The viscosity and surface tension of glass, as modified by composition and other variables, are

of great interest since these properties affect the

melting and forming of hot glass. Significant

work in this field has been done by members of

the Bureau staff (136, 143, 145).

5. Chemical Analysis of Glass

j Because the chemical analysis of glasses has

I been a time-consuming operation, it has often

I been avoided. Much of the literature on glass is

I thus of limited value because the exact composii tions of the glasses studied are unknown. In

I many cases manufacturers have not had an exact knowledge either of the chemical composition of

the raw material they were using or of the finished

glass. Rapid and accurate methods of cheniical

analysis are therefore of great interest to glassmakers. A number of improved analytical

methods developed at the National Bureau of

Standards (146 to 153) have found widespread

use in the industry.

Another important aid to analytical chemistry

has been the maintenance of standard samples of

glasses, of sand and other raw materials, and of a number of refractory bodies. These samples

have been prepared for checking the accuracy of

methods of analysis and may be purchased at a nominal fee. As even the more rapid analytical methods

require an excessive amount of tim.e, glass compositions are often calculated from measurements

of density or index of refraction. While such

methods cannot accurately determine composition

without other background information, they can

be very useful tools in process control. In fact,

if conditions are such that only one or two in- gredients in a glass batch are subject to variation

(as by volatilization or solution of refractory),

calculation of quantities of major constituents

from physical measurements may give more

accurate results than chemical analysis.

The Bureau's work on variations of density

and index of refraction with composition (104 to 108) gives much of the information necessary to make such calculations. However, since these

properties depend upon the heat treatment re- ceived, the glasses must be annealed to prescribed

conditions before thev can be properly measiu-ed.

A number of papers (110, 112, 113, 114, 115, 117,

120, 121, 123, 124, 125, 126, 127) deal with the

variation of physical properties of glasses with

heat treatment.

6. Chemical Durability of Glasses

While glass is usually highly resistant to chemical attack, yet glasses do undergo chemical

changes which may be very slow or quite rapid,

depending upon composition and conditions of

exposure (154 to 168). Optical glasses, especially

those used in military instruments, must withstand moistiu'e, carbon dioxide and other gases, and fungus growth. Resistance to chemical

action is also important in laboratory glassware

and in glass containers for pharmaceutical

preparations.

Because of the widespread interest in methods

of measuring the chemical durability of glasses, the

National Bureau of Standards has been active for many years in developing such tests. This program has involved not only practical procedures

for measuring durability (154, 155, 156, 157, 158,

160, 162, 164, 165), but also more fundamental

work on the mechanism of chemical attack and

the nature of the chemical reactions that take place

at glass-liquid or glass-air interfaces (161, 165,

166, 167, 168).

I
Figure 14. Large pieces of optical glass produced in the Bureau's Optical Glass Plant. The glass is sawed with a diamond saw into sizes convenient for molding into blanks from which lenses, prisms, and optical flats can be made.

Figure 15. A step in the preparation of an optical blank

in the Bureau's Optical Glass Plant.

The rough glass chunk is heated on the end of a punty rod in the furnace (backcround), then rolled into cylindrical form. In the next operation

it is cut ofT into a metal mold, and pressed to shape.

7. Defects in Glass

Because of its intimate contact with glass manufacturers and other branches of the ceramic industry, the National Bureau of Standards has been

able to add much to the Icnowledge of the reactions

that take place between molten glass and refrac- tory melting pots (183, 184, 186, 189). Closelyi

allied to these investigations has been a study of i the crystalline material which may form either by

reaction of the glass with the refractory or within ] the molten glass itself (181, 182, 185, 188, 190,

192).

8. Transmission of Radiant Energy

The National Bureau of Standards has made i transmission measurements of a number of glasses \ used for protecting the eyes from injurious radiation (169, 176). The effects of many different'

ingredients on transmittance of the glass have also been investigated. Of particular importance has i been the transmittance in the ultraviolet and

infrared region of the spectrum (169 to 176 and

178).

14
9. Consulting and Advisory Services

Another important part of the Bureau's work

on glass is the consulting service furnished to other

Government departments. Many requests are

received for technical information on optical glass,

safety glass, chemical durability of glass, and

specifications and tests. Information on specific

topics relating to glass is also given to the general

public upon request.

10. Testing and Specifications

The National Bureau of Standards has been

active in the development of methods for testing

glass and glassware, and in preparing specifications

for a number of glass products. Much of this

work has been done in cooperation with manufacturers and users tlirough organizations such as the American Society for Testing Materials and

the American Standards Association. The Bureau

has also been represented on the committees that

have prepared Federal Specifications for glass

items of interest to the Government.

Figure 16. Three stages in the production of an optical prism at the National Bureau of Standards.

The blank is cast (left) of size larger than required in order to permit the removal of all irregularities. Tt is then ground to very nearly the desired dimensions

(center) before final polishing to produce the finished optical element (right).

