Too Good to Burn or SPEAKING THROUGH COAL

Series

Series Name

Mining Review 13th Year

Issue

Issue No.

4

Date Released

Dec 1959

Stories in this Issue:

1. 1THE ART OF MINING
2. 2MOUNTED MINORS
3. 3Too Good to Burn or SPEAKING THROUGH COAL
4. 4RECORD PIT

Story

Story No. within this Issue

3 / 4

Summary

NoS synopsis: a look at Welsh anthracite and its use as one of the most important materials in telephones (carbon granules)
NCB Commentary - From the anthracite pits of Wales comes the most important ingredient of a modern telephone. It’s anthracite - it must be special because it can cost about £50 per ton. Picked from selected seams, it’s taken to Area Laboratories where every separate piece is inspected by hand. Only very small quantities are required but they make a lot of telephones. It must be clean, hard and bright without streaks of mineral matter; its carbon content must be exceptionally high; it must have very little sulphur. These are the requirements of the men who make telephones - requirements which are met before the coal is sent away.
Every ‘phone call you make depends on the carbon in the mouth piece and purest carbon comes from anthracite. At the factory it’s processed still further - the lumps are broken to a fine powder. Time and time again it is ground until the required size is reached. The telephone transmitter depends on the unique property of carbon granules. Their electrical resistance varies according to the pressure placed on them - even such minute pressures as the voice can give.
In this way sound waves are changed into electrical impulses. Baking is an important part of the process; and after-magnets remove iron impurities.
Meanwhile, the telephones are being assembled with a dexterity which no doubt surprises the do-it-yourself-home-handyman.
The outsides - the cases - are moulded in diakon plastic at a pressure of 1,000 lbs. a square inch. The process is almost entirely automatic.
Now our carbon is added - a special instrument placing the exact quantity into the transmitter shell.
On goes the mouth piece and the new-type C. P. O. phone is nearly finished and, lets face it, it’s all possible because of anthracite.

Researcher Comments

Commentary recorded 9th November 1959.

Keywords

Industry and manufacture; Mining

Written sources

British Film Institute Databases   Used for synopsis
Film User   Vol.14 No.167 September 1960, p520.
The National Archives COAL 32   /12 Scripts for Mining Review, 1956-1960

Credits:

Production Co.

Documentary Technicians Alliance

Sponsor

National Coal Board