Transcriber’s Notes:
Equal signs “=” before and after a word or phrase indicate =bold=
in the original text.
Small capitals have been converted to SOLID capitals.
Illustrations have been moved so they do not break up paragraphs.
Old or antiquated spellings have been preserved.
Typographical errors have been silently corrected.
SELENIUM CELLS
THE CONSTRUCTION, CARE AND USE
OF SELENIUM CELLS WITH SPECIAL
REFERENCE TO THE FRITTS CELL
BY
THOS. W. BENSON
NEW YORK
SPON & CHAMBERLAIN, 120 LIBERTY STREET
LONDON
E. & F. N. SPON, LIMITED, 57 HAYMARKET, S. W.
1919
Copyright, 1919
BY THOMAS W. BENSON
VAIL-BALLOU COMPANY
BINGHAMTON AND NEW YORK
APPRECIATIVELY
DEDICATED
TO
J. A. STELTZER
FOREWORD
The lack of definite information relative to the construction of
selenium cells has led the writer to put in this form the results of
some of his experiments. The method described was originated by Mr. C.
E. Fritts but the apparatus used was developed by the writer.
Despite the fact that sensitive cells are very difficult to construct
by the methods in vogue the use of apparatus described practically
eliminates failures, the cells, almost without exception, being useful
for one purpose or another.
This is by no means the last word on the subject. Many improvements
are possible and have been pointed out in the text. Should these
instructions but serve to interest others in the fascinating study they
will have served their purpose.
THOS. W. BENSON.
Philadelphia, Pa.
CONTENTS
PAGE
CHAPTER I
SELENIUM, THE ELEMENT 1
Discovery, Naming and Classification. Where Found
and Method of Extraction. Three Forms, Amorphous,
Vitreous and Metallic.
CHAPTER II
CONSIDERATION OF CELL TYPES AND THEIR CHARACTERISTICS 5
Factors in Design. Bildwell Cell. Application of
Selenium and Annealing. Ruhmer Cell. Bell and
Taintor Cell. Mercadier Cell. Gripenberg Cell.
Theory of Operation.
CHAPTER III
THE CONSTRUCTION OF FRITTS SELENIUM CELL 20
Description of Hot Press. Accessories for Press.
Other Apparatus Required and Supplies. Preparing
Copper Plate. Applying Selenium. Treating in Hot
Press. Application of Gold Foil. Assembling Cell.
CHAPTER IV
TESTING AND MATURING SELENIUM CELLS 32
Two States. Testing and Maturing Set. Accessories
for Set. Construction of Rheostat Arm for Wheatstone
Bridge. Measurement of Cells by Bridge
Method. Tests for Light Sensitiveness. Proper
Voltage. Classification of Cells. Testing for
Polarization. Treating with A. C. Raising Resistance
of Cells. Testing for Current Generation. Reconstruction
of Useless Cells. Measurement of Cells by
Substitution Method. Sealing Cells.
CHAPTER V
APPLICATIONS OF SELENIUM CELLS 51
Photometric Applications. Transmission of Speech
Over Beams of Light. Automatic Control of Light
Buoys and Isolated Lights. As Recorder of Sunlight.
Astronomical Applications. Talking Pictures.
The Phonoptican, How the Blind May Read by
Sound. Controlling Mechanisms at a Distance.
Electric Dog. Use in Cable Telegraphy. Burglar
Alarm. Selenium Batteries, Current Generators.
Telephonic Properties. Effect of Different Current
Sources on Sensitiveness of Cells.