IV. Bibliography of Bureau Publications

The publications of the National Bureau of Standards are intended to record those phases of an activity that are of general interest and permanent value. Listed below are 195 publications

by members of the Bureau staff in the fields of optical instrumentation and glass technology;

however, a large number of reports on these subjects, which were circulated as classified material

during the last war, are not included.

Where prices are shown for publications issued

by the Bureau, they may be purchased from the

I Superintendent of Documents, U. S. Government

i Printing Office, Washington 25, D. C. Where

prices are omitted for Bureau publications they

are out of print, but may be consulted in libraries

maintaining reference sets of Bureau publications.

A complete catalog of Bureau publications, 1901

to June 30, 1947, with author and subject indexes,

NBS Circular C460, is available from the Superintendent of Documents for 75 cents. Copies of articles published in the technical

journals referred to are not obtainable from the

Government. They may be consulted in technical libraries maintaining reference sets of such

periodicals, or requests should be sent direct to the publisher.

The following letter-sj^mbol designations are used in this paper for Bureau publications, and

these letters should be included with the serial number in all references to Bureau publications.

S, Scientific Papers.

'

T, Technologic Papers.

RP, Research Papers.

C, Circulars.

H, Handbooks.

M, Miscellaneous Publications.

CS, Commercial Standards.

LC refers to mimeographed pamphlets designated "Letter Circulars," single copies of

which may be obtained free from the

Bureau so far as copies are still available.

15
1. optical Instruments and Optical Systems

(a) Photogrammetry

(1) Optical requirements of airplane mapping. I. C. Gardner. BS J. Research 8, 445 (1932) RP427. lOfi (2) Relation of camera error to photogrammetric mapping. I. C. Gardner. J. Research NBS 22, 209

(1939) RP1177.

(3) Locating the principal point of precision airplane

mapping cameras. F. E. Washer. J. Research

NBS 27, 405 (1941) RP1428. 10^

(4) A magnifying stereoscope and camera lucida: two

instruments for airplane mapping. I. C. Gardner.

J. Opt. Soc. Am. & Rev. Sci. Instr. 11, No. 2,. 195

(1925).

(5) The interpretation of lens tests and camera calibrations. I. C. Gardner. Photogrammetric Engineering 3, No. 1, 13 (1937).

(6) Specifications for a precision mapping camera. I. C. Gardner. Photogrammetric Engineering 4, No. 3, 173 (1938).

(7) The significance of the calibrated focal length. I. C. Gardner. Photogrammetric Engineering 10, No.

1, 22 (1944).

(b) Photographic Objectives

(8) Axial aberrations of lenses. E. D. Tillver and H. I. Shultz. Bui. BS 14, 341 (1918-19) S311.

(9) Aberrations of long focus anastigmatic photographic

objectives. A. H. Bennett. Sci. Pap. BS 19, 587 (1923-24) S494.

(10) Precision camera for testing lenses. I. C. Gardner

and F. A. Case. J. Research NBS 18, 449 (1937) RP984. 10^

(11) Resolving power and distortion of typical airplane- camera lenses. F. E. Washer. J. Research NBS

22, 729 (1939) RP1216.

(12) Charts for testing lens resolution. NBS Miscel- laneous Publication M166 (1940).

(13) A test of lens resolution for the photographer. I. C. Gardner. NBS Circular C428 (1941). 50^

(14) Characteristics of wide-angle airplane-camera lenses. F. E. Washer. J. Research NBS 29, 233 (1942)

RP1498. 5(5 (15) Region of usable imagery in airplane-camera lenses. F. E. Washer. J. Research NBS 34, 175 (1945)

RP1636..10^

(16) Compensation of the aperture ratio markings of a photographic lens for absorption, reflection, and

vignetting losses. I. C. Gardner. J. Research

NBS 38, 643 (1947) RP1803. 10^

(17) Validity of the cosine-fourth-power law of illumination." I. C. Gardner. J. Research NBS 39, 213

(1947) RP1824. lOfi (18) The distortion of some typical photographic objectives. A. H. Bennett. J. Opt. Soc. Am. & Rev.

Sci. Instr. 14, No. 3, 235 (1927).

(19) The compensation of distortion in objectives for air- plane photography. I. C. Gardner and A. H.

Bennett. J. Opt. Soc. Am. & Rev. Sci. Instr. 14, No. 3, 245 (1927).

(20) Compensation of the aperture ratio markings of a photographic lens for absorption, reflection, and

vignetting losses. I. C. Gardner. J. Soc. Mot.

Pict. Eng. 49, 96 (August 1947).

(21) Lenses of extremely wide angle for airplane mapping.

I. C. Gardner and F. E. Washer. J. Research

NBS 40, 93 (1948) RP1858, 10?;; J. Opt. Soc. Am.

38, No. 5, 421 (1948).

(c) Design and Construction of Optical Instruments

(22) Spherical aberration in thin lenses. T. T. Smithj „, Sci. Pap. BS 18, 559 (1922-23) S461. j" (23) Application of the algebraic aberration equations to

optical design. I. C. Gardner. Sci. Pap. BS 22,1 , 73 (1927-28) S550.

