SCIEj^TIFIC culture. 593 



molecules of the factors are written on one side and the symbols of 

 the molecules of the products are written on the other side of an equa- 

 tion, the number of molecules of each substance involved being indi- 

 cated by numerical coefficients. 



The atomic symbols, as we have seen, stand for definite weights. 

 In the same way, the molecular symbols stand for definite weights, 

 which are the sums of the weights of the atoms of which each consists, 

 and in every chemical equation the weights of the molecules repre- 

 sented on one side must necessarily equal the weights of the molecules 

 represented on the other. The chemical process consists merely in the 

 breaking up of certain molecules, and the rearrangement of the same 

 constituent atoms to form new molecules. Again, as the molecular 

 symbols represent definite weights, the equation also indicates that a 

 definite proportion by weight is preserved between the several factors 

 and products of the process represented. 



Again, since every molecular symbol represents the same volume 

 when the substance is in an aeriform condition, it follows that the 

 relative gas volumes are proportional to the number of molecules of 

 the aeriform substances involved in the reaction. Thus it is that these 

 chemical equations or reactions are a constant declaration of the three 

 great fundamental laws of chemistry. 



In order to enforce the above principles, a great number of exam- 

 ples should now be given which should be so selected as to illustrate 

 familiar and important chemical processes, including the all-important 

 phenomena of combustion. In each case, the student, having made 

 the experiment, should write the equation or reaction which represents 

 the process, and should be made to solve a sufficient number of 

 stochio-raetrical problems, involving both weights and volumes, to 

 give him a complete mastery of the subject. Such questions as these 

 will test the completeness of his knowledge : 



Why is the symbol of water HgO? What information does the 

 symbol COg give in regard to carbonic-dioxide gas ? Write the re- 

 action of hydrochloric acid on sodic carbonate, and state what infor- 

 mation the equation gives in regard to the process which it represents. 



Of course, such questions may be greatly multiplied, and I cite 

 these three only to call attention to the features of the method of 

 instruction I have been endeavoring to illustrate. 



But, besides teaching the general principles of chemical science, it 

 is important to give the student a more or less extended knowledge of 

 chemical facts and processes — especially such as play an important 

 part in daily life, or in the arts — and such knowledge can readily be 

 given in this connection. Beyond this I do not deem it desirable to 

 go in an elementary course of instruction. The way, however, is now 

 opened to the most advanced fields of the science. A comparison of 

 symbols and reactions leads at once to the doctrine of quantivalence, 

 and to the results of modern structural chemistry, which this doctrine 



VOL. XXT. — 38 



