The rapid development of electronics and computerization in the mid 20th century, and the invention of the digital scales, crowded out, almost entirely the use of mechanical scales.
Because of this, the mechanical scales became collectors' items. Most mechanical scales are works of art, and are hand crafted. The work is precise and gives an authentic feel of the era in which they were created.
The Structure and Sensitivity of Scales
Mechanical scales have a few basic parts and many supplements that depend on the specific use of the scale.
The main part of an Equal Arm Beam Balance is the beam. The pans are connected to the beam-ends usually with an axis. At the center of the beam is the fulcrum or pivoting point, from which the scales were connected to a stand or hung. To produce a good balance the position of the pivoting point in the beam is an important problem, as is the attachment of the beam to a stand. At the center, there is also a pointer, which indicates whether the scale is balanced.
The sensitivity of the scales depends on 3 main factors: a) the amount of friction in the different hinges. The less friction there is, the more sensitive the scale. B) The total mass of the different parts of the scale. C) The length of the main beam.
Different Types of Mechanical Scales
Equal Arm Beam Balance
This type of scale has been used since ancient times. These scales have two concave pans hanging from a beam. The beam is hanging from a hinge that allows for vertical movement of the beam. The actual weighing is done by placing weights of known value on one pan, so that the other pan, which holds the goods, will be evenly balanced. Most scales were of this type but they varied in length, from 5 cm (2 inches) to 3 meters (about 3 yards). These types of scales were not precise because of the high friction in the hinges.
In order to lessen the friction a mathematician called M. Gilles de Roberval invented in 1730 scales with a double main beam that had two hinges. In that way, the stress lessened on the main hinge by half, and the precision grew immensely. Manufacturing Roberval scales with the pans above the beam started only at the beginning of the 19th century. This development allowed the scales to be placed on a table or shelf and therefore simplify the weighing process. These types of scales caught on very fast and .
Unequal Arm Steelyard Balances
These scales work on a lever principle. They have unequal beam arms. A pan is suspended from the short arm. One movable weight is attached to the longer arm. At the place where equilibrium is achieved, the weight of the object on the pan is indicated on an engraved scale. The advantage of this type of scale is that only one weight is used for a wide range of loads.
The steelyard was very common in medical clinics for weighing humans, in warehouses for weighing large loads, and also in large bridge scales for weighing trucks and trains.
Another type of these scales are the Bismar scales which have a fixed pan and a fixed weight but the movement is in the central axis which can be moved along the beam.
Spring Scales
In 1698, Christof Weigel of Germany described a new kind of scale, which has no pans or weights, but uses a spring.
The weight of an object is determined by monitoring the deformation in an elastic material (usually a metal spring) caused by the object that is being weighed. The degree of deformation is indicated by a pointer on a scale, which is part of the instrument.
The most common spring scale is a cylinder in to which a spring is inserted. The spring can be pulled by hanging the load beneath it or compressed by putting the load on top of it. The change in the spring length is used to estimate the weight.
Pendulum Scales
These scales are small. They have a lever arm on which the load is put, and a longer arm, shaped like a pendulum, with a weight on its end. When pressing the lever arm (adding a load) the pendulum arm swings up. An indicator on the central axis shows the anomaly. The numerical value of this anomaly is the weight of the load.
The Different Uses of Scales
Table Scales
These scales are of different types (equal arm, spring etc.). They were used in markets at the grocer's or the butcher's. Simple table scales were built so that the load and weights can be placed on pans. The pans were usually placed above a central beam or with two beams in the Roberval principle. The scales were often inside a wooden box or on a decorated steel frame. Small table scales are very collectible where as large ones have no real collectible value.
Some table scales have a dial, which indicates the weight; these usually have one pan and work on a spring being compressed by the weight of the load.
Chinese "Opium" Scales
These scales have one pan suspended from an unequal ivory arm, and a brass weight for counterbalance. A load is put on the pan and then the weight is moved a long the arm until the scale is balanced. These scales are usually found inside a wooden box, with the distinctive shape of a fish or violin. These scales originated in China and were first mentioned in western literature in the 17th century, as Dotchin scales. They were used to weigh silver, gold, gems, and medicinal powders.