(24) Making of mirrors by the deposition of metal on glass. NBS Circular C389 (1931). 10^ . (25) Optical coincidence gage. I. C. Gardner and F. A.f Case. BS J. Research 6, 229 (1931) RP272. ' (26) Reciprocal spherical aberration of an optical system

including higher orders. Harold F. Bennett. BS' . J. Research 9, 187 (1932) RP466. 5^ ( (27) Attachment for turning approximateh' spherical sur-j faces of small curvature on a lathe. I. C. Gardner.' ,,, BS J. Research 9, 227 (1932) RP467. f ^> (28) Compound lens svstems. T. Townsend Smith. J.' Opt. Soc. Am. 1, No. 4, 113 (1917).

(29) The cemented telescope objective of barium crownP and flhit. I. C. Gardner. J. Opt. Soc. Am. 4, No. 5, 275 (1920). p *

(30) The coincidence tvpe of self-contained range finder, i I. C. Gardner. " J. Opt. Soc. Am. 5, No. 5, 420 1 ,. (1921). P'l (31) Constructional data for a cemented objective ofi barium crown and flint. I. C. Gardner. J. Opt.' Soc. Am. & Rev. Sci. Instr. 6, No. 4, 379 (1922).

^

(32) A field telemeter for approximate surveying. I. C.' Gardner. J. Opt. Soc. Am. & Rev. Sci. Instr. 6,f

* No. 5, 489 (1922).

(33) Image curvature as a function of diaphragm position, r' "

I. C. Gardner and J. J. Arnaud. J. Opt. Soc. Am.' & Rev. Sci. Instr. 9, No. 6, 675 (1924).

(34) A camera for photographing the interior of a rifle barrel. I. C. Gardner and F. A. Case. J. Opt. ' 55 Soc. Am. & Rev. Sci. Instr. 12, No. 2, 159 (1926).

^ (35) An optical system for reading the angular deflection ; 59 of a mirror. I. C. Gardner. J. Opt. Soc. Am. <fe

' Rev. Sci. Instr. 12, No. 5, 529 (1926). 1 (36) Optical methods for testing compressed gas containj jj ers. I. C. Gardner. Fourteenth Ann. Rep., 1926,

Compressed Gas Manufacturers' Assn., Inc. 24 f 51 (Jan. 1927).

(37) Spherical surfaces of slight curvatures. I. C. Gardner. I Am. Machinist 76, 994 (Sept. 1932). | (38) Design and construction of eclipse apparatus. Narrative of the expedition (National Geographic ' Society-National Bureau of Standards Eclipse Ex- ji 'gj pedition of 1940). I. C. Gardner. National Geographic Societv, Contributed Technical Papers, j Solar Eclipse Series, No. 2, p. 4 and 95 (1942). \yt (39) The National Geographic Society-National Bureau of Standards Eclipse Expedition of 1940. I.' C.

j Gardner. Proceedings of the Eighth American , Scientific Congress, vol. VII, page 77 (1942). t ,5 (40) The design of triplet anastigmat lenses of the Taylor

' tvpe. R. E. Stephens. J. Opt. Soc. Am. 38, No. j » 12, 1032 (1948).

(41) A range finder testing laboratorv. I. C. Gardner, j J. Applied Physics 19, 721 (1948). ] j (42) Reduction of spiiero-cliromatic aberration in catadioptric systems. R. E. Stephens. J. Research , NBS 40," 467 (1948) RP1892, 5(5; J. Opt. Soc. Am.

38, 733 (1948).

(d) Testing and Use of Optical Instruments

(43) Testing and properties of optical instruments. NBS

Circular C27 (1911). ( (44) New method of determining the focal length of a

converging lens. I. G. Priest. Bui. BS 5, 483 4 [ (1908-09) SllO.

(45) Resolving power of objectives. P. G. Nutting. Bui. i BS 6, 121 (1909-10) S122. i (46) Micrometer microscopes. A. W. Grav. Bui. BS 10, • 375 (1914) S215.

16
(47) Interference method for the determination of axial

' and oblique aberrations. A. H. Bennett. BS J. Research 2, 685 (1929) RP52.

(48) Lateral chromatic aberration of apochromatic microscope systems. I. C. Gardner and F. A. Case. BS J. Research 6, 937 (1931) RP316. 5i4 (49) Optical and mechanical characteristics of 16-milliI meter motion-picture projectors. R. E. Stephens,

j NBS Circular C437 (1942). 10^

|(50) Precision of telescope pointing for outdoor targets,

i F. E. Washer and H. B. Williams. J. Research

NBS 36, 479 (1946) RP1717; J. Opt. Soc. Am. 36,

I 400 (1946).

