Law of Density -Numbers. 27 



Connection between the different Values of the Constant — . 



a 



In an homologous series one observes generally certain 

 properties common to all the members ; e. g.: — 



(1) A regular increase in the boiling-points of the succes- 

 sive members of the same series. 



(2) The amount of this increase varies slightly, but is from 

 16° to 20° for every addition of the group CH 2 . It was for- 

 merly supposed that the differences were equal ; but, so far 

 as experiment has gone, we are able to point to only approxi- 

 mate equality. 



In order to apply the law of density-numbers to homologous 

 series, it will be convenient to number the members of a series 

 1, 2, 3, 8[G.) according to the place in the series occupied by 

 each. I shall call these numbers m : thus benzol has m = 4; 

 it is therefore the fourth member of its series according to the 

 new Law, though at present the first one known*. 



Table XI. contains the substances each containing fourteen 

 atoms of hydrogen ; each is the seventh member of its respec- 

 tive series, for m here equals 7. Such substances I shall call 

 " corresponding " compounds. They have, as a rule, similar 

 properties, and have frequently the same constants Tn/a. 



1 may now sum up the results of observations on the con- 



Tn 



stants — as follows : — 

 a 



(1) These constants, of which we have already met two 

 (62*2 and 73*6), form an algebraic series of numbers which 

 are the same for all bodies, whether metals or non-metals, and 

 their compounds. 



(2) In an homologous series the constants increase with the 

 successive additions of CH 2 , i. e. with the value of m. 



(3) There are numerous homologous series the correspond- 

 ing members of which possess the same constant, e. g. : — 



a. Ethers . . O w H 2w 2? 



8- v • • 



^n J^2w-2 ^4- 



7- '•■ M 



^n H2W+2 O. 



8. Benzol &c. 



C n H 2rt _6. 



* M. Groshans has not made it quite clear how he obtains the num- 

 bers m otherwise than by experiment. They are found in compounds of 

 carbon, hydrogen, and oxygen by dividing the carbon and hydrogen by 

 the group CH 2 and adding one to the number thus obtained ; the residue 

 left, after deducting all the CH 2 groups, being the Jirst body : thus ether, 

 C t H 10 O, is the fifth, for it = 4(CH 2 ) + H 2 0, and H 2 is the first of the 

 series O w H2n+2 0. — Translator. 