Coin Verification Scales
Verifying the correct weight of gold and silver coins is an age old practice. The weighing was done on very precise scales, but until the beginning of the 18th century, it was possible to verify one ounce with maximum precision of only 0.1 grams. With an aim at improving the accuracy and sensitivity of the scales, their mass was lightened and the hinges were improved. Many new small scales were invented.
In 1770, pocket scales were introduced. The scales were inside a box. Inside the box were small equal arm scales for weighing a small coin.
In 1817 with the introduction of the gold Sovereign the rocker balance was invented. These scales were balanced only if the weight of the coin was exact. It was also possible to verify the diameter and the thickness of a coin using these same scales. As of 1860, the minting of coins was much improved so that forging was nearly impossible. After a while, the merchants stopped using these types of scales, and shortly after, their production stopped completely.
Postal Scales
The most popular scales among collectors are postal scales.
As of 1840, the practice of adding stamps to letters and packages was established. The amount of payment due was based on the weight of the letter.
Nearly all types of scales were used as postal scales: Scales with the pans hanging bellow the central beam, scales with the pans placed above the central beam, spring scales where the spring is stretched, spring scales where the spring is compressed, pendulum scales and more.
Kitchen Scales
These scales were used mainly for measuring quantities of ingredients used for precise cooking. They were usually table spring- scales. The range that these scales could weigh was usually small. Special attention was given to their design, which were used as a decorative item as well as a functional one.
Apothecary or Analytical Scales
Scales that were very precise and sensitive first came into use only in the 18th century. These equal arm scales were used by doctors, pharmacists, and chemists that made their own medicines and concoctions. Analytical scales are characterized by their delicate central beam and small pans, usually made of glass or brass. In order to attain maximum accuracy, great pains were taken to lessen the friction of the hinges, so the hinges were built on very sharp steel edges. Usually one finds these scales built into a box, which incorporates a level and screws for fine-tuning. Very often, the scales are enclosed in a glass cover.
Textile and Paper Scales
Different textiles and paper very in their weight per square unit. So in the beginning of the 19th century special scales were invented. The results they gave were not in units of weight but in weight pertaining to area (ounce to square inch)
Merchants dealing in paper or textile used to carry these scales with them to determine the quality and standard of the wares.
Grain Scales
In every flourmill and grain silo, there are special scales (Chondrometer) for weighing the grain. The weight of the grain is one of the more important factors in its quality. The scales were equal arm balances, but instead of pans there were copper cylinders of a known weight and volume. When the cylinders were filled with grain, the resulting weight was in weight pertaining to volume (pound to gallon).
Egg Scales
Most egg scales were spring scales. The earlier models, in which each egg was weighed separately, were based on a springy metal strap with a spoon like depression on top. Later scales were built that could weigh simultaneously a large number of eggs and sort them accordingly. There were a great many designs and methods of construction and, although they were of little aesthetic merit, their technical quaintness gave them great charm.
Epilogue
The bible mentions numerous accounts of weighing. In Genesis chapter 23, Abraham wishes to purchase from Ephron the Hittite a burial cave called Machpelah (vs. 8-19), so that he can bury his wife Sarah.
Ephron says to Abraham: "The land is worth four hundred silver Shekels, but what can this be between me and thee?" "…And Abraham weighed to Ephron the silver…" "So the field of Ephron… were made sure unto Abraham for a possession…"
This is the first purchase of commodities that is mentioned in the Bible, which uses weighing.
Bibliography
1) Kisch Bruno, Scales and Weights
Yale Studies in the History of Science and medicine. Yale Univ. Press. 1965
2) Turner Gerald, Scientific Instruments 1500-1900
University of California Press. 1998
3) Mechira Pumbit Magazine Vol. 20 2000.
This type of scale has been used since ancient times. These scales have two concave pans hanging from a beam. The beam is hanging from a hinge that allows for vertical movement of the beam. The actual weighing is done by placing weights of known value on one pan, so that the other pan, which holds the goods, will be evenly balanced. Most scales were of this type but they varied in length, from 5 cm (2 inches) to 3 meters (about 3 yards). These types of scales were not precise because of the high friction in the hinges.
