Basic components of a simple optical microscope

At a much higher level of sophistication is the SEM. Although the SEM is an awesome instrument (Fig. 4.2) capable of extremely high magnification (25,000x compared to l,000x for optical microscopes), its utility for the archaeologist 

Elemental analysis involves measuring the composition of materials to determine 

The foundations of the modem science and the systematic investigation of the elements began in the Arabic world where experiments with scientific questions were well underway in the ninth-century ad. Jabir ibn Hayyan, one of the founding fathers of chemistry, was bom in Persia and a prolific scholar. He emphasized experimentation and invented a wide variety of laboratory equipment, as weU as a number of fundamental processes such as distillation and crystallization. He discovered and described many basic chemical substances - including hydrochloric and nitric acid, and the elements arsenic, antimony and bismuth - that are the basis of chemistry today. He was the first to purify and isolate sulfur and mercury as pure elements. He began to systematically describe the basic elements and provided the framework for the periodic table by distinguishing metals and nomnetals in his classification. 

The periodic table is the contribution of a Russian scientist, Dmitri Mendeleev, who organized a long list of known chemical elements into a systematic framework in 1869 with 66 known elements. Mendeleev arranged the elements by mass and other properties and predicted the existence of new elements in his table based on the repetitive patterns he observed (the periodic behavior of the elements). This table of elements has now grown to more than 100 and new discoveries continue to be made, although only 90 are naturally occurring and of potential archaeological interest. 

More common methods for elemental analysis - to determine the elemental contents of a sample - include spectroscopy and spectrometry. Spectroscopy measures changes in atoms that cause a specific light photon to be either absorbed (absorption spectroscopy) or emitted (emission spectroscopy). This light has a precise wavelength or energy, characteristic of a specific element in the periodic table. The simplest (and oldest) form of elemental analysis was not spectroscopic, in fact, but colorimetric. This method was based on the reaction of a strongly colored chemical in a solution. The appearance of a specific color in the solution revealed the identity of the element of interest. If the color intensity is proportional to the amount of that element present, the method can also be used to estimate the amount of the element present. 

---