92 



NA TURE 



[May 28, 1908 



subjects, disigned primarily, as the introduction to the 

 Blue-book points out, to overcome the divorce between 

 school and home life, which is nowadays a serious defect 

 of education. Nature-study justifies its place in the curri- 

 culum only when it brings the pupils into direct contact 

 with natural objects and phenomena, and develops in their 

 minds habits of correct observation and intelligent dis- 

 crimination. The guidance provided in the memorandum 

 is practical, and preeminently designed to assist teachers, 

 so that the pupils may derive from these lessons the 

 advantages the study can ensure when rightly pursued. 

 School gardens, e.xcursions, collections, calendars, weather 

 observations, and the care of animals, are some of the 

 subjects selected for treatment, and the teachers who work 

 in the spirit of the hints and suggestions which enrich 

 these pages will have no reason to fear failure to develop 

 in their pupils open-eyed interest in nature. An appendix 

 by Prof. J. -Arthur Thomson show's teachers in detail how 

 the subject may be studied seasonally, and the difficulty 

 of obtaining material obviated. The second section of ihe 

 memorandum explains how the work in nature-study should 

 develop later in the curriculum into a more formal study 

 of experimental science, with the object of encouraging 

 the habit and spirit of accurate investigation. Individual 

 work on the part of the pupil is insisted upon, and the 

 uTiportance is pointed out of truthful and clear records of 

 results. Outlines of work are put forward as indicating 

 suitable courses of study for an intermediate school 

 devoting three hours a weelc, in two equal periods, to the 

 subject, as well as for higher schools. It is satisfactory 

 to find it laid down that the value of the work will depend 

 upon its spirit and method, and upon the power of initiative 

 and self-reliance developed in the pupils, rather than upon 

 the amount of examinable knowledge acquired. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society. February zo. — " On the Osmotic Pres- 

 sure of Compressible Solutions of any Degree of Concentra- 

 tion. Part ii. Cases in which both Solvent and Solute are 

 A'olatile." By Prof. A. W. Porter. Communicated by 

 Prof. F. T. Trouton, F.R.S. 



In a former paper (see Naturk, September 5, 1007, 

 vol. Ixxvi., p. 487) the author found an exact relation 

 between vapour pressures and osmotic pressure in the usual 

 case in which the solute may be taken as involatile. The 

 case now considered is the more general one, in which 

 both solvent and solute are volatile. 



The author has considered several cases in which the 

 vapour pressure is changed, and found that in each case 

 it is only necessary to know the partial pressure of the 

 pure solvent the vapour of which is referred to in order 

 to calculate what the change in the vapour pressure 

 amounts to. The same method might presumably be 

 applied to other cases also, such as magnetisation, &c. 



March zq. — " On Vapour Pressure and Osmotic Pressure 

 of Strong Solutions." Bv Prof. H. L. Callendar. 

 F.R.S. 



_ The foundation of the vapour-pressure theorv of solu- 

 tions laid down in this paper is the assumption of a simple 

 relation between the vapour pressure and the molecular 

 constitution of the solution. That there should be a 

 simple relation of this kind appears extremeir probable 

 •when we consider that the concentration of the vapour 

 phase in the solutions here examined is very small, and 

 that such relations generally take a very simple form at 

 extreme dilution. That such a relation should serve as 

 a key to many of the phenomena occurring in solutions is 

 not surprising in view of the fact that equality of vapour 

 pressure is one of the most general conditions of equil- 

 ibrium in physical chemistry. The relation of this 

 assumption to the gas-pressure theory, or the hydrate 

 theory, or the capillary pressure theory, as already in- 

 dicated, is that it involves them all, since they may be 

 regarded as merely different aspects of the same pheno- 

 mena. .An equivalent assumption may be formulated, at 

 least approximately, in terms of partial pressure, or 

 capillary pressure, or chemical attraction, but it would 



merely be putting the same thing in different words. The 

 vapour-pressure method appears to be the most direct line 

 of attacking the problem. If, for instance, we regard the 

 changes of capillary pressure in relation to vapour pressure 

 as defined by the relation lJdP = ~jdp, we should arrive at 

 nearly the same result by similar approximations. But 

 this method does not appear to be so convenient, because 

 it involves the volume U, which is generally unknown 

 and variable in an uncertain manner, whereas the volume 

 of the vapour v at low pressures may be regarded as con- 

 forming very closely with the laws of gases. 



