90 EFFLUX OF LIQUIDS THROUGH TUBES. hydrobromic acid, seemed to have any influence; whilst the hydrosulphuric and hydrocyanic acids, and a few of the salts of potassium and ammonium-viz., the nitrates of potassium and ammonium, chlorides of potassium and ammonium, the iodide, bromide, and cyanide of potassium-increased the rapidity of the flow but it is remarkable, that concentrated solutions of iodide of potassium above a temperature of 140° F., and of nitrate of potassium above 104°, actually flow more slowly than distilled water does. Strict attention to the temperature at which these comparisons are made is absolutely necessary, for both with water and with dilute solutions generally, a slight elevation of temperature produces a great increase in the rapidity of efflux. Water, for instance, at 113°, escaped through the same tube with a rapidity 2 times as great as it did at 41°. Hitherto no connexion has been traced between the rate of efflux of the liquid and its density, capillarity, or fluidity. The capillarity of alcohol, as well as its density, increases in proportion as it is diluted with water, while its fluidity diminishes; but experiment has proved that a mixture of equal parts of spirit of wine and water flows out with considerably less than half the rapidity of pure alcohol, and with less than one-third of that of distilled water. The dilution of alcohol, therefore, to a certain point, retards its efflux, and beyond that point increases it: the minimum rate of efflux corresponds with that particular mixture of alcohol and water, which is attended with the maximum of contraction after admixture of the two liquids. The degree of solubility of a body in water appears to exercise but a secondary influence on the phenomenon. Poiseuille shows it to be highly probable that the various solutions, when introduced into the blood of a living animal, provided that they do not cause the serum to coagulate, produce effects of acceleration or retardation on the capillary circulation, corresponding with those which are observed with the same liquids in capillary tubes of glass. He has proved this to be the case by direct experiment, with the iodide of potassium when injected into the veins of the horse; and has shown that when various salts are mingled with serum, and the liquids are allowed to flow out through small tubes, retardation or acceleration occurs, as in the corresponding cases with their aqueous solutions. The following table contains several of Poiseuille's results, numerically expressed. The solutions employed contained 1 per cent. of the various substances mentioned, except in the case of the last four liquids. They were exposed to a pressure equal to EFFLUX OF LIQUIDS THROUGH TUBES. 91 that of a column of water I metre (39:37 inches) in height, at the temperature of 52°16, unless otherwise noted; and escaped through a tube 64 millimetres (2.519 inches) in length, and O'24946mm. (00108 inch) in diameter. The numbers in the table indicate the time occupied in seconds, for the efflux of equal bulks of the liquids used-viz., 6.6 cubic centimetres (0'4 cubic inch). The observation of Poiseuille, that diluted alcohol has a point of maximum retardation coincident with the degree of dilution at which the greatest condensation of the mixed liquids occurs, or at a point in which I atom of alcohol and 3 atoms of water (H2O) are present in mixture, served as a starting point to Graham for a new inquiry. (Phil. Trans. 1861, p. 373.) The rate of transpiration he has proved to be, in certain cases, connected with chemical composition. The 3-atom hydrate of methylic alcohol, although not distinguished by any particular degree of condensation in volume, exhibits a peculiarity in its transpiration-rate similar to that of dilute vinic alcohol. The hydrated acids, also, in many cases, exhibit a characteristic retardation of transpiration at a particular degree of hydration. As a result of these inquiries, Graham also concludes that as far as his observations upon different alcohols, ethers, and acids, extend, the order of succession of individual substances in any homologous 92 FLOW OF LIQUIDS-SOLUTION OF GASES. series would be indicated by the degree of transpirability of these substances as clearly as it is by their comparative volatility. In hydrated substances, the extent to which transpiration is affected by the annexation of water, is by no means in proportion to the intensity of combination. In sulphuric acid, for instance, the maximum transpiration time occurs with the hydrate (H2SO4 + H2O), of acetic acid with the compound (HC2H ̧O2+H2()), of nitric acid with (2 HNO3+3H,O), and with alcohol with the hydrate (CHO+ 3H2O). 2 2 2 The following table contains a résumé of some of the more interesting results obtained by Graham upon this subject. The transpiration time of water at the particular temperature employed is, in all cases, taken as the unit of comparison : ... Nitric Acid (HNO1) ... 