K.51) Effect of magnification on the precision of indoor

telescope pointing. F. E. Washer. J. Research

NBS 39, 163 (1947) RP1820. lO^i

|(52) Influence of the atmosphere upon the precision of telescope pointing. F. E. Washer and L. W. Scott.

I J. Research NBS 39, 297 (1947) RP1829. 10(^

1(53) The testing of range finders. I. C. Gardner. J.

' Applied Physics 19, 729 (1948).

j(54) Apparatus for the testing of binocular telescopes. T. Townsend Smith. J. Opt. Soc. Am. 2-3, Nos.

3-6, 76 (1919).

(55) A modified Hartmann test based on interference.

I. C. Gardner and A. H. Bennett. J. Opt. Soc. Am. & Rev. Sci. Instr. 11, No. 4, 441 (1925).

Zeitschrift fur Instrumentenkunde 47, 197 (1927) Translation.

j(56) Photographing the bore of a rifle. I. C. Gardner.

I The Military Engineer 18, No. 102. 480 (1926).

i(57) An optical coincidence gage. I. C. Gardner. Am.

Machinist 74, 155 (1931).

(e) Miscellaneous Papers on Optical Instruments

(58) Specifications for marine sextants. NBS Circular Clio (1921).

(59) Representation of aberration diffraction effects by

means of rotating sectors. A. H. Bennett. BS J. Research 3, 391 (1929) RP102.

(60) "Camera finish" at the race track. I. C. Gardner.

J. Research NBS 18, 467 (1937) RP986. 5<li (61) Radiometry; publications by the staff of the National Bureau of Standards. NBS Letter Circular LC635 (1941).

(62) Colorimetry and spectrophotometry: publications by

the staff of the National Bureau of Standards. NBS Letter Circular LC398 (1939).

(63) Colorimetry and spectrophotometry: publications by

the staff of the National Bureau of Standards. NBS Letter Circular LC628 (1939 and 1940).

(64) Colorimetry, spectrophotometry, and photometry:

publications by the staff of the National Bureau

of Standards. NBS Letter Circular LC789 (1941-

1944).

(65) Optical instruments, refractometry and optical properties of glass. NBS Letter Circular LC792 (1945).

(66) The standardization of optical fire-control instru- ments. I. C. Gardner. Army Ordnance 5, 512

(Sept.-Oct. 1924).

(67) Making a standard of planeness. C. A. Skinner. General Electric Rev. 39, No. 8, 528 (August 1926).

(68) Observing an eclipse in Asiatic Russia. I. C. Gardner. National Geographic Magazine 71, 179

(1937).

(69) Corona photography during the eclipses of 1936 and

1937. I. C. Gardner. National Geographic Society, Contributed Technical Papers, Solar Eclipse

Series, No. 1, p. 39 (1939). Ground-and-polished lenses for sun glasses (second ed.) (1940). CS78-40. 5^ Blown, drawn, and dropped lenses for sun glasses (second

ed.) (1940). CS79-40. 5^ Sun glass lenses made of ground and polished plate glass thereafter thermaly curved (1949). CS 159-49. 5(i

(f) Refractometry

(70) Prism refractometry and certain goniometrical re- quirements for precision. L. W. Tilton. BS J. Research 2, 909 (1929) RP64.

(71) Prism size and orientation in minimum-deviation

refractometrv. L. W. Tilton. BS J. Research 6, 59 (1931) RP262.

(72) Permissible curvature of prism surfaces and inac- curacy of collimation in precise minimum-deviation

refractometry. L. W. Tilton, BS J. Research 11, 25 (1933) RP575. 5^. (73) Variations in refractive index of COa-free dry air and

a statistical correlation with solar activitv. L. W.

Tilton. J. Research NBS 13, 111 (1934) RP695. 5L

(74) Refractive index and dispersion of normal and heavy

water. L. W. Tilton and J. K. Taylor. J. Research NBS 13, 207 (1934) RP703. 5?;. (75) Standard conditions for precise prism refractometry.

L. W. Tilton. J. Research NBS 14, 393 (1935)

RP776.

(76) A thin cell for use in determining the refractive indices of crystal grains. C. P. Savior. J. Research NBS 15, 97 (1935) RP814. 5ji. (77) Thermal contiol in minimum-deviation refractometry and temperature coefficients for a medium

flint glass. L. W. Tilton. J. Research NBS 17, 389 (1936) RP919. 5?i. (78) Accurate representation of refractive index of dis- tilled water as a function of wavelength. L. W.

Tilton. J. Research NBS 17, 639(1936) RP934. 5?5. (79) Accurate representation of the refractivity and

density of distilled water as a function of temperature. L. W. Tilton and J. K. Taylor. J. Research NBS 18, 205 (1937) RP971. 5fi. (80) Refractive index and dispersion of distilled water for

visible radiation, at temperatures 0 to 60° C.

L. W. Tilton and J. K. Taylor. J. Research

NBS 20, 419 (1938) RP1085. "l5^. (81) Sources of error in precise commercial refractometrv.

L. W. Tilton. J. Research NBS 30, 311 (1943)

RP1535. 10^.

