120 



CHEMISTEY. 



dous appetites seem to separate them from the 

 higher forms of animals, but this distinction is 

 only comparative. It must be borne in mind that 

 an animal like a sheep, for example, converts 

 much of its food into carbonic acid, hippuric 

 acid, and water, thus utilizing the whole of the 

 potential energy, while the micro-organism, as 

 a rule, utilizes only a small portion. Those 

 micro-organisms which have been studied pro- 

 duce, like the higher animals, perfectly definite 

 chemical changes. Principal Dallinger re- 

 marked, in reference to the attempted distinc- 

 tion between the lower animal and vegetable 

 forms, that in following out the life-history of 

 certain monads he had used a nutritive fluid 

 containing no albuminoid substances, but only 

 mineral salts and tartrate of ammonium, and 

 that organisms classed as animals by Prof. 

 Huxley were found to live in that mineral 

 fluid. Bacteria of forms which can not be dis- 

 tinguished by the microscope have very dif- 

 ferent physiological functions. They can be 

 modified physiologically, but not at all readily 

 morphologically. By a slow change it is pos- 

 sible completely to reverse the conditions of the 

 environment of the bacterium without chang- 

 ing its form. 



In a special discussion in the British Associ- 

 ation on "The Constitution of the Elements," 

 Prof. Dewar remarked that Deville has shown, 

 by his researches on dissociation, that in com- 

 pound substances there is an equilibrium be- 

 tween decomposition and recomposition, this 

 balanced relation changing with the tempera- 

 ture. The breaking up of the iodine molecule, 

 effected by Victor Meyer, is a decomposition 

 of elementary matter, but, owing to the rapid 

 recomposition, there seems no hope of isolating 

 atomic iodine at low temperatures. The vapors 

 of potassium and sodium have different densities 

 at different temperatures ; probably, also, their 

 molecules consist of two atoms at lower and 

 of one atom at higher temperatures. More ex- 

 act determinations are needed of those sub- 

 stances which exhibit a variable vapor densi- 

 ty. The evidence afforded by spectral analysis 

 proves that oxygen and nitrogen have two 

 spectra, and therefore probably different mol- 

 ecules at different temperatures. Hydrogen 

 has a complicated spectrum under certain con- 

 ditions. Mr. Lockyer has proved that the iden- 

 tity of certain " basic " lines of different ele- 

 ments, such as iron and calcium, is not due to 

 impurity, but the greater dispersion of more 

 powerful instruments has shown that the coin- 

 cidence of these lines is only apparent, and not 

 absolute. The differences observed in some of 

 the spectrftl lines of a single element in the 

 sun might be accounted for not by the decom- 

 position of the " element " into simpler matter, 

 but by great differences of level in the luminous 

 vapor. Prout's hypothesis, that the atomic 

 weights of the other elements are multiples of 

 that of hydrogen, has no basis in experimental 

 faot. Prof. Wolcott Gibbe remarked upon the 

 probability that what is generally regarded as a 



simple molecule, such as sodium chloride, con- 

 sists in the solid state of several hundreds of 

 atoms, and that the salt undergoes, in solution, 

 a kind of molecular dissociation. Very com- 

 plex molecules, such as those acids he had pre- 

 pared containing many molecules of the oxides 

 of molybdenum, vanadium, barium, etc., are 

 probably derived by substitution from what 

 are called simple molecules, but which are 

 really composed of a great number of atoms. 



Chemical Physics. Troost has recently shown 

 that oxygen gas is capable of passing through 

 silver at a red heat, in the same manner as 

 hydrogen behaves with platinum and iron. A 

 tube of pure silver was inclosed in a platinum 

 cylinder, and the whole heated in the vapor 

 of boiling cadmium. On exhausting the sil- 

 ver tube with a Sprengel pump, and passing 

 oxygen into the space around it, the gas was 

 found to enter at a rate corresponding to 1'7 

 litre per hour for each square metre of surface 

 exposed. On passing air instead of oxygen 

 into the outer chamber, oxygen with only a 

 trace of nitrogen was found in the interior, but 

 the rate of transfusion was diminished nearly 

 one half. Instead of exhausting the tube, it 

 was found necessary only to pass through it 

 slowly a stream of some other gas, such as car- 

 bon dioxide ; but this considerably lessened the 

 rate of transfusion. The oxygen was replaced 

 by other gases, such as carbon dioxide, car- 

 bon monoxide, and nitrogen, but they passed 

 tnVough the walls of the tube with extreme 

 slowness. The author suggests that this prop- 

 erty of silver may some time be utilized to ex- 

 tract oxygen direct from the atmosphere. 



W. Spring has investigated the cause of the 

 different specific gravities of one and the same 

 metal according as it has been cast, rolled, 

 drawn into wire, or hammered ; whether the 

 difference observed proves a real condensation 

 of the matter under the action of pressure, or 

 is merely due to the expulsion by pressure ot 

 gases which have been occluded when the 

 ingot was cast. According to well-known re- 

 searches, metals, such as platinum, gold, silver, 

 and copper, which have been proved to oc- 

 clude gases on fusion, and to let them escape 

 incompletely on solidification, are precisely 

 those which are most increased in their specific 

 gravity by pressure. He has submitted to 

 pressures of about 20,000 atmospheres, metals 

 which possess this property either not at all 

 or to a very trifling extent, and he finds that 

 though a first pressure produces a slight perma- 

 nent increase of density, its repetition makes 

 little difference. Hence the density of solids, 

 like that of liquids, is only really modified by 

 temperature. Pressure effects no permanent 

 condensation of solid bodies, except as they are 

 capable of assuming an allotropic condition of 

 greater density. The limit of elasticity of a 

 solid body is the critical moment when the 

 matter begins to flow under the action of the 

 pressure to which it is submitted, just as, for 

 example, ice at or below C. may be liquefied 



