CONSTITUTION OF CHEMICAL COMPOUNDS. XXXI 



A simple example may suffice to illustrate the rationale of 

 the process. Let us take ordinary alcohol. We can first 

 establish the formula by means of analysis and the deter 

 mination ofthe specific gravity of its vapor. This we 

 find to be C 2 H 6 0. This formula is the expression of a fact 

 and a hypothesis. The fact expressed is that alcohol con 

 sists of 52.17 per cent, carbon, 13.04 per cent, hydrogen, 

 and 34.78 per cent, oxygen. The hypothesis of which it is 

 an expression is that the molecules of all chemical com 

 pounds in the form of vapor have the same volume as a 

 molecule of hydrogen. This hypothesis, when applied, 

 tells us the weights of the atoms contained in the mole 

 cule of alcohol and the weight of the molecule of alcohol, 

 and hence, further, the number of atoms of carbon, hydro 

 gen, and oxygen contained in the molecule under considera 

 tion. We know that hydrogen is monovalent, oxygen biva 

 lent, and carbon tetravalcnt. It now remains to decide 

 how those atoms are united what the constitution of 

 alcohol is? If we take marsh gas, CH 4 , which, according 

 to our ideas, as we have seen, can only have the constitu- 



TT TT 



tion jjiC. jj we can produce from it (see above) the hydro- 



HH 

 carbon H.C.C.H = C 2 II 6 ; if we now replace one of the 



HH 



hydrogen-atoms of this compound by chlorine, we have 

 HH 



the compound H.C.C.C1 = C 2 H 5 C1, and experience shows 



HH 



us that only one compound of this composition can re 

 sult, it being immaterial which one of the hydrogen- 

 atoms is replaced. If we, further, allow the substance 

 K.O.II, in regard to the constitution of which, according 

 to the principles already laid down, there can be no ques 

 tion, to act upon this compound, two products are formed, 

 thus : 



HH HH 



H.C.C.Cl + K.O.II = H.C.C.OH + KC1. 



HH HH 



The water-residue, the hydroxyl group, before in com 

 bination with K, has changed places with Cl. The result 

 ing compound, C 2 IP(OH), is ordinary alcohol, and we 



