Balance is a commonly used instrument in laboratory. Balance is a weighing instrument, and it is also an instrument for measuring the mass of objects. It is made according to the lever principle. There are two small plates at both ends of the lever, one for putting heavy objects and the other for weighing objects. The center of the lever is equipped with a pointer. When the two ends are balanced, the masses (weights) of the two ends are equal. These truths are commonplace for people who have studied physics. Modern scales are more and more accurate, more sensitive and more and more kinds. As we all know, there are ordinary balance, analytical balance, constant analytical balance, micro analytical balance, semi-micro analytical balance and so on. It should be noted that the balance did not suddenly develop into what it is today, but it still has a history of development!

The invention of the balance was very early. In the Nile Delta of Egypt, there is an aquatic plant, which is very similar to the reed growing in our waters. Its stems are peeled off layer by layer and torn into thin slices for writing. This thing is called papyrus. Paper in many European countries evolved from Latin papyrus. Books written with papyrus are papyrus, which became an important historical document in ancient Egypt. What we know about ancient Egypt now, especially the historical development of science and technology, comes from the records in papyrus. Of course, the cursive characters on paper are not modern characters, but hieroglyphics, which many experts have seen. According to the papyrus, as early as 1500 BC, the Egyptians had already used scales. Others say that the Egyptians used scales even earlier, about 5000 BC. Although the ancient Egyptian balance was very rough, it already had the outline of modern balance and became the embryonic form of modern balance. The picture below shows the scales used by the ancient Egyptians.

As can be seen from the picture, this balance is to drill a hole in the middle of a vertical stick, cross a stick and hang a plate at both ends of the stick with a rope. This kind of balance was used for a long time until about 500 BC, when the Roman "rod weight" appeared. By moving the weight, the weight of the rod keeps balance with the weight of the weighed object. In fact, it changes one end (weight end) of the balance from fixed to movable. Its advantage is that only one weight is needed, and the balance weight is better. The steelyard also hangs a plate with a rope and then hangs a weight with a rope. The basic form is the same as that of a balance except that one end can be moved.

In the use of scales and scales, people find it troublesome to hang plates with ropes and inconvenient to use. So, some people want to get rid of this nasty rope. /kloc-In the middle of the 7th century, the French mathematician Lauber Barr invented the swinging tray balance. The invention of pallet balance is considered as a great improvement on the ancient hanging balance, and it is still widely used today. The following picture shows a common pallet scale in the laboratory now, which is greatly improved compared with the pallet scale in17th century. 1 in the figure is a balance beam, and both ends support the weighing plate 2. These two parts constitute the skeleton of the pallet scale and embody the basic design principles of the pallet scale. See the following schematic diagram: when the beam 1 is balanced, the moments are equal, F 1L 1=F2L2, F 1 = M 1g, F2=m2g, L 1 =. In the figure below, 3 is the pointer, 4 is the dial, and the pointer is aligned with the center of the dial to indicate the balance at both ends, 5 is the code walking ruler, 6 is the code walking, and 7 is the zero adjusting nut. There are also weights that match the balance.

It should be pointed out that the invention of pallet scale did not make the hanging scale withdraw from the historical stage. On the contrary, the hanging balance not only continues to be used by people, especially scientists, but also continues to be improved in use. The precision balance widely used in modern times is mostly suspended, while the pallet balance is more used in daily production and life, and more used in weighing with low precision requirements in scientific experiments.

British chemist Blake used the balance earlier in chemical experiments. He lived and worked in the18th century. At that time, gas was constantly discovered in chemistry and the theory began to be established. Blake attached great importance to experiments in chemical research and was the first person to study gases by quantitative methods. 1755 wrote a paper on the experimental study of alkaline substances such as limestone. The paper mentioned that he found that burning limestone would produce gas. So, he weighed the limestone before calcination and once again after calcination. It was found that the weight of limestone was reduced by 44% after calcination, which he thought was the weight of gas released from it. On this basis, he conducted various studies. For example, he reacted limestone with acid and found that gas was also produced. He absorbed the gas with limewater and made a quantitative study. He found that the weight of this gas is equal to the weight of the gas produced by calcining limestone, from which he realized that there is a gas in limestone that is fixed, which he called "fixed air" (that is, carbon dioxide as we know it now). From Blake's experimental research, we can know that he is conducting quantitative research, which requires weighing, and weighing cannot be separated from scales. Historical data show that Blake did use the balance, and the balance he used is still preserved in the Royal Museum of Edinburgh. The picture below shows the balance used by Blake.

The scale is hung with a rope, and the beam is hung on another scale hook. It was with this balance that Blake made a discovery in the chemical experiment. The use of this balance not only establishes the quantitative method in chemical experiments, but also has great significance for the further development and improvement of this balance.

