30 On the Law of Density- Numbers. 



(1) The Ethers C n H 2M+2 0, beginning with C 3 H 8 0, where 

 x is equal to m = 4, the differences are: — 



27-6, 26-3, 24-5, 22-8, 21*3, 20-5, 19-5. 



(2) The series beginning with Methyl Benzoate, C 8 H 8 2 , 

 where x =.m = 5, 



16-7, 16% 15-8, 15-4, 15-0. 



(3) The Alcohol series C„H 2w+2 0, beginning with CH 4 0, 

 where x = m + 3 = 5, 



16-6, 19-6, 202, 19-8, 19-4, 18-6, 17-9. 



The first three substances in Table XIV. do not exist, and 

 it is very commonly found that the first members of homo- 

 logous series, those corresponding to m=(l), (2), (3), are 

 wanting. There are, however, cases where similar bodies are 

 to be met with : thus the series C„ H 2n+2 gives rise by sub- 

 stitution to C w H 2w+1 Cl and C w H 2w Cl 2 . And all the corre- 

 sponding members of the three series possess the same 

 constants : Tn/a (or TB/a) and Ysnja (or VsB/a). 



The first members of the substituted series are chlorine and 

 hydrochloric acid, which both have ,#=1*. 



As a general rule, the value of x is a whole number, but it 

 sometimes happens that this is not the case. Thus, x = 3^ for 

 acetic acid, C 2 H 4 2 ; acetic anhydride, C 4 H 6 3 ; and a 

 similar substance differing from the anhydride in possessing 

 one atom of oxygen more, C 4 H 6 4 , methyl oxalate. All the 

 three are well known to behave anomalously. Thus the 

 vapour-density of acetic acid is abnormal. All three are solid 

 at temperatures below which their higher homologues are still 

 liquid ; and, finally, the aqueous solution of acetic acid is 

 remarkable for possessing a maximum of density at 80 per 

 cent. 



[To be continued.] 



* With regard to gases such as oxygen, and some others such as CO, 

 C0 2 , S0. 2 , CS 2 , &c, we find that the value of x is a fraction much less 

 than unity. 



Just as experiment has shown that there are cases to which the laws 

 of Avogadro and those analc gous to it are not applicable, so we find 

 similar cases in which the law of density-numbers no longer holds good. 