(82) Measurement of the refractive index and dispersion

of optical glass for control of product. H. L. Gurewitz and L. W. Tilton. J. Research NBS 32, 39 (1944) RP1572. 5^. (83) Refractive index standards of fluorcrown glass. L. W. Tilton. J. Research NBS 34, 599 (1945)

RP1659. 5(5. (84) Sunspot number and the refractivity of drv air. L. W. Tilton. Nature (London) 133, 855 (1933).

(85) Testing and accurate use of Abbe-type refrac- tometers. L. W. Tilton. J. Opt. Soc. Am. 33, No. 7, 371 (1942).

(86) Refractive indices of two thallium bromide-iodide

crystals for visible and infrared radiant energy. Leroy W. Tilton, Earle K. Plyler, and Robert E. Stephens. J. Opt. Soc. Am. (in press).

2. Glass

(a) Methods of Manufacturing Optical Glass

(87) Observations on the formation of seed in optical

glass melts. A. E. Williams. J. Am. Ceram.

Soc. 1, 134 (1918).

(88) Special pots for the melting of optical glass. A. V.

Bleininger. J. Am. Ceram. Soc. 1, 15 (1918).

(89) Optical conditions accompanying the striae which

appear as imperfections in optical glass. A. A. Michelson. Sci. Pap. BS 15, 41 (1919) S333.

(90) Procedures in the manufacture of optical glass. W. S. Williams and C. C. Rand. J. Am. Ceram.

Soc. 2, 422 a919)

17
(91) The equipment of a casting plant for the manufacture of glass pots. F. H. Riddle. J. Am.

Ceram. Soc. 2, 647 (1919).

(92) Notes on the casting of porcelain glass pots. J. W.

Wright and D. H. Fuller. J. Am. Ceram. Soc.

2, 659 (1919).

(93) Optical glass. Heber D. Curtis. Pub. Astronomical

Soc. Pacific 31, No. 180, 77 (1919).

(94) Characteristics of striae in optical glass. T. T. Smith, A. H. Bennett and G. E. Merritt. Sci. Pap. BS 16, 75 (1920) S373.

(95) Notes on porcelain glass pot mixtures. D. H.

Fuller. J. Am. Ceram. Soc. 3, 569 (1920).

(96) Further studies on cast glass pots. R. F. Geller and A. N. Finn. J. Am. Ceram. Soc. 6, 865 (1923).

(97) Making the glass disk for a 70-inch telescope reflector. A. N. Finn. BS J. Research 3, 315 (1929)

RP97; Ind. and Eng. Chem. 21, 744 (1929).

(98) Optical glass at the National Bureau of Standards.

A. N. Finn. J. Opt. Soc. Am. 28, 13 (1938).

(99) Attack on refractory clay pots by optical glasses. Willard H. Parsons and Herbert Insley. J. Research NBS 36, 31 (1946) RP1689. lOfi. (100) Slip casting of clay pots for the manufacture of optical glass at the National Bureau of Standards. Raymond A. Heindl, Gordon B. Massengale, and

Louis G. Gossette. NBS Circular 452, 10^; Glass Industry 27, 177 (1946). (101) Optical glass production. C. H. Hahner. Chem.

Eng. 54 122 (1947). (102) The optical glass industry—past and present. Francis W. Gla7e. Sky and Telescope 6, No. 3, 3-5 and No. 4, 9-11 (1947). (103) Optical glass at the National Bureau of Standards.

F. W. Glaze and C. H. Hahner. NBS Circular 469 (1948); Glass Industry 29;

(b) Effect of Composition on Optical Properties

(104) The density and index of refraction of glass versus

its composition. A. N. Finn and H. G. Thomson.

J. Am. Ceram. Soc. 8, 505 (1925).

(105) The index of refraction of some soda-lime-silica

glasses as a function of the composition. C. A. Faick and A. N. Finn. BS J. Research 6, 993

(1931) RP320; J. Am. Ceram. Soc. 14, 518 (1931).

(106) Index of refraction, density, and thermal expansion

of some soda-alumina-silica glasses as functions of the composition. C. A. Faick, J. C. Young,

D. Hubbard, and A. N. Finn. J. Research NBS

14, 133 (1935) RP762; Glass Industry 16, 81

(1935).

(107) Effect of composition and other factors on the specific refraction and dispersion of glasses. John C. Young and Alfred N. Finn. J. Research NBS

25, 759 (1940) RP1352. 5?i. (108) Changes in the indices of refraction and liquidus of a barium crown glass produced by the partial substitution of some oxides. Edgar H. Hamilton,

Oscar H. Grauer, Zeno Zabawsky, and C. H.

Hahner. J. Research NBS 40, 361 (1948) RP1881, 10^; J. Am. Ceram. Soc. 31, 132 (1948).

(c) Annealing

(109) Concerning the annealing and characteristics of glass. A. Q. Tool and J. Valasek. Sci. Pap. BS 15, 537

(1920) S358.

