ON TEACniNG CIIEJIISTRT. 249 



Si'AOE VI. — Sludies of the physical properties of gases in comparison with 

 those of liquids and solids. The violecidar and atomic theories and 

 their application. 



A series of quantitative experiments on the effect of heat on solids, 

 liquids and gases should now be made, and these should be followed 

 by similar experiments on the efiect of pressure ; the similar 

 behaviour of gases, and the dissimilar behaviour of liquids and 

 solids, is thus made clear. The condensation of gases is then demon- 

 strated and explained, and also tho conversion of solids and liquids into 

 gases, and the dependence of boiling-point on pressure and temperature. 

 Kegnault's method of determining gaseous densities is studied, and the 

 method of determining vapour densities is illustrated. The molecular 

 constitution of a gas is now discussed ; the phenomena of gaseous and 

 liquid diffusion are studied and a brief reference is made to the kinetic 

 theory of gases ; then Avogadro's theorem is expounded and applied to 

 the determination of molecular weights ; and eventually the atomic 

 theory is explained, and the manner in which atomic weights are 

 ascertained is brought home to the pupils. The use of symbols must then 

 be taught. Finally, the classification of the elements in accordance with 

 the periodic law should be explained. 



It is all-important that at least a large proportion of the experiments 

 in each of the stages should be made by the pupils ; but even if this were 

 not done and the lessons took the form of demonstrations, much valuable 

 instruction might still be given. 



The majority of pupils probably would not proceed to the fifth and 

 sixth stages ; but those who pei-force must terminate their studies with- 

 out gaining any knowledge of chemical philosophy should unfailingly be led 

 to make a few simple quantitative experiments : for example, to determine 

 silver volumetrically, and the method of determining the composition 

 of water and chalk gas should be demonstrated in their presence : and it 

 may be added that if only the examples in Stages I. and II. and Problems 

 I. to V. of Stage III. were thoroughly worked out, most important educa- 

 tional training would be given and much valuable information as to the 

 nature of common phenomena would be gained. 



The complete course would undoubtedly take up considerable time, but 

 so does a satisfactory mathematical or classical course of study, and it is 

 absurd to suppose that useful training in science is to be imparted in a few 

 months. If instruction be given in the manner suggested at all generally, 

 it will be necessary, however, to modify the present system of testing results. 

 Pupils could not be expected to pass at an early age examinations such as 

 are at present held, and awards would have to be based chiefly on an 

 inspection of the classes at work and of note-books and on viva-voce 

 ([uestioning. But all are agreed that the present system of payment on 

 results tested by a terminal examination is a most unhealthy one, and 

 that a more rational system must be substituted for it. I may suggest 

 that if members of the staff of science colleges, such as are now 

 established in so many towns, could be appointed supei-vising inspectors, 

 ■whose duty it would be to advise teachers in schools and occasionallij to 

 inspect the teaching in company with the permanent inspector, it would 

 be possible to secure the assistance of a body of men who are in touch 

 with scientific progress and conversant with the improvements which are 

 being effected. A man who ' once an inspector is always an inspector ' 

 of necessity must get into a rut, and will escape from the wholesome 



