Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/43

Rh through each other so as to remain in an intimate state of mixture for any length of time." For the fissured jar of Priestley and Döbereiner he substituted a glass tube closed by a plug of plaster of Paris, and with this simple appliance he developed his now well-known law "that the diffusion rate of gases is inversely as the square root of their density."

With regard to the special importance of Graham's law to the chemist and physicist, it may be sufficient to point out that a great number of chemical as well as physical facts are co-ordinated by the assumption that all substances in the state of gas have the same molecular volume or contain the same number of molecules in a given space (Avogadro's law); and, in the second place, it has become evident that the phenomena of heat are simply the manifestations of molecular motion. According to this view the absolute temperature of a gas is proportional to the vis viva of its molecules; and since all molecules at a given temperature have the same vis viva, it follows that the molecules must move with velocities which are inversely proportional to the square roots of the molecular weights. Moreover, since the molecular volumes are equal, and the molecular weights are therefore proportional to the densities of the aeriform bodies in which the molecules are active units, it also follows that the average velocities of the molecules in any two gases are inversely proportional to the square roots of their respective densities. Thus the simple numerical relations first ob served in the phenomena of diffusion are the direct result of molecular motion, and it is now seen that Graham's empirical law is included under the fundamental law of motion.

Graham also studied the passage of gases by transpiration through fine tubes, and by effusion through a minute hole in a platinum disc, and was enabled to show that gas may enter a vacuum in three different ways: (1) by the molecular movement of diffusion, in virtue of which a gas penetrates through the pores of a disc of compressed graphite; (2) by effusion through an orifice of sensible dimensions in a platinum disc (the relative times of the effusion of gases in mass being similar to those of the molecular diffusion, although a gas is usually carried by the former kind of impulse with a velocity many thousand times as great as is demonstrable by the latter); and (3) by the peculiar rate of passage due to transpiration through fine tubes, in which the ratios appear to be in direct relation with no other known property of the same gases,—thus hydrogen has exactly double the transpiration rate of nitrogen, the relation of those gases as to density being as 1: 14.

He subsequently examined the passage of gases through septa or partitions of india-rubber, and plates of non-crystalline metals such as palladium, and proved that gases pass through these septa neither by diffusion, effusion, nor transpiration, but in virtue of a selective absorption which the septa appear to exert on the gases in contact with them. By this means he was enabled partially to separate oxygen from air, and to calculate the density of metallic-hydrogen from the remarkable expansion which attends the absorption of hydrogen by palladium. The experiments led him to believe that palladium with its occluded hydrogen was an alloy, a view that has been greatly strengthened by the recent experiments of MM. Cailletet and Pictet.

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 classes,—crystalloids, 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, by a series of beautiful experiments, that the process of liquid diffusion actually causes partial decomposition of certain chemical compounds, the sulphate of potash, fat instance, being separated from the sulphate of alumina 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 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. Thus in the case of alcohol the greatest retardation is with six equivalents of water, nitric acid with three, and acetone with as much as twelve equivalents.

It is only possible here to indicate the prominent features of Graham's more purely chemical labours. In 1833 he showed that the various compounds of phosphoric acid and water constitute distinct salts, in each of which the hydrogen may be displaced by other metals. He was the first, therefore, to establish the existence of polybasic compounds, in each of which one or more equivalents of hydrogen are replaceable by certain metals, and he further showed that by heating biphosphate of soda a metaphosphate is formed, and from this he obtained a corresponding hydrated acid. In 1824 he demonstrated that the spontaneous inflammability of one variety of phosphuretted hydrogen is due to its admixture with a very small proportion of an oxide of nitrogen, probably nitrous acid. In 1835 he published the results of an examination of the properties of water 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 deserves notice as possessing special interest in connexion with work done since Graham's death. In it he expressed the view that the various kinds of matter now recognized as different elementary substances may possess one and the same ultimate or atomic molecule in different conditions of movement.

Graham's work, viewed as a whole, is remarkable alike for its originality and for the singular simplicity of the methods employed in obtaining most important results.

 GRAHAME, (1765-1811), author of The Sabbath and other poems, was born at Glasgow, April 22, 1765. His father was a successful lawyer, and, by a very common error, he conceived that no other profession could be so suitable or so advantageous for his son. James, dutiful, and shrinking from opposition, as he did all through life, obeyed the parental wish, and after completing his literary course at the university of his native city, went in 1784 to Edinburgh where he studied law, first to qualify himself for the business of writer to the signet, and subsequently for the Scottish bar, of which he was elected a member in 1795. His inclinations, however, were all for retirement and literature; and finally, when he had reached the mature age of forty-four, he took orders in the English Church, and became curate first at Shipton, Gloucestershire, and then at Sedgefield in the county of Durham. He did not long enjoy an office which he adorned by his pious and eloquent ministrations. Ill health compelled him to try the renovating effects of his native air, but he died shortly after his return, September 14, 1811. The works of Grahame consist of a dramatic poem Mary Queen of Scots (published in 1801), The Sabbath (1804),