160 



THE MODERN TIIEOKY OF CHEMICAL TYPES, 



So closely do clicm'cal compounds conform to this law that it is uped daily 

 to control vapor density determinations ; the experiments show whetlier the 

 condensation is to 1, 2, or 4 volumes, and whether, accordingly, the equiva- 

 lent of the body is to be divided by 7.22, 14.44, or 28.88, to calculate the den- 

 sity of its vapor. The calculation is more accurate than the actual experiment 

 on account of the superior accuracy by which the equivalents have been deter- 

 mined. The law of even atoms, and the observation that in most organic com- 

 pounds the condensation is to 4 volumes, serve often to determine the formulae 

 of organic compounds. Thus, to acetone was formerly assigned the formula 

 C3 II3 0. which salisiics neither law; by doubling its formula (and there is 

 no chemical reason to the contrary) it becomes Co Hy O2, which satisfies both laws. 

 For the same reason the formula of ether ( C4 II 5 O) may be doubled to Cs IIio O2. 



A"-ain : it has been doubted from its origin and chemical behavior whether 

 amyie obtained from amy lie alcohol (Cio Ui> (h) should have the formula Cm 

 Hii, or C20 II-.'2 ; but the latter formula agrees with the law of even atoms, and 

 with a condensation to four volumes. 



3. T/iC law of homologous scries. — Another law influencing strongly the de- 

 termination of chemical formulae, and which is one of the most remarkable 

 among the discoveries of modern chemistry, is that of homologous series. 



The following is an example : 



Sr.iMKS (C„ II„x2-) 



Etbylo butyle 

 Ethyle amyle 



Butyle 



Butyle amyle 

 Aniylo 



Boiling point. 



C,2 Hx4- 

 C14 Hi6- 



f C4 H. _ 



I C« H, \ — 

 <s C4 H5 }_ 

 \ C,„H„ ^- 



S ^8 H9 \ p TT 



J Cs H9 ^-CioHis 



{ Cs Ho \ .pi TT 



j C.oHn^-^'^^^" 



5 ClO Hll ? p TT 



02° C. 



108° 

 132^ 

 158° 



Sp. gr. at 

 00 U. 



0.701 

 0.707 

 0. 710 

 0.725 

 0.741 



Sp. gr. of 

 vapor. 



2.97 

 3.4G 

 3.94 

 4.42 

 4.91 



The membci's of this series are subject to the "same law ;'^ they advance 

 from the lowest by an increment of C2 Il2- A general formula for the scries 

 Avould be C„ H(„4. 2,) n being an even whole number. Their boiling points 

 as well as their spccilic gravities in the liquid and in the vaporous condition 

 rise gradually. We haA'e, from its position in this series, an additional reason 

 why amyle should have the formula C20 II22. and not do Hu, Indeed, as may 

 be seen in the table, amyle is regarded as having (in combination) do IIu> but, 

 when in the free state, two of its atoms arc joined together to form a compound 

 atom C2r Il2c- The following are additional illustrations of homology 



I. IIVDHOrAnRONS. 



(c„n,.) 



Ethylene d H4 



Propylene Cc He 



Butylenc Cg Us 



Amylene Cjo liio 



Olecne C12 II 12 



II. ACIDN. 



Cu Hu O4. 



Formic C2 H2 O4 



Acetic C4 H4 O4 



I'ropionic Co Hg O4 



Butyric vOy Ilg O4 



Valerianic •. . . Ctoliio04 



Palmitic C32 II32 O4 



Stearic Cac H36 O4 