(110) Annealing of glass. A. Q. Tool and J. Valasek. Pyrometry—a symposium on pyrometry held by

the American Institute of Mining and Metallurgical Engineers, p. 475 (1920). (111) The absorption of heat in glass. A. Q. Tool and

C. G. Eichlin. J. Opt. Soc. Am. 4, 340 (1920).

(112) Certain effects produced bv chilling glass. A. Q.

Tool and C. G. Eichlin.^ J. Opt. Soc. Am. 8, 419 (1924).

,38

.39

14

113) Variations in glass caused by heat treatment. A. Q^: Tool and C. G. Eichlin. J. Am. Ceram. Soc. S' 1 (1925). - in

114) Regarding the heat treatments of glass and its rei fractivitv and density. A. Q. Tool, L. W. Tilton' and E. E. Hill. J. Opt. Soc. Am. & Rev. Scil Instr. 12, No. 5, 490 (1926). 115) The annealing of glass—a nontechnical presentation

A. N. Finn. J. Am. Ceram. Soc. 9, 493 (1926): 116) Cause and removal of certain heterogeneities ii! glass. L. W. Tilton, A. N. Finn, and A. Q. Tool'

Sci. Pap. BS 22, 719 (1927-28) S572.

117) Some effects of carefullv annealing optical glassi L. W. Tilton, A. N. Finn, and A. Q. Tool. J Am. Ceram. Soc. 11, No. 5, 292 (1928). 118) The restoration of solarized ultra-violet transmitting

glasses by heat treatment. A. Q. Tool and R|

Stair. BS J. Research 7, 357 (1931) RP345. m 119) Variations in the optical density of glass. L. W

Tilton. J. Wash. Acad. Sci. 20, No. 1, 12 (1930) 120) The effect of heat treatment on the physical properties of glass. A. Q. Tool and D. B. Lloyd

Fuels and Furnaces 6, 353 (1928). 121) Dimensional changes caused in glass by heatingr

cycles. A. Q. Tool, D. B. Lloyd, and G. E. Meri

ritt. BS J. Research 5, 627 (1930) RP219, lOf

J. Am. Ceram. Soc. 13, 632 (1930). } 122) Variations caused in the heating curves of glass bj, heat treatment. A. Q. Tool and C. G. Eichlin! BS J. Research 6, 523 (1931) RP292; J. Amj

Ceram. Soc. 14, 276 (1931). | 123) Effect of heat treatment on the expansivity of a Pyrex glass. J. B. Saunders and A. Q. ToolJ BS J. Research 11, 799 (1933) RP626. [ 124) Relaxation of stresses in annealing glass. Arthur Q.

Tool. J. Research NBS 34, 199(1945) RP1637. 50. 125) Viscosity and the extraordinar}- heat effects in glass. Arthur Q. Tool. J. Research NBS 37, 73 (1946)' RP1730. lOi. ! 126) Relation between inelastic deformability and thermal expansion of glass in its annealing range. Arthur'i Q. Tool. J. Am. Ceram. Soc. 29, 240 (1946). ' 127) Changes caused in the refractivity and density of glass by annealing. Arthur Q. Tool, Leroy W.,) Tilton, and James B. Saunders. J. Research

NBS 38, 519 (1947) RP1793. 10c.

} d) Measurement of Physical and Optical Properties of Glasses

'

128) Strength tests of plain and protective sheet glass.! T. L. Sorey. J. Am. Ceram. Soc. 1, 801 (1918).; 129) Comparison tests for striae in optical glass by thei Brashear converging light, direct-view method, the! Bureau of Standards tank immersion method and

the short range projection method. L. E. Dodd.i J. Am. Ceram. Soc. 2, 977 (1919). 130) Measurements on the thermal dilatation of glass at high temperatures. C. G. Peters and C. H.

Cragoe. Sci. Pap. BS 16, 449 (1920) S393.

131) The mechanical strength of glazing glass. A. E.

Williams. J. Am. Ceram. Soc. 6, 980 (1923). 132) Measurement of index of refraction of glass at high

temperatures. C. G. Peters. BS Sci. Pap. 20, 635 (1924-26) S521. m.

133) On the constitution and densitv of glass. A. Q. Tool

and E. E. Hill. J. Soc. Glass Tech. (Sheffield, England) 9, 185 (1925). 134) The density of some soda-lime-silica glasses as a

function of the composition. F. W. Glaze, J. C. Young, and A. N. Finn. BS J. Research 9, 799

(1932) RP507.

135) Optical heterogeneitv of a fused quartz disk. L. W.

Tilton and A. Q.'TooI. BS J. Research 3, 619

(1929) RP112. 5(i.

18
138) The viscosity of optical glass. W. H. Wadleigh.

BS J. Research 11, 65 (1933) RP577.

37) Thermal expansions of some soda-lime-silica glasses as functions of the composition. B. C. Schmid,

I A. N. Finn, and J. C. Young. BS J. Research

I 12, 421 (1934) RP667; Glass Industry 15, 48

I (1934).

