This might be a convenient moment to describe the heater tester used for all cigarettes and tobacco tins not put through the Thermokept or Tingey cold vacuumising machines.*
These testers were large cylinders 7' long x 3' diameter, fitted with 23 tubes each 3½" diameter which were surrounded with steam heater coils. The cylinder rotated slowly on its axis, making one revolution every 40 seconds. Steam was applied to the coils at 30-35 lbs in² which produced a temperature inside the tubes of about 280°F.
Tins were placed into the tubes as the cylinder rotated pushing preceding tins through the tubes until they fell out down a chute at the other end. At the exit end, the thin tagger plate which had become distended by the heat in the tester was "pricked" with a gramophone needle held in a stick of solder. The heated air inside the tin pushed out and the puncture was immediately soldered. The application of the hot iron burned up most of the air remaining in the tin, leaving a partial vacuum of around 4½ inches.
The time taken for a tin of cigarettes to pass through the heater was about 6½ minutes.
For tobaccos, however, the heating feature of the testers was in effect used to extend the processing of the tobacco.
The number of tins fed into each tube and the number of tubes used was varied according to a very carefully calculated formula for each and every brand and packing so that some passed through the heater in 9 minutes whereas others took 22½ minutes.
Some brands, especially the darker flakes or navy cuts were put through a second time after a 48 hour interval so that the total time in the heater was often as much as 50 minutes.
This treatment of tobaccos had been practised since the earliest days and was considered to be an essential part of the processing.It was only abandoned when tobacco packings changed to snap vac or skruseal packings some time after World War 2.
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*note: the 2 machines mentioned above made slightly cheaper to produce tins and were less labor intensive, but resulted in a lower vacuum of 2-3", while the conventional heat processed cutter-top usually had 4-5", but all tins still had to be checked after the sealed fact for "leakers".