Physical Properties of analogous Organic Compounds. 193 



128° C. higher than those of the acetates; the boiling points of 

 the acetates 18° higher than those of the corresponding for- 

 mates, &c. 



The accurate study of the physical properties of all the 

 compounds of one bodyand of any single compound of another, 

 enables us to form a conclusion with respect to all other com- 

 pounds of the latter, and affords a control for the observations 

 in general. 



A similar regularity occurs in the physical properties in 

 such cases where substitutions occur. Many organic com- 

 pounds may be so arranged in a series that the amount of 

 hydrogen decreases successively, while that of chlorine in- 

 creases, which is explained by the supposition of the substitu- 

 tion of chlorine in the place of hydrogen. Let A represent, 

 for instance, a combination of oxygen and carbon which re- 

 mains unaltered, « hydrogen, /3 chlorine, m, n, x, y num- 

 bers, we then have the following scheme : — 



A + TK « V n^ 



A + (w— or) a +(n + jr)/3 



A + {m—y) a + (w+j/) /3. 



The number of atoms a and /3 taken together remains the 

 same in each compound. 



Compounds belonging to such a group or scheme may be 

 arranged in the table given at the commencement of this 

 paper, and the laws which have there been communicated may 

 also be applied to them. But we may also consider indepen- 

 dently a whole series of such compounds where chlorine and 

 hydrogen replace each other, and prove specially for them a 

 peculiar regularity in their physical properties. 



With reference to the specific volumes of such compounds, 

 the following law holds good : — 



" If in any compound x atoms of hydrogen are replaced 

 by {x atoms of chlorine), the specific volume of the new com- 

 pound is greater than that of the former by the number x. 80." 



[The number 80 is merely approximate, inasmuch as no 

 attention has been paid to the temperature at which the spe- 

 cific volumes should be considered.] 



In proof of this law I will arrange together a large number 

 of substitutions, and always calculate by the above law from 

 the observed density of the preceding compound the density 

 of that which lias been formed from it by substitution, and 

 compare the calculations vvith the observations. 



Phil. Mag. S. 3. Vol. '20. No. 130. March 184.2. O 