1 38) Density of some soda-potash-silica glasses as a

function of the composition. John C. Young,

Francis W. Glaze, Conrad A. Faick, and Alfred N. Finn. J. Research NBS 22, 453 (1939)

) RF1197. 50.

:(a39) Improved interferometric procedure with application to expansion measurements. J. B. Saunders.

J. Research NBS 23, 179 (1939) RP1227. 10^. 140) Thermal expansion studies of boric oxide glass and

of crystalline boric oxide. James J. Donoghue

and Donald Hubbard. J. Research NBS 27, 371

(1941) RP1425. 5^.

;141) A precision apparatus for the rapid determination

of indices of refraction and dispersion by immersion. Conrad A. Faick and Bernard Fonoroff.

J. Research NBS 32, 67 (1944) RP1575. 10^. 142) An apparatus for photographing interference phe- nomena. James B. Saunders. J. Research NBS

35, 157 (1945) RP1668. lO^i. 143) Surface tensions of some optical glasses. Leo

Shartsis and Alden W. Smock. J. Research NBS

38, 241 (1947) RP1771, lOfi; J. Am. Ceram. See. 30, 130 (1947).

(,144) Expansion effects shown by some Pyrex glasses. Arthur Q. Tool and James B. Saunders. J. Research NBS 40, 67 (1948) RP1856. 150. 145) Surface tension of compositions in the systems

PbO-BaOa and PbO-SiOa- L. Shartsis, S. Spinner, and A. W. Smock. J. Am. Ceram. Soc. 31, 23 (1948).

(e) Chemical Analysis of Glass

(146) The analysis of soda-hme-glass. G. E. F. Lundell and H. B. Knowles. J. Am. Ceram. Soc. 10, 829 (1927).

i (147) The determination of iron in glass sand. G. E. F. Lundell and H. B. Knowles. J. Am. Ceram. Soc.

11, 119 (1928).

(148) Determination of fluorine and of silica in glasses

and enamels containing fluorine. J. I. Hoffman

and G. E. F. Lundell. BS J. Research 3, 581

(1929) RPllO.

(149) On a modified method for decomposing aluminous

silicates for chemical analvsis. A. N. Finn and

J. F. Klakotka. BS J. Research 4, 809 (1930)

RP180; Ceram. Age 16, 158 (1930).

(150) Determination of magnesium in portland cement and similar materials by the use of 8-hydroxyquinoline. J. C. Redmond and H. A. Bright.

BS J. Research 6, 113 (1931) RP265.

(151) On the direct determination of soda in soda-lime

glasses by precipitation as uranyl zinc sodium

acetate. F. W. Glaze. J. Am. Ceram. Soc. 14,

450 (1931).

(152) Routine determination of boron in glass. F. W.

Glaze and A. N. Finn. J. Research NBS 16, 421

(1936) RP882; Glass Industry 17, 156 (1936).

(153) An improvement in the "partition method" for the determination of boron. Francis W. Glaze and

Alfred N. Finn. J. Research NBS 27, 33 (1941)

RP1401. 50.

(f) Chemical Durability of Glasses

(154) Comparative tests of chemical glassware. P. H. Walker and F. W. Smither. Tech. Pap. 107, 10

(1918) ; Ind. Eng. Chem. 9, 1090 (1917).

(155) Disintegration of soda-lime glasses in water. A. E.

Williams. J. Am. Ceram. Soc. 5, 504 (1922).

156

157

158:

159;

160

161

162

163

164

165

166

167

168

169;

170

171

172;

173

174

175

176

177

The weathering of glass containers. K. L. Ford.

J. Am. Ceram. Soc. 5, 837 (1922). Tests on the resistive qualities of soda-lime glasses to water. L. A. Palmer. J. Am. Ceram. Soc. 6, 579 (1923). Relative solubility of glass in acid solutions as indi- cated bv dye absorption. E. H. Hamilton and

A. N. Finn. Glass Industry 19, 179 (1938). Effect of the solubility of glass on the behavior of the

glass electrode. Donald Hubbard, Edgar H.

Hamilton, and A. N. Finn. J. Research NBS

22, 339 (1939) RP1187. 50. Comparative tests of chemical glassware. Edward

Wichers, A. N. Finn, and W. Stanley Clabaugh.

