Chemical Instruments

Chemical instruments are pieces of laboratory equipment that are used to make quantitative measurements. They are distinguishable from chemical apparatus in that they directly measure quantities, or enable a quantity to be measured, whereas chemical apparatus are used solely in the conduction of experiments. For example, burettes and spectro photometers are chemical instruments--one measures volume and the other measures absorbance. Fractional distillation columns, Bunsen burners, and beakers on the other hand are chemical apparatus because they are used in conducting experiments, but do not measure any quantity.

Historically, the development of analytical techniques has closely followed the introduction of new chemical instruments. The first quantitative analyses were gravimetric analyses (weighing things) that were made possible by the invention of a precise balance. English physicist Francis Hauksbee (1666- 1713) constructed the first c hemical precise balance in 1710. In the 1770s, French chemist Antoine-Laurent Lavoisier (1743-1794) dismantled the phlogiston theory of combustion by accurately and precisely measuring the weight of the chemicals both before and after his experiments. This soon became the standard method of performing gravimetric a nalyses.

Chemical instruments were not solely introduced for increasingly ambitious experiments. Governments and other regulatory agencies also used them. For example, in 1789, English instrument maker Jesse Ramsden (1735-1800) made a balance for the purpose of measuring the specific gravity of water-alcohol mixtures to facilitate government tax legi slation.

Chemical instruments have become far more complex than their predecessor, the simple chemical balance. In modern laboratories, many chemical instruments are electrical. This began in the 1930s when a rapid development in electronics resulted in a major revolution in analytical chemical instrumentation. The basic task of electrical instrument s is to translate chemical information about a substance into a form that a chemist can directly observe. Electrical chemical instruments allow for the naturally unobservable, such as molecules, to be observed. Realizing the steps between the observer and the observable is important in order to understand the role of chemical instruments in modern laboratories. There are four main components to electrical instruments. 1) Signal generators allow for direct or indirect interaction of the substance being analyzed with some form of energy, such as electricity or light. 2) Input transducers, also known as detectors, are devices that transform the chemical or physical prope rty of the substance being analyzed into an electronic signal. 3) Signal modifiers are electronic components that perform operations, such as amplification and filtering, on the generated signal. 4) Output transducers convert the modified electrical signal into information that can be read, recorded, and interpreted by a chemist.

Consider the basic spectrophotometer as an example. This instrument is used widely in laboratories for analyzing a substance and its components based on its absorbance. The signal generator is the light that is shone on the substance. The input transducer is the photo detector that detects the radiation emitted from the radiated substance. T he signal modifier is the computing device that calculates the absorbance of the substance. And finally, the output transducer is the dial on the spectrophotometer itself that shows the absorbance of the substance. This process of finding the absorbance of a substance would be much more cumbersome without the use of electronically enhanced chemica l instruments.

Chemical instruments are useful in expanding the scope of our senses. Precise experiments cannot be conducted without knowing quantities. Instruments allow chemical and physical qualities that we cannot see, hear, smell, taste, or touch to be observed. With increased use of chemical instruments deeper probing of the properties and behavior of chemical substances is possible.