09899 21.6514 + H2O 2'1034 23'7706 0'4010 +61,0 1'6040 Butyrate of Ethyl Acetic Acid (HC2H2O)... (64) Adhesion of Gases to Liquids. The adhesion of gases to liquids, although not quite so evident as that of solids to liquids, is yet attended with results almost equally important. It is exemplified in the pouring of liquids from one vessel to another, by the bubbles which are carried down with the descending stream, and which rise and break upon the surface of the liquid. Adhesion, however, produces in the effects of solution which attend the mutual action of gases and liquids, results which are far more general in their operation. All gaseous bodies are in a greater or less degree soluble in water: some, as hydrochloric acid and ammonia, being absorbed by it with extreme rapidity, the liquid taking up 400 or 600 times its bulk of the gas; in other instances, as occurs with carbonic acid, water takes up a volume equal to its own; whilst in the case of nitrogen, oxygen, and hydrogen, it does not take up much more than from to of its bulk. As the elasticity of the gas is the power which is here ABSORPTION OF GASES BY LIQUIDS. 93 opposed to adhesion, and which at length limits the quantity dissolved, it is found that the solubility of each gas is greater, the lower the temperature, and the greater the pressure exerted upon the surface of the liquid. Dr. Henry found that at any given temperature, the volume of any gas which was absorbed was uniform, whatever might be the pressure; consequently that the weight of any given gas absorbed by a given volume of any liquid at a fixed temperature increased directly with the pressure. If the pressure be uniform, the quantity of any given gas absorbed by a given liquid is also uniform for each temperature; and the numerical expression of the solubility of each gas in such liquids is termed its coefficient of absorption, or of solubility, at the particular temperature and pressure; the volume of the gas absorbed being in all cases calculated for 32° F., under a pressure of 29.92 inches of mercury. Thus 1 volume of water at 32°, and under a pressure of 29'92 inches of the barometer, dissolves 004114 of its volume of oxygen; and this fraction represents the coefficient of absorption of oxygen at that temperature and pressure. All water contains a certain small proportion of air in solution, in consequence of the solubility of the gases of which the atmosphere consists; and if placed in a vessel under the airpump, so as to remove the atmospheric pressure from its surface, the dissolved gases rise through the liquid in minute bubbles. Small as is the quantity of oxygen thus taken up by water from the atmosphere, it is the means of maintaining the life of all aquatic plants and animals; if the air be expelled from water by boiling, and it be covered with a layer of oil to prevent it from again absorbing air, fish or any aquatic animals placed in such water quickly perish. Even the life of the superior animals is dependent upon the solubility of oxygen in the fluid which moistens the airtubes of the lungs, in consequence of which this gas is absorbed into the mass of the blood as it circulates through the pulmonary vessels. If a mixture of two or more gases be placed in contact with a liquid, a portion of each gas will be dissolved, and the amount of each so dissolved will be proportioned to the relative volume of each gas in the mixture multiplied into its coefficient of solubility at the observed temperature and pressure :-For instance, if it be assumed in round numbers, that atmospheric air contains th of its bulk of oxygen, and ths of its bulk of nitrogen, the amount of each of these gases which water should absorb from the air at a temperature of 59° under a pressure of 29'92 inches, may be calculated in the following manner. The coefficient of absorption. for oxygen at 59° is o'02989, that of nitrogen is 0.01478: 91 ADHESION OF GASES TO LIQUIDS AND SOLIDS. = 002989 000597 proportion of oxygen dissolved. 001478 = 0.01182 proportion of nitrogen dissolved. O'01779 proportion of air dissolved. The proportion of nitrogen thus required by calculation is rather less than double that of the oxygen, or 66'1 : 33'9, a proportion which agrees almost exactly with the results of experiment. The following table shows the solubility of some of the principal gases, both in water and in alcohol (Bunsen, Liebig's Annal., xciii. 1, and Carius, Ib. xciv. 129). All these gases, with the exception of hydrochloric acid, may be expelled from the water by long-continued boiling. Solubility of Gases in Water and in Alcohol. Other liquids besides water dissolve the gases with greater or less avidity. (65) Adhesion of Gases to Solids.-When iron filings are gently dusted over the surface of a vessel of water, a considerable body of iron dust may be accumulated upon the surface, until at length it falls in large flakes, carrying down with it bubbles of air of considerable size. The adhesion of these bubbles caused the particles of iron to float, for such particles are nearly eight times as heavy as water. Contrasted with this result is the effect of dusting magnesia in fine powder over the surface of water; the particles, although not one-third of the density of the iron, immediately become moistened and sink. In consequence of this adhesion of air to their surface, many small insects are enabled to |