Chapter I: 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.