INDUSTRIAL PROGRESS DURING THE YEAR 1872. xxv 



Avogadro, Ampere, Konig, and Clausius on the constitution 

 of perfect gases." He would " found upon this theory," there- 

 fore, " the demonstration of the limits of the divisibility of 

 elementary bodies ; that is to say, the existence of elementa- 

 ry atoms." With his own students, Cannizzaro starts with 

 proclaiming the invariability of the material mass in chemi- 

 cal changes, pointing out " that the only constant property 

 of matter is its ponderability." He then passes to the Dalto- 

 nian theory, establishes the correctness of the atomic weights 

 by the Gay-Lussacian law of combining volumes, and easily 

 demonstrates the molecular condition of simple matter. He 

 thus places the fundamental notions of atoms and molecules 

 upon a solid basis, freed from every thing not necessarily 

 connected with them. Then it is that the instructor is in " a 

 position to attack the difficulties encountered in the applica- 

 tions of these notions to particular cases." The assistance 

 of specific heat, of isomorphism, and of chemical analogy in 

 fixing the size of molecules, and the true meaning and value 

 of the theory of atomicity, may then be taught, the student 

 being made to recognize the dynamic as well as the ponder- 

 able phenomena of chemical change. 



The researches of Berthollet, of Thomson, and of Favre in 

 Thermo-chemistry during 1872 are most promising. While it 

 can not be doubted that the dynamic equation of a given re- 

 action would be fully as valuable as the chemical equation 

 of the same reaction, the dynamics of chemical changes have 

 only just begun to be studied. If, for example, the amount 

 of heat given off by the union of each of two bases with one 

 given acid be known, and the heat in the case of the union 

 of these bases with a second given acid be also known, then 

 it is evident that any double decomposition occurring upon 

 the mixture of these salts must be accompanied by a thermal 

 disturbance proportional to the difference given in the two 

 cases. Hence the fact and direction of chemical decomposi- 

 tion may be solved dynamically, & priori. It is by methods 

 of this sort that Berthollet has established the previously 

 received assumption that it is the most powerful base in ev- 

 ery case which unites with the strongest acid. Thus, if zinc 

 acetate and sodium sulphate be mixed in solution, there is no 

 exchange ; but if zinc sulphate and sodium acetate be mixed, 

 the production of heat proves that an exchange takes place. 



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