Ua 



1904.] 



KNOWLEDGE >.^- SCII-XTIFIC NEWS. 



35 



sun's rays and the powers of endurance to lieat of 

 corals and of Lithothaiimion, a point on which Darwin 

 had speculated. It seems that except the Poiitcs, all 

 other forms of coral succumbed within two hours' 

 exposure, and it was evident that the essential life-gift 

 alike to coral and plant was a constant supply of fresh 

 sea-water. 



Among the contributions to the monograph certainly 

 the most industrious of all is Dr. Hinde's report on his 

 examination of thin sections of the materials obtained 

 from the reef borings and those made beneath the lloor 

 of the lagoon. Upwards of 500 microscopic surface 

 slittings were prepared for diagnosis in Professor Judd's 

 geological laboratory at the Royal College of Science. 

 .\s already mentioned, the main boring, begun in 1897, 

 was taken down to 1114^ feet, and it may be added that 

 the diameters of the cores brought up in the drilling 

 apparatus were, top to 68 feet, about 4 inches; 68-210 

 feet, about 3J inches; 210 toboring limit, about 2| inches. 

 .\11 these cores ranged in length from i inch to 3 feet. 

 Dr. Hinde supplies an elaborate description of a detailed 

 inspection of the several lengths of core that were placed 

 under examination for the detection of organisms, and we 

 cannot do better than quote here Professor Judd s general 

 conclusion thereon, namely, that " from top to bottom the 

 same organisms occur, sometimes plants, sometimes fora- 

 minifera, and sometimes corals predominating ; but in the 

 whole depth bored the same genera and species of these 

 various groups of organisms take their part in the "build- 

 ing up of the mass." (Fig. 5). 



.\ large amount of space would be necessary to even 

 summarize the many points of research apart from 

 boring and sounding operations embraced by this truly 

 classic exploration in the far Pacilic. There was made, 

 however, we must not omit to mention, a magnetic sur- 

 vey by H.M.S. Penguin (Captain Field) ; a series of 

 meteorological observations ; and a thorough study of the 

 natural history of the island of Funafuti. 



The numerous helpers in the two continents have 

 reason to be proud of the evidence of their long-continued 

 efforts, and undoubtedly the scientific results of the sur- 

 vey will prove of the utmost value in current discus- 

 sions which concern the present-day re\ised \ iew of the 

 development of coral reefs. 



Modem Views of 

 Chemistry. 



By 11. J. H. Fenton, F.K.S. 



It may happen that there are some of our readers who 

 are interested in the study of Chemistry, but who have 

 not had the time or opportunity of following the very 

 rapid and important advances which have been made 

 in the science, especially in the departments of physical 

 and organic Chemistry. In the present articles, which 

 are addressed to readers of this class, it is proposed to 

 give brief sketches in outline of some of the more im- 

 portant developments which have occurred during recent 

 years. 



We will in the first place refer to the great changes 

 which have occurred in our views with regard to the 

 nature of solution and the chemical and physical changes 

 which may take place in dissolved substances ; the 

 advance of knowledge in this department has resulted in 

 what is sometimes called the •' New Cheniistr}-," which 



would scarcely be recognised as the same science by one 

 who had been a good chemist twenty-livf years ago, hut 

 who had not kept pace with the times. 



It may be mentioned in passing that it was the custom 

 formerly to restrict the term "solution" to liquid mix- 

 tures — that is to solids, liquiils, or gases dissolved 

 in licjuids; hut we may now speak of solutions of 

 gases in solids and even of solids in solids ; a solution 

 IS in fact, generally speaking, any homogeneous 

 mixture of two (or more) substances in which the pro- 

 portions may, within certain limits, be varied con- 

 tinuously. I'sually one speaks of one of the 

 constituents as the solvent and the other as the dissolved 

 substance or "solute " ; but this is only an arbitrary dis- 

 tinction. In the case of an aqueous solution of common 

 salt, for example, we might regard the mixture either as 

 a solution of salt in water or of water in salt; for if a 

 dilute solution be sufficiently cooled it becomes saturated 

 with respect to water, and solid water (ice) separates out, 

 leasing a stronger solution of salt, just as when a \'ery 

 strong solution is cooled it becotnes saturated with re- 

 spect to salt, and the latter separates in the solid state, 

 leaving a weaker solution of salt, i.e.. a stronger solution 

 of water. It was at one lime thought that solution con- 

 sisted in a sort of loose chemical combination between 

 the sohent and dissolved substance, and this idea seemed 

 to be supported by the fact that many salts and other sub- 

 stances combine with water to form definite hydrates, 

 which may be isolated in the crystalline form. But it 

 does not follow that tliese hydrates continue to exist 

 when the substance is in solution, and the probability is 

 that, in dilute solution at any rate, they do not exist. 



Certain membranes exist naturally, and may be pre- 

 pared artificially, which will allow water to pass through 

 them, but will not allow the passage of dissolved sub- 

 stances such as sugar, salt, &c. If now one separates a 

 solution of sugar from pure water by means of a mem- 

 brane of this kind water will pass both ways through the 

 membrane, but more will pass into the sugar solution 

 than out of it, so that its volume tends to become larger 

 and the solution weaker. If, however, the volume of the 

 solution IS kept constant, that is, if it is not allowed to ex- 

 pand, the pressure will increase instead, and will con- 

 tinue to do so until a certain maximum pressure is 

 reached. This maximum (osmotic) pressure depends 

 upon the temperature, the strength (or concentration) of 

 the solution, and the nature of the dissolved substance. It 

 is found to vary with the temperature and concentration 

 according to the same laws which regulate the pressure of 

 a gas, and, further, the actual pressure produced is the 

 same as that which would be exerted by the same sub- 

 stance (theoretically in the case of sugar) if it were in the 

 state of gas at the same temperature and volume. 



A large class of substances (such as sugar, urea, and 

 most other organic substances) behave, therefore, in 

 exactly the same way when dissolved in a solvent as 

 they would in the gaseous state — as regards the relations 

 between temperature, concentration, and pressure — only 

 that what we understand by " pressure " in the gas state 

 must be interpreted as "osmotic pressure" in the case of 

 solutions. 



By making use of Avogadro's hypothesis— that ecjual 

 \olumes of gases contain, at the same temperature and 

 pressure, the same number of molecules — we can com- 

 pare the molecular weights of gaseous elements or com- 

 pounds by weighing equal volumes of them under the 

 same conditions; and now by extending this hypothesis 

 to substances dissolved in liquids we can compare their 

 molecular weights in a similar way. It may be done in 

 the latter case by measuring (directly or indirectly) the 



