Text-Book of Medical Chemistry; For Medical and Pharmaceutical Students and Practitioners (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: 0r the velocities of the molecules are to each other inversely as the square roots of their densities, which corresponds to the statement of Graham's law. The densities of hydrogen and oxygen are known to be 1 and 16 respectively, and, therefore, the velocities of their molecules must be as the square roots of these numbers or as 4 to 1; or the molecule of hydrogen must move 4 times as fast as that of oxygen. The comparative velocities of other molecules may be calculated in the same way, from their densities. 22. Nature of Heat.?As nearly as we can conceive, the phenomena and sensations to which we apply the term heat, are the manifestations to our senses of the motions of the molecules of matter, which we have partially discussed in the last sections. Besides producing the sensation of heat, it acts variously on bodies; it boils water, melts iron, makes the metals give out light, electricity, etc. It was formerly supposed that heat was a form of matter? a subtle fluid which could flow from one part of a body to another, or through the air. We still retain some of the forms of expression used while that theory was held; such as conduction, convection, absorption, emission, radiation, etc., the theory itself being entirely abandoned. We now regard heat as a manifestation of one form of molecular motion. The more rapid the motion of the molecules of any given body, the higher will be the temperature. Many of the phenomena of heat may be beautifully illustrated by means of a ball attached to an elastic India rubber string, held in the hand. The ball may represent the molecule, the string the elastic cohesive force, which acts between molecules, and the force applied by the hand to make the ball revolve about it, the force of heat. 23. The Sources of Heat are the sun, st...