Great Moments in Packaging: No 4 – Spring Scales
You might think that the advent of computers and microchip technology had rendered the good old spring scale redundant, but direct descendants of the device first invented about 250 years ago are still very much in common use. And while modern day industrial weighing scales may not actually use springs, they do still work on exactly the same principle.
Weight measurement devices – in the form of balance scales – have been around for millennia; evidence includes marked and proportionately weighted stones from ancient Egypt and Pakistan, possibly from as far back as 2400BC. You can even see one in an illustration in the Egyptian Book of the Dead!
Fast forward a few thousand years…
In the late 1760s, a man named William Salter was making pocket steelyards in Bilston, Staffordshire. A pocket steelyard is a straight-beam balance with arms of unequal length, incorporating a counterweight which slides along the calibrated longer arm to counterbalance the load and indicate its weight. His brother Richard, a buckle maker, fashioned a spring out of an old file, added it to the device and thus was born the spring scale.
By 1838, the company set up to make and sell Salter scales had moved to West Bromwich and was known as George Salter & Co. In that year George obtained a patent for a “‘spring balance or spring weighing apparatus, with a method of indicating the weights by means of an index and scale of divisions marked on the exterior of a tube either curved or plane sided”. Now you may not realise it, but that pretty much describes many kitchen, bathroom and postal scales still used today; what it basically says is that when you place an item on a tray or a hook to be weighed, the stretching (or compression) of a spring causes a pointer on a dial to show the weight! (For those of you who have only vague memories of your GCSE physics, it’s all based on Hooke’s Law, which states that the extension of a spring is in direct proportion with the load applied to it.)
Spring scales, 21st-century style
As mentioned earlier, many of today’s digital domestic and weighing scales still use the same strain-gauge principle as that devised by Richard Salter in the 1760s. Instead of using springs, however, an electronic load cell measures a change in electrical resistance when an item is placed on a platform, allowing a calculation of the item’s weight.
The Salter company continued to grow and innovate, making not just scales but also irons, mincers, potato chippers, coin-operated machines and, another first for the UK, the typewriter. By the 1950s, Salters were still owned by the same family and were employing over 2000 people in their West Bromwich base. On the way, they had also, incidentally, set up the football club that would become West Bromwich Albion, formed by workers of the factory in 1879; when Albion played in the FA Cup final in 1886, seven Salter employees were in the team!
All this from one moment of inspiration on the part of a West Midlands buckle maker!
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