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Encyclopedia Britannica - Main :: GOA-GRA |
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GRAHAM, THOMAS (1805-1869) , British chemist, born at Glasgow on the loth of December 1805, was the son of a merchant of that city. In 1819 he entered the university of Glasgow with the intention of becoming a minister of the Established Church. But under the influence of Thomas Thomson (1773-1852), the professor of chemistry, he developed a taste for experimental science and especially for molecular physics, a subject which formed his main preoccupation throughout his life. After graduating in 1824, he spent two years in the laboratory of Professor T. C. Hope at Edinburgh, and on returning to Glasgow gave lessons in mathematics, and subsequently chemistry, until the year 1829, when he was appointed lecturer in the Mechanics' Institute. In 183o he succeeded Dr Andrew Ure (17781857) as professor of chemistry in the Andersonian Institution, and in 1837, on the death of Dr Edward Turner
work
in the foundation of the London Chemical and Cavendish societies, and served as first president of both, is 1 and 1846. Towards the close of his life the presidency of t Val Society was offered him, but his failing health cause' ;to decline the honour. Graham's work
for the simplicity of the methods employed 'ining most important results. He communicated papers t `losophical Society of Glasgow before the work of that so( 's recorded in Transactions, but his first published paper ,he Absorp- tion of Gases by Liquids," appeared in the An Philosophy for 1826. The subject with which his name i :ominently associated is the diffusion of gases. In his per on this subject (1829) he thus summarizes the kno' experiment had afforded as to the laws which regulate ovement of gases. " Fruitful as the miscibility of gase. peen in in- teresting speculations, the experimental infor i we possess on the subject amounts to little more than the well-established fact that gases of a different nature when brought into contact do not arrange themselves according to their density, but they spontaneously diffuse through each other so as to remain in an intimate state of mixture for any length of time." For the fissured jar of J. W. Dobereiner he substituted a glass tube closed by a plug of plaster of Paris, and with this simple appliance he developed the law now known by his name " that the diffusion rate of gases is inversely as the square root of their density." (See DIFFUSION.) He further studied the passage of gases by transpiration through fine tubes, and by effusion through a minute hole in a platinum disk, and was enabled to show that gas may enter a vacuum in three different ways: (1) by the molecular movement
double
palladium , and proved that gases pass through these septa neither by diffusion nor effusion nor by transpiration, but in virtue of a selective absorption which the septa appear to exert on the gases in contact with them. By this means (" atmolysis ") he was enabled partially to separate oxygen from air.His early work on the movements of gases led him to examine the spontaneous movements of liquids, and as a result of the experiments he divided bodies into two classescrystalloids, such as common salt, and colloids, of which gum-arabic is a type the former having high and the latter low diffusibility. He also proved that the process of liquid diffusion causes partial decomposition of certain chemical compounds, the potassium sulphate, for instance, being separated from the aluminium sulphate in alum by the higher diffusibility of the former salt. He also extended his work on the transpiration of gases to liquids, adopting the method of manipulation devised by J. L. M. Poiseuille. He found that dilution with water does not effect proportionate alteration in the transpiration velocities of different liquids, and a certain determinable degree of dilution retards the transpiration velocity. With regard to Graham's more purely chemical work, in 1833 he showed that phosphoric anhydride and water form three distinct acids,- and he thus established the existence of polybasic acids, in each of which one or more equivalents of hydrogen are replaceable by certain metals (see Anna). In 1835 he published the results of an examination of the properties of water of crystallization as a constituent of salts. Not the least interesting part of this inquiry was the discovery of certain definite salts with alcohol analogous to hydrates, to which the name of alcoholates was given. A brief paper entitled " Speculative Ideas on the Constitution of Matter " (1863) possesses special
interest
movement
Graham's Elements of Chemistry, first published in 1833, went through. several editions, and appeared also in German, remodelled, under J. Otto's direction. His Chemical and Physical Researches were collected by Dr James Young
Smith
Smith
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