CHAPTER VI
THE CARE OF SELENIUM CELLS 62
LIST OF ILLUSTRATIONS
FIG. PAGE
1. Bildwell Cell 7
2. Ruhmer Cell 10
3. Bell and Taintor Cell 12
4. Mercadier Cell 14
5. Gripenberg Cell 15
6. Fritts Cell 17
7. Hot Press with Cell in Place 21
8. Details of Hot Press (elevation) 22
8. Details of Hot Press (plan) 22
9. Platen for Cell; and Template for Applying Selenium 24
10. Fiber Pieces for Enclosing Cell 26
11. Mode of Assembling Cell 30
12. Testing and Maturing Set 33
13. Layout and Wiring Diagram of Testing Maturing Set 35
14. Connections for Buzzer and Induction Coil to Produce
Alternating Current 36
15. Connections for Interior of Rheostat Box 38
16. Circuit for Wheatstone Bridge Measurement 40
17. Circuit for substitution Method of Measurement 47
18. Showing Cell ready for Assembly with Four Complete
Cells in background 49
CHAPTER I
SELENIUM, THE ELEMENT
Over a century ago, 1817 to be exact, the Swedish scientist Berzelius
discovered a new element in the lead chambers used for the manufacture
of sulphuric acid by roasting iron pyrites. Noting its resemblance
to Tellurium, the name for which having been derived from the Greek
for Earth, Tellus, he named the new element Selenium derived from
the Greek for Moon, Selene. The ending ’um being used to indicate a
metal according to the practice of naming newly discovered elements.
Although believed to be a metal for many years, the chemical reaction
of Selenium resembles that of sulphur to such a degree that it is now
accepted to be a non-metal in its amorphous and vitreous forms. In its
third or crystalline state it has many metallic characteristics and in
this form termed metallic selenium. In the Periodic System it occupies
the place between Tellurium and Sulphur.
Designated by the symbol Se, selenium has been found in all parts of
the globe in small quantities, chiefly in combination with copper, lead
and silver forming selenides, in certain pyrites and occasionally in
its pure state. It was found in meteoric iron by Warren in 1909.
An idea of its wide distribution may be gained from the following table:
Mineral Composition Location
Sulphur Selenide in natural sulphur Lispau Islands
Eucarite Selenide of silver and copper Chili
Crooksite Selenide of silver, copper and thallium Norway and
Sweden
Clauthalite Selenide of lead Germany
Lehrbachite Selenide of lead, copper and mercury Germany
Zorgite Selenide of lead and copper Germany
The element is obtained commercially as a by-product from the
manufacture of sulphuric acid, various methods of extracting it from
the chamber mud being employed. The usual process is to heat the well
washed chamber mud with potassium cyanide and nitrate to obtain an
alkaline selenate. The element is then precipitated with hydrochloric
acid or sulphur dioxide.
=Selenium= exists in three well defined forms, Amorphous, Vitreous and
Metallic.
=Amorphous Selenium.= This form is obtained as a finely divided brick
red precipitate when sulphur dioxide is passed thru selenic acid. It is
soluble in sulphuric acid and slightly so in carbon disulphide. It has
a Sp. Gr. of 4.26, with no definite melting point, softening gradually
and running together between 80° and 100° C. In this state it is an
insulator.
=Vitreous Selenium.= When the amorphous selenium is heated to 217° C
and rapidly cooled the vitreous form results. It is now a red vitreous
mass, slightly less soluble in carbon bisulphide. When a thin film is
held up to the light it shows blood red in color. Sp. Gr. 4.28, Atomic
Weight 79.5. This form is practically an insulator having a resistance
of 6 × 10⁹ ohms per Cu. Cent. at 75° C or about 3.8 × 10¹⁰ as great as
that of copper. It can be electrified by friction. Vitreous selenium
has no definite melting point being hard and brittle at 40° C and
softening gradually as the temperature rises, becoming fluid at 210° C.
=Metallic Selenium.= By cooling melted vitreous selenium to 210° C
and holding it at that temperature for a short time the metallic
form results. The element is now a black glossy opaque mass, a fair
conductor of electricity but improving greatly under the influence of
light. It melts between 217° and 220° C, Sp. Gr. 4.788, insoluble in
carbon disulphide but will dissolve in sulphuric acid to form a green
solution. It is the latter form that is used in the construction of
selenium cells.
When selenium is vaporized by heat it gives off dark brown fumes having
an odor similar to rotting cabbage. These fumes are poisonous and care
should be taken that they are not breathed to excess.