After Blake, the British chemist Henry cavendish also carried out accurate quantitative experiments, and it is said that he also designed and manufactured the balance. Because cavendish's life information is unknown, it is difficult to know exactly when and how he designed and manufactured this kind of balance. Later, the balance used by cavendish was exhibited in the Royal Academy of Sciences. This balance is placed in the cupboard, and the style of the balance can't be seen clearly from the outside, as shown in the following figure:

As we know, lavoisier, a famous French chemist, attaches great importance to quantitative research. He often uses the balance and pays attention to the accuracy of weighing. It was in the precise quantitative research that lavoisier determined the existence of oxygen and established the scientific theory of oxidative combustion. When using quantitative methods to study chemical changes, it is necessary to assume that the mass of substances is conserved before and after chemical changes, and lavoisier established the law of mass conservation. Lavoisier's research work was helped by the balance, but lavoisier himself rarely designed and manufactured instruments, nor did he design and manufacture the balance. However,/kloc-scales popular in France in the 0/8th century are sold in many small shops. Lavoisier may benefit from this favorable condition. What we see in the picture below is the style of18th century French balance, perhaps a style of balance at that time.

/kloc-at the end of 0/8, Britain also made a balance by embedding a steel blade in the center of the beam. Putting it in an agate plate greatly improves the precision and sensitivity. At this time, some balance designers and manufacturers appeared. However, it is said that the balance is more expensive and must be booked in advance. Unlike France, scales are not so accurate, but they are relatively easy to buy. The picture below shows the balance made by Federer for the Royal Society, which is on display at the Science Museum in London.

In Britain, the use of scales is not limited to chemists and scientists, but also widely used in general pharmacies. Dalton, the proponent of chemical atomism, often uses scales in scientific research. Dalton became a famous figure and chemist because of his important position in the history of chemistry and his influence in the British scientific community. The balance he used is said to have become something extraordinary, and it was later owned and collected by the Manchester Society of Literature and Philosophy. Dalton used to be a member of this society.

In the 1920s, there was a musical instrument designer named Robinson in London. He began to design and manufacture analytical balances, which were used not only in Britain but also in the United States. Robinson made beams and triangles out of hollow materials, with a pointer in the middle of the vertical beam.

The balance with scale beam and travel code was also born around19th century (the pallet was introduced earlier, and the scale and travel code are marked on the beam in the figure). Who is the inventor of this kind of balance? There are different opinions and disputes. However, in 185 1, an international exposition was held in London, and some major balance manufacturers from Britain and continental Europe participated in the exposition. After deliberation by the judging panel of the World Expo, the highest award was finally awarded to Ling in recognition of his contribution in manufacturing scales with graduated beams and sliding devices (that is, mobile codes). As a result, Ling's right of invention and creation has been confirmed internationally.

For a long time, there is a popular theory in the balance manufacturing industry, that is, the longer the beam of the balance, the more sensitive the balance is. But there is a man named Bohr Bonger who is not limited by this theory. 1866, he designed and manufactured the short beam analytical balance. Later, he also made achievements in Hirata's design theory. The picture below shows the earliest short scale made by Bonger in 1866.

The improvement of balance is not only in light beam, contact point, wandering code, scale, etc., but also in other aspects. For example, the knob balance,1appeared in the first half of the 9th century. What are the advantages of knob balance? In the early balance, the beam was installed on the column, and it was the same whether it was used or not. Later, analytical balance appeared, and the blade of analytical balance was made of agate. In order to reduce the damage of the blade, the beam of the balance is placed on a shelf when it is uneven, so that the blade is no longer stressed, and the blade is placed on a supporting bowl when it is used. These are all controlled by the knob device. Modern analytical balance has a knob device. The figure below shows the knob balance made by 1833.

With the development of science and technology, the design and manufacture of balance have made great progress. It is through the unremitting efforts of several generations and the accumulation and perfection of technology that all kinds of modern scales have come into being today. Now in the chemistry laboratory, the commonly used balances are: the tray balance, mentioned earlier, is used to measure the approximate mass of substances with low accuracy requirements, and can weigh100g, 200g, 500g or even100g; Analytical balance (constant analytical balance, micro analytical balance and semi-micro analytical balance); The electro-optical balance is equipped with air damping device or electromagnetic damping device, which makes the balance have high sensitivity and can quickly prevent the beam from shaking. The photoelectric balance can't see the weight from the appearance, but it can see the weighing plate where the measured object is placed. The addition and subtraction of weight is operated by rotating dial, and the weighing value can be read directly by projection scale.