There is no doubt that further experimental work may 

 be required to establish the vapour-pressure theory 

 generally, since accurate data for strong solutions are com- 

 paratively scarce. The interpretation of the ionisation 

 factor, and its relation to the heat of dilution, requires 

 further elucidation. Analysis of nearly all the data at 

 present available, in addition to the examples above cited, 

 fails to show any serious disagreement with the vapour- 

 pressure theory. The theory cannot pretend to be exact 

 for all ranges of temperature and concentration, but (it 

 seems likely to serve, at least as a second approximation, 

 for coordinating results which have hitherto appeared dis- 

 cordant. 



March 26. — " Comparison of the Board of Trade .Ampere- 

 standard Balance with the Ayrton-Jones Current Weigher ; 

 with an Appendix on the Electromotive Force of Standard 

 Cells." By T. Mather, F.R.S., and F. E. Smith. 



The paper describes experiments by which the relation 

 between the Board of Trade ampere and one-tenth C.G.S. 

 unit of current, as realised by the Ayrton-Jones instru- 

 ment (.'\yrton, Mather, and Smith, Phil. Trans., A, vol. 

 ccvii., p. 463), was determined. 



The comparison was carried out by aid of a combina- 

 tion of standard cells and resistances used as a secondary 

 standard of current. This combination was evaluated by 

 the .Ayrton-Jones current weigher at the National Physical 

 Laboratory on each of the three days during which experi- 

 ments were made at the Board of Trade Laboratory, so 

 that if any change occurred in the secondary standard it 

 would be detected. 



Two methods of comparison were employed, both giving 

 concordant results, viz. one Ayrton-Jones ampere = 100035 

 Board of Trade ampere, the latter ampere being, therefore, 

 smaller than the former by about 1/30 per cent. 



A difference of this order was anticipated, for a recent 

 determination of the electrochemical equivalent of silver 

 (Smith, Mather, and Lowry, Phil. Trans., A, vol. ccvii., 

 p. 57q) by the Ayrton-Jones instrument gave 1-11827 milli- 

 grams per coulomb, whereas tlie Board of Trade balance 

 was adjusted to correspond with 1-118 milligrams. 



According to these experiments, tlie Board of Trade 

 ampere will deposit silver at the rate of i-ii7q milligrams 

 per second, so that the Board of Trade ampere is equal 

 I0 the international ampere, as defined by silver deposit, to 

 within i/ioo per cent. 



The above experiments, combined "with figures given bv 

 Prof. Ayrton and the authors (Phil. Trans.,, A, ccvii., p. 

 i;36), enable the E.M.F.'s of standard cells to be expressed 

 in terms of the Board of Trade volt, this being defined 

 as the P.D. between the terminals of a resistance of one 

 Board of Trade ohm when one Board of Trade ampere 

 is passing. The results are : — 



E.M.F. of normal Westnn cadmium cell =1 '01869 



Board of Trade volts at 20' C. 



E. M. F. of normal Clark cell - i '4330 



Board of Trade volts at 15° C. 



The Reichsanstalt value for the cadmium cell is 1-0186 

 at 20° C, and that for the Clark cell, determined directly 

 by .Mr. Trotter. 1-4329 at 15" C. 



April 30. — " On .Scandium." Bv Sir William Crookes, 

 F.R.S. 



Scandia is one of the rarest and least known of the 

 recognised rare earths. It was discovered in 1879 by 

 Nilson, who separated it, together with ytterbia, from 

 erbia extracted from euxenite and gadolinite. Later in 

 the same year Cleve extracted scandia from gadolinite. 

 yttrotitanite, and I<eilhauite, and described the scandium 

 sulphate, double sulphates, nitrate, oxalate, double oxalates. 



NO. 2013, VOL. 78] 