J. Research NBS 26, 537 (1941) RP1394.

Effect of the chemical durability of glass on the asymmetry potential and reversibility of the glass electrode. Edgar H. Hamilton and Donald

Hubbard. J. Research NBS 27, 27 (1941)

RP1400. 50. Studies of the chemical durability of glass by an

interferometer method. Donald Hubbard and

Edgar H. Hamilton. J. Research NBS 27, 143

(1941) RP1409. 50. Titration and conductivity measurements of aqueous

extracts from bottles. Edgar H. Hamilton and

Donald Hubbard. J. Research NBS 27, 381

(1941) RP1426. 50. Hygroscopicity of optical glasses as an indicator of

serviceability. Donald Hubbard. J. Research

NBS 36, 365 (1946) RP1706. 50. Hygroscopicity and electrode function (pH response)

of glasses as a measure of serviceability. Donald

Hubbard. J. Research NBS 36, 511 (1946)

RP1719. 50. Electrode function (pH response) of potash-silica

glasses. Donald Hubbard. J. Research NBS 37, 223 (1946) RP1743. 100. Voltage anomalies of the glass electrode and the chemical durability of the glass. Donald Hubbard and Gerald F. Rynders. J. Research NBS

39, 561 (1947) RP1848. 100. Effect of annealing and other heat treatments on the pH response of the glass electrode. Donald

Hubbard and Gerald F. Rynders. J. Research

NBS 40, 105 (1948) RP1859. 100.

(g) Transmission of Radiant Energy

Glasses for protecting the eyes from injurious radiations. W. W. Coblentz and W. B. Emerson.

Tech. Pap. 93, 3d ed. (1919). The ultraviolet and visible transmission of eyeprotective glasses. K. S. Gibson and H. J. McNicholas. Tech. Pap. 119, 11 (1919). The ultraviolet and visible transmission of various

colored glasses. K. S. Gibson, E. P. T. Tyndall,

and H. J. McNicholas. Tech. Pap. 148, 13 (1920). Some light-transmissive characteristics of eyeglasses. W. W. Coblentz. Central J. Homeopathy 5, 597 (1924). A nonactinic cobalt blue glass. W.' W. Coblentz

and A. N. Finn. J. Am. Ceram. Soc. 9, 423 (1926). Transmissive properties of eye-protective glass and

other substances. W. W. Coblentz and R. Stair. Tech. Pap. 369, 22, 555 (1928). The transmissive properties of tinted lenses. W. W.

Coblentz. Am. J. Ophthalmology 15, 932 (1932). Spectral-transmissive properties and use of colored

eye-protective glass. W. W. Coblentz and R.

Stair. NBS Circular C421 (1938). Specification of railroad signal colors and glasses. Kasson S. Gibson, Geraldine Walker Haupt, and

Harry J. Keegan. J. Research NBS 36, 1 (1946)

RP1688. 100.

19
(178) Infrared absorption spectra of some experimental

glasses containing rare earth and other oxides. Ralph Stair and Conrad A. Faick. J. Research

NBS 38, 95 (1947) RP1761. 10j5.

(h) Miscellaneous

(179) Variation in soda, lime, and magnesia content of a

glass of the type R03Si02. C. C. Rand. Trans. Am. Ceram. Soc. 17, 236 (1915).

(180) Production of selenium red glass. F. A. Kirkpatrick

and G. G. Roberts. J. Am. Ceram. Soc. 3, 895

(1919).

(181) A study of the origin and cause of stones in glass. H. Insley. J. Am. Ceram. Soc. 6, 706 (1923).

(182) The microscopic identification of stones in glass. H. Insley. J. Am. Ceram. Soc. 7, 14 (1924).

(183) Notes on the behavior of refractories in glass melting

furnaces. H. Insley. J. Am. Ceram. Soc. 7, 583

(1924).

(184) The failure of thermocouple protection tubes in glass

melting furnaces. H. Inslev. J. Am. Ceram. Soc.

8, 605 (1925). (185) Tank control and devitrification. H. Insley. Glass Industry 7, 1 (1926).

(186) Some observations of surface deposits formed in glass furnace regenerators. H. Insley. J. Am. Ceram.

Soc. 9, 635 (1926).

(187) The petrographic microscope as an instrument for the* glass technologist. H. Insley. J. Am.

Ceram. Soc. 11, 812 (1928). (188) Determination of the source and the means of pre- vention of stones in glass. H. Insley. BS J. Research 2, 1077 (1929) RP71, 5^; J. Am. Ceram.

Soc. 12, 143 (1929).

(189) The service of refractory blocks in a small experimental glass tank". W. L. Pendergast and H.

Insley. BS J. Research 2, 453 (1929) RP44.

(190) Defects produced by stones in glass. H. Inslev. Glass Industry 16, 79 (1935).

(191) Gases in some optical and other glasses. Clarence Hahner, George Q. Voigt, and Alfred N. Finn.

J. Research NBS 19, 95 (1937) RP1014. 50. (192) Observations on crystalline silica in certain devitrified glasses. A. Q. Tool and H. Insley. J. Research NBS 21, 743 (1938) RP1152. 10(5. (193) Potash in the glass industry. A. N. Finn. Ind. Eng. Chem. 30, 891 (1938).

(194) Publications on glass technology and a list of standard samples of interest to the glass industr^• NBS Letter Circular LC841 (1946).

(195) An improved method for detecting casehardened

glass as a mirror component. J. J. Diamond.

Glass Industry 26, 372 (1945). Washington, March 1, 1949.

o

20