234 Intelligence and Miscellaneous Articles. 
by the sun in 4 seconds with a lens 43 inches focus and a little less 
than } inch diaphragm ; or with a compound lens having an aperture 
of one inch, and the same focal length, in a quarter of a second. 
« Researches on the Reproductive Organs of the Aunelids.” By 
Thomas Williams, M.D., F.L.S. 
« Addition to a Memoir on the Determination of Unknown Func- 
tions that are evolved under Definite Integrals.” By J. Gomes de 
Souza, Esq. 
In his previous communication (Phil. Mag., March 1857) the 
author developed ¢z in terms of the function A,e™,". In the present 
communication he developes in a more general way, using terms of 
the form A, |*etar(wym,)dw, the function of @ being assumed at 
pleasure. 
XXVIII. Intelligence and Miscellaneous Articles. 
ON THE CALCULATION OF VAPOUR DENSITIES. 
BY HERMANN KOPP. 
HEN the atomic weight of a substance is calculated for oxygen 
=8, and its vapour density for atmospheric air =1, sup- 
posing these data to be rigidly correct, it is found that the quotient 
of the atomic weight by the density is equal to one of the following 
numbers :— 
28°88 14°44 7°22. 
The number 28°88 corresponds with a condensation to 4 volumes. 
”? 14°44 2? ” .? 2 ” 
” 7°22 > 3? ”? 1 ” 
These numbers represent what may be called the normal quotients. 
When the density of the vapour of a substance has been approxi- 
matively determined, the quotient of the atomic weight by this den- 
sity is a number very near one of these normal quotients. This 
operation immediately indicates the mode of condensation of the 
vapour. On the other hand, it is always easy to calculate the theo- 
retical density of a vapour of a substance by dividing its atomic 
weight by one or other of the normal quotients. ‘Thus, for the 
immense majority, if not the whole, of the organic compounds, the 
theoretical vapour density is found by dividing the atomic weight by 
the number 28°88. 
Some examples will show the exactitude and the advantages of 
this mode of calculation. When the atomic weight of acetic ether, 
C8 Hs O+=88, is divided by the vapour density, which experiment 
gives for this substance = 3°112, the quotient is equal to 
8 
37112 
28°2, a number very near 28°88. This result indicates a condensa- 
tion to four volumes. The theoretical vapour density of acetic 
zether is therefore =3°047. 
88 
28°88 
a 
