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 of the 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 52.11 per cent, carbon, 13.04 per cent, hydrogen, 

 and 34.78 per cent, oxygen. The Irypothesis 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 tetravalent. 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 TT[C.'TT we can produce from it (see above) the hydro- 



-ti* *-U} 



HH 

 carbon H.C.C.H = C 2 H 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 



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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.H, 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.C1 + K.O.H = H.C.C.OH + KC1. 



HH HH 



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

 bination with K, has changed places with 01. The result- 

 ing compound, C 2 H 5 (OH), is ordinary alcohol, and we 



