Chemical substances pure, laboratory

Object of the Course.—In the laboratory exercises which constitute the working portion of this text, directions are given for the preparation of a number of chemical substances in more or less pure condition. 

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. 

By contrast, in the area of investigation mapped by chemical tables, components meant entities that were both imperceptible parts of chemical compounds and perceptible substances that could be separated from compounds and manipulated as ordinary materials in the laboratory. When separated from a salt, for example, the component vitriolic acid was no less an ordinary chemical substance than the compound, the salt—despite the fact that eighteenth-century chemists, too, conceived of components as agents that caused the properties of the compound. The ontological status of components and compounds was exactly the same. This understanding was embedded in chemists analytical practice—the fact that chemical analysis actually took apart compounds such as salts, isolated their components in a pure form, and resynthesized the original compound from the components. Whatever the more specific definitions of substance components such as acids, alkahs, earths, and metals were in the eighteenth century, the existence of such kind of components was never... 

In chapter 10 we will finally come back to the Tableau s classification and try to assess its achievements on the basis of the historical insights obtained in the previous chapters. In particular, we will try to determine precisely which of its features were shaped by Lavoisier s new chemical system and which were not. However, we will arrive at the conclusion that the new chemistry shaped essential features of this classification only on the basis of a classificatory deep structure underlying both the phlogistic and the anti-phlogistic conceptualizations of pure laboratory substances. The chapter will close by addressing some questions of nomenclatural reform that we had to leave unanswered until the completion of our analyses. 

Our outline of chemical operations using pure chemical substances in sixteenth- and seventeenth-century metallurgy and pharmaceutical salt production shows that the chemistry of pure substances was a domain of chemical practice no less than of theory. It existed in workshops and artisanal laboratories and never became an exclusively academic subject. As is characteristic of chemistry in general, the workshop and the laboratory were by no means different worlds separated from each other. In eighteenth-century chemistry, materials, instruments, techniques, experiences, and conceptual knowledge flowed continuously back and forth from artisanal to academic sites. The men who inhabited these worlds ceaselessly crossed these boundaries as... 

In the table the concentration of the chemical is shown in percent. Values of 100% refer to the pure substance in dry or liquid form. Concentrations less than 100% refer to water solutions of the chemical. The other column in the table indicates whether or not a test under actual operating conditions is warranted. A "Yes" in this column means that magnesium is basically resistant to the chemical or that laboratory tests have shown enough promise to warrant testing under actual service conditions. 

Substances prepared under carefully controlled conditions and using very pure chemicals, in a modern laboratory, for example, contain only the basic component elements, those that determine the actual composition and nature of the substances. Natural substances, whether of mineral or biological origin, and also most synthetic (human-made) substances contain, in addition to their main components, impurities foreign to their basic composition. Most impurities usually enter substances such as minerals, for example, in relatively small amounts, when the substances are created. Others, such as those in some rocks and the wood of trees, do so in the course of their existence. Once within a substance, impurities become an integral part of the host substance and impair the purity of the substance. Although they alter the actual composition of substances, impurities do not affect their basic properties. 

The variety of substances that humans are exposed to, both pure chemicals and mixtures, are being assayed for mutagenicity by hundreds of laboratories, e.g., water supplies, (Chapter 6, this volume), soot from city air, hair dyes (7) and cosmetics, drugs, food additives, food, molds, toxins, pesticides, industrial chemicals, and fumigants. 

PCP is a completely artificial substance. That is, it is not derived from anything in nature it is made purely from industrial chemicals. In fact, police are often tipped off to the presence of an illegal PCP laboratory when neighbors complain of terrible chemical smells or when careless criminals create chemical fires and explosions. 

This example is of a traceability [1] protocol [2] for the chemical measurement of an element by a primary method of measurement [3]. It can be used for the certification of a single-element reference material by a national reference laboratory. This protocol relates to a very pure strontium nitrate solution, stabilized by 10% (by volume) nitric acid1. This solution is to be certified for the amount of strontium substance n(Sr) per unit mass of aqueous solution m (sol). The general measurement method described is based in part on the experience of certifying a currently available certified reference material (CRM) [4], Standard Reference Material (SRM) 3153a [5],... 

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