In order to lessen the friction a mathematician called M. Gilles de Roberval invented in 1730 scales with a double main beam that had two hinges. In that way, the stress lessened on the main hinge by half, and the precision grew immensely. Manufacturing Roberval scales with the pans above the beam started only at the beginning of the 19th century. This development allowed the scales to be placed on a table or shelf and therefore simplify the weighing process. These types of scales caught on very fast and .
These scales work on a lever principle. They have unequal beam arms. A pan is suspended from the short arm. One movable weight is attached to the longer arm. At the place where equilibrium is achieved, the weight of the object on the pan is indicated on an engraved scale. The advantage of this type of scale is that only one weight is used for a wide range of loads.
The steelyard was very common in medical clinics for weighing humans, in warehouses for weighing large loads, and also in large bridge scales for weighing trucks and trains.
Another type of these scales are the Bismar scales which have a fixed pan and a fixed weight but the movement is in the central axis which can be moved along the beam.
In 1698, Christof Weigel of Germany described a new kind of scale, which has no pans or weights, but uses a spring.
The weight of an object is determined by monitoring the deformation in an elastic material (usually a metal spring) caused by the object that is being weighed. The degree of deformation is indicated by a pointer on a scale, which is part of the instrument.
The most common spring scale is a cylinder in to which a spring is inserted. The spring can be pulled by hanging the load beneath it or compressed by putting the load on top of it. The change in the spring length is used to estimate the weight.
These scales are small. They have a lever arm on which the load is put, and a longer arm, shaped like a pendulum, with a weight on its end. When pressing the lever arm (adding a load) the pendulum arm swings up. An indicator on the central axis shows the anomaly. The numerical value of this anomaly is the weight of the load.
These scales have one pan suspended from an unequal ivory arm, and a brass weight for counterbalance. A load is put on the pan and then the weight is moved a long the arm until the scale is balanced. These scales are usually found inside a wooden box, with the distinctive shape of a fish or violin. These scales originated in China and were first mentioned in western literature in the 17th century, as Dotchin scales. They were used to weigh silver, gold, gems, and medicinal powders.
Verifying the correct weight of gold and silver coins is an age old practice. The weighing was done on very precise scales, but until the beginning of the 18th century, it was possible to verify one ounce with maximum precision of only 0.1 grams. With an aim at improving the accuracy and sensitivity of the scales, their mass was lightened and the hinges were improved. Many new small scales were invented.
In 1770, pocket scales were introduced. The scales were inside a box. Inside the box were small equal arm scales for weighing a small coin.
In 1817 with the introduction of the gold Sovereign the rocker balance was invented. These scales were balanced only if the weight of the coin was exact. It was also possible to verify the diameter and the thickness of a coin using these same scales. As of 1860, the minting of coins was much improved so that forging was nearly impossible. After a while, the merchants stopped using these types of scales, and shortly after, their production stopped completely.
The most popular scales among collectors are postal scales.
As of 1840, the practice of adding stamps to letters and packages was established. The amount of payment due was based on the weight of the letter.
Nearly all types of scales were used as postal scales: Scales with the pans hanging bellow the central beam, scales with the pans placed above the central beam, spring scales where the spring is stretched, spring scales where the spring is compressed, pendulum scales and more.
Scales that were very precise and sensitive first came into use only in the 18th century. These equal arm scales were used by doctors, pharmacists, and chemists that made their own medicines and concoctions. Analytical scales are characterized by their delicate central beam and small pans, usually made of glass or brass. In order to attain maximum accuracy, great pains were taken to lessen the friction of the hinges, so the hinges were built on very sharp steel edges. Usually one finds these scales built into a box, which incorporates a level and screws for fine-tuning. Very often, the scales are enclosed in a glass cover.
Different textiles and paper very in their weight per square unit. So in the beginning of the 19th century special scales were invented. The results they gave were not in units of weight but in weight pertaining to area (ounce to square inch)
Merchants dealing in paper or textile used to carry these scales with them to determine the quality and standard of the wares.
