Amorphous Residues and Adhesives

Amorphous organic substances can survive in other contexts, such as on stone tools, or as isolated

Figure 2 Partial gas chromatograms comparing the wax ester distribution in (A) Neolithic deposit on a potsherd from Ergolding Fischergasse, Germany with (B) authentic beeswax (Apis melli-fera). Peak identities: 1 -6 are wax esters in the range C40 (peak 1) to C50 (peak 6) comprising mostly hexadecanoic (palmitic) acid esterified with alcohols of increasing chain length (C24 to C34). Peaks At to A5 represent co-elution of hydroxymonoester isomers and are seen in both samples. In contrast, peaks *., to *5 are only present in the authentic sample and represent wax esters comprising an unsaturated (octadecanoyl) fatty acid moiety. Their absence in the ancient samples is not unexpected given the susceptibility of the double bond to oxidation or reduction reactions. Reproduced with permission from Heron C, Nemcek N, Bonfield KM et al. (1994). The chemistry of Neolithic beeswax. Naturwissenschaften 81: 266-269. Courtesy of Springer Verlag.

Figure 2 Partial gas chromatograms comparing the wax ester distribution in (A) Neolithic deposit on a potsherd from Ergolding Fischergasse, Germany with (B) authentic beeswax (Apis melli-fera). Peak identities: 1 -6 are wax esters in the range C40 (peak 1) to C50 (peak 6) comprising mostly hexadecanoic (palmitic) acid esterified with alcohols of increasing chain length (C24 to C34). Peaks At to A5 represent co-elution of hydroxymonoester isomers and are seen in both samples. In contrast, peaks *., to *5 are only present in the authentic sample and represent wax esters comprising an unsaturated (octadecanoyl) fatty acid moiety. Their absence in the ancient samples is not unexpected given the susceptibility of the double bond to oxidation or reduction reactions. Reproduced with permission from Heron C, Nemcek N, Bonfield KM et al. (1994). The chemistry of Neolithic beeswax. Naturwissenschaften 81: 266-269. Courtesy of Springer Verlag.

aggregates. An example is birch bark tar, which has been used as multipurpose natural product for at least 10 000 years, and its use continues to the present day in some parts of eastern and south-eastern Europe. The tar is obtained by heating fresh birch bark (Betula sp.) at temperatures of 250-350°C. Spectroscopic and chromatographic investigations of the material began during the 1960s, and a variety of techniques such as TLC, infrared and nuclear magnetic resonance (NMR) spectroscopy were used to identify birch bark tar on flint implements, lithics, ceramic and lumps of tar with human tooth impressions. More recent analysis has revealed that the tar was used to glue flint tips to arrows belonging to Otzi - the 'ice man' discovered in the Tyrolean Alps in 1991. The tar has also been identified on potsherds, stone implements and worked bone from Ergolding Fischergasse (mid 4th millennium bc).

Many of the early analyses have recently been confirmed by GC-MS, including lumps with tooth impressions, interpreted as a very early form of chewing gum.

Figure 3 compares fresh birch bark tar with samples from the Mesolithic site of Star Carr (Yorkshire, UK). The triterpenoids of the outer bark of Betula sp. are derivatives of lup-20(29)-ene and, to a lesser extent, olean-2-enes. The triterpenoid composition is modified slightly by heating the bark and by some 9000 years of water-logged burial, but the identity and relative abundance of these biomarkers is sufficient to characterize the archaeological samples. Tars produced from other bark and wood samples have a very different molecular composition. For example, softwoods produce diterpenoid compounds and are easily distinguishable, while the barks and tars of other trees such as hazel, rowan and willow produce triterpenoids but with different carbon skeletons or relative abundance of the lup-20(29)-enes. Analysis by GC-MS enables identification of the molecular markers of the heating of the bark and post-depos-itional alteration (Figure 4).

Bitumen represents the fraction of sedimentary organic matter which is soluble in organic solvents. The liquid or semi-solid varieties of bitumen were widely used in the Near East and Middle East in antiquity, serving as a multipurpose glue and water-proofing material, a building mortar, medicinal agent and as one of the constituents of the organic preparations applied to mummified bodies in Ancient Egypt. Compounds consistent with a bituminous substance include saturated hydrocarbons which have linear (al-kylated alkanes) or cyclic (steranes, terpanes) carbon skeletons. These molecules largely derive from microscopic plants deposited in the sediments as well as bacterial inputs. It has proved possible to identify molecular and isotopic characteristics of the bitumen, which enables archaeological finds to be assigned to a particular source of bitumen. At the site of Susa, Iraq (dating from the beginning of the 4th millennium bc), bitumen was deliberately mixed and heated with mineral elements, to produce a substance known as bitumen mastic - a product ideal for fashioning decorative objects by sculpture.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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