On the one hand, the student has been informed by some writers that the only certain way lies in the use of the entropy-function and the thermodynamic potentials; on the other hand, he is told with equal authority that the method used by the original investigators has been the consideration of cyclic processes, and that the former method is nothing but a mathematical (perhaps unnecessary) refinement of the results obtained by the latter. These extreme attitudes appear to me to be unfortunate, and more especially when one observes the physical clearness introduced by the use of cyclic processes, but at the same time remembers that most of the results obtained by separate investigators using cyclic processes had, with a great many more, previously been found by J. Willard Gibbs by means of a purely analytical method.

Some recent short publications on Chinese gunpowder and firearms are misleading... I have had valuable assistance from Dr. J. Needham... If the dates of the texts are correct, the discovery of the use of saltpetre in explosives and the development of gunpowder are to be sought in China from the eleventh century. The history of gunpowder is associated with that of saltpetre, no comprehensive account of which was available.

The Greek chemical treatises contain... a great amount of practical chemical information... fusion, calcination, solution, filtration, crystallization, sublimation and especially distillation; and methods of heating include the open fire, lamps, and the sand and water baths. Nearly all this practical knowledge... the Arabs... derived... from the very source we are now considering.

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A great number of our common ideas and ways of looking at the world were really shaped for us by the Greeks of antiquity, and... incorporated into the scientific knowledge of today. Such ideas as those of matter, force, element, number, space, time, etc., came to us from the ancient Greeks.

The earliest chemical theory was qualitative in the strictest sense; the so-called Aristotelean doctrine of the four elements assumed that air, water, earth, and fire, were qualities impressed on a primal matter; and the changes of material bodies were explained by the assumption that properties could be taken up by, and impressed upon, or removed from, the base-stuff. Transmutation as a possibility followed at once, and centuries of vain endeavour were required to impress the fact of its impossibility, leading to the true concept of element.

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The extension of Black's method by the physicist Lavoisier led to the downfall of the purely qualitative theory of phlogiston, and gave to chemistry the true methods of investigation, and its first great quantitative law—the law of conservation of matter.

It is clear, however, that the distinguishing mark of the whole development of theoretical chemistry and physics is the elimination of the anthropomorphic elements, especially specific sense-impressions, from the concepts. This process is called by Prof. M. Planck the objectification of the physical system.

If the present volume will help towards the comprehension of the fundamental principles on which the science of thermodynamics rests, and also serve to bring home the importance of a knowledge of these principles in the suggestion and interpretation of experimental work, the purpose which has been kept in view during its preparation will have been amply fulfilled. In any case, it is hoped that neither the extreme view that thermodynamic principles alone suffice in the construction of a systematic physical or chemical science, nor the equally mistaken opinion that they are of little practical utility to the experimental worker, can fairly result from its study.

There are not wanting, even to-day, chemists who advocate "purely chemical" methods in chemistry, and cannot appreciate the value of physical evidence in conjunction with mathematical calculations. We can only hope that their number is decreasing exponentially with time.

The first clear expression of the idea of an element occurs in the teachings of the Greek philosophers. ...Aristotle ...who summarized the theories of earlier thinkers, developed the view that all substances were made of a primary matter... On this, different forms could be impressed... so the idea of the transmutation of the elements arose. Aristotle's elements are really fundamental properties of matter... hotness, coldness, moistness, and dryness. By combining these in pairs, he obtained what are called the four elements, fire, air, earth and water... a fifth, immaterial, one was added, which appears in later writings as the quintessence. This corresponds with the ether. The elements were supposed to settle out naturally into the earth (below), water (the oceans), air (the atmosphere), fire and ether (the sky and heavenly bodies).

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Side by side with the production of metals, the Egyptians and the inhabitants of Mesopotamia perfected the arts of making glazed pottery... and the production of glass. ...vessels were baked in tall closed furnaces. "Egyptian blue" was made in Egypt by heating silica with malachite and lime... applied with soda as a blue glaze on faience, and the blue glass is also colored with copper. Some early... Egyptian and Babylonian blue glass are coloured with cobalt.