602 REPORT— 1897. 



volatilisatiou before the blow-pipe, for the effect of environing vapors on the changes 

 soon attract attention. 



Chemistry is rapidly becoming a branch of physics. Physical methods and 

 values may well be used, with this difference, that while in physics we deal with 

 sensible volumes and molar masses, in chemistry we deal with atomic masses and 

 volumes. It is very easy to pass from one to the other, as in atomic volume, 

 atomic heat, and similar values. 



When some atomic volumes have been computed and graphically illustrated as 

 in Table II., which was exhibited at the meeting, at once the students will be 

 ready to make certain deductions which future experiment will put to the test. 

 Those elements which exhibit large atomic volumes may be expected to be com- 

 paratively soft, light, fusible, volatile, soluble, poor conductors of heat and electricity, 

 chemically intense, exhibiting a constant valency, and are found to readily decom- 

 pose water, liberating either or H. Their compounds will be hard to reduce, 

 show great heats of formation, are white or light-coloured, easily soluble, and of 

 few types, e.g., Na, K, 01, Br, O, S, Ca, Sr, Ba. The elements which exhibit 

 small atomic volume will be the opposites in every particular ; for example, C'u, 

 Ag, Pb, Mn, Or, Fe, Ni, Co, &c. Table II. shows the effect of greater or smaller 

 attraction between like atoms. So much of chemical knowledge may be based on 

 the physical computations of specific gravity, united with the chemical idea of 

 reacting masses. The periodic variation of atomic volume should then be exhibited, 

 and the resulting chemical properties tested in the laboratory work. To prove or 

 disprove a theory or a law is as valuable an exercise in research methods as the 

 discovery of new truth. It has the advantage of giving some direction to the 

 student's search. 



We have in these physical values an explanation for the division of each family 

 into two groups, which, along with family likenesses, exhibit marked differences, 

 as Cu, Ag, and Au in Family I., and Zd, Cd, and Hg in Family II. The chemical 

 relations of the members of any family to each other may be illustrated by two 

 lines, coalescent at the top, but separating as we descend to the elements of greater 

 atomic mass. 



Dulong and Petit's law may be used for the computation of some atomic 

 masses, for if we have a few blocks of different metals, of masses in grams pro- 

 portional to their reacting masses, it can easily be found by experiment with small 

 calorimeters that they all have the same capacity for heat, and the value 6-4 has a 

 definite meaning, as the number of small calors or therms required to heat such 

 masses 1 degree. The idea of atomic heat becomes easily so clear and definite that 

 it may be tested in the laboratory and used in atomic mass determinations. 



The most striking physical property used in chemistry is that of colour. The 

 hint of any colour law at once awakens the spirit of research. It is easy so to 

 grade experiments that the class readily make their own deductions. Carnelley's 

 law may be stated in this form. Given the following chromatic scale, 



White, colourless, violet ; 

 Indigo, blue, green ; 

 Yellow, orange, red ; 

 Brown and black : then 

 Atomic Mass, Temperature, and Valency 



Depth of shade 



Atomic Volume, and Hydration 



The reactions on gypsum tablets give many examples of this. 



The general condition is that condensation of matter tends to move the shades 

 toward the less refrangible end of the spectrum from white to black. Hydration 

 generally has the effect of dilution, and rise of temperature the same effect as con- 

 centration, as Ostwald has shown to be the case in aqueous solutions, and as is 

 found to be the case in solutions in borax and metaphosphoric acid. 



The question of valency is one troublesome to the student, chiefly on account of 

 the variation among the elements and variations in the behaviour of the one 

 element. This may be reduced to order, and variations in valency are seen to be 



