August 10, 1872.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
107 
been destroyed, a complete proof that naphthalene has 
really the constitution assigned to it. 
Whilst amongst the mono-substituted benzenes, no 
isomeric forms occur, we find that the monosubstitution 
products of naphthalene can exist in two. isomeric 
modifications. This can also he easily explained from 
the constitution of this hydrocarbon. By representing 
it by two hexagons and numbering the corners, repre¬ 
senting the carbon atoms— 
10 
9 
y/\ A 
'//_ \s/ 
5* //- 
*S/ \A 
8 6 
A further proof of the correctness of this view is, that 
by fusing anthraquinone with caustic potash, benzoic 
acid is formed. 
C 14 H 8 0' 2 + 2KOH = 2C 7 H 5 KOo, 
The molecule of anthraquinone splitting up in the fol¬ 
lowing way:— 
H H 
C = C 
/ \ 
H-C C- 
c-c 
/. \ 
H C- 
0- 
H H 
C == C 
Vg'- 
/ \ 
-C H 
-0 
we find that each of the atoms 1, 3, 6, and 8, is com¬ 
bined with another atom (2 or 7) in which all the 
•combining units are saturated with carbon, whilst the 
atoms 4, 5, 9, and 10 are combined with carbon atoms 
to which hydrogen is attached. The functions of the 
atoms 1, 3, 6, and 8 will, therefore, differ from those of 
the four latter. This also explains the existence of two 
dinaphthyls, one of which has been obtained by the 
action of sodium upon monobrom-naphthalene, and the 
other by passing the vapour of naphthalene through a 
red-hot tube. 
In most kinds of coal-tar containing naphthalene 
there occurs also anthracene , C 14 Ii 10 , a body exhibiting in 
its chemical relations great resemblance to benzene and 
naphthalene. The constitution of this hydrocarbon has 
been ascertained by Graebe and Liebermann by their 
beautiful researches on alizarin (Ann. Chem. Pharm. 
Suppl., vii. 257). 
Baeyer found that by heating phenols and compounds 
allied to them with zinc-dust, they are reduced to the 
hydrocarbon from which they are derived. By making 
use of this reaction, Graebe and Liebermann found that 
alizarin was a derivative of anthracene, and. were thus 
enabled to effect for the first time the artificial pre¬ 
paration of a natural dye-stuff. 
This example shows better than any other the cor¬ 
rectness of the definition of organic chemistry.“ as the 
-chemistry of the hydrocarbons and their derivatives . 
The fact that alizarin is a derivative of anthracene 
enables us, as these chemists pointed out, to discuss the 
constitution of this hydrocarbon. From Limpricht s 
synthesis of anthracene from benzyl chloride it might be 
inferred that it is diphenyl-acetylene, C 6 H 5 .C=^ G).G 6 H 5 . 
But this formula has to be rejected, because on oxidizing 
alizarin we obtain phthalic acid ; and as further benzene, 
naphthalene, and anthracene form a series, each member 
of which contains C 4 II 2 more than the preceding, it 
Appears most probable that anthracene is built up trom 
three aromatic nuclei in the same way as naphthalene 
from two. The formation of anthracene from two mole¬ 
cules of benzyl-chloride can now be easily explained. 
Each benzene nucleus loses one atom of hydrogen, and 
each of the groups CH 2 C1 loses a molecule, of hydro¬ 
chloric acid, and the two residues C 6 H 4 .CH join together 
thus— 
H II 
H H 
H 
H 
II H 
C=C 
G=C 
C= 
=C 
c=c 
/ \ 
/ \ 
/ 
\ 
/ \ 
JIG GH 
HG CH 
HC 
c 
— C CH 
^ //,. 
\ ^ 
A 
G—G 
G—G 
G- 
-G 
G—C 
H \ 
/ H 
H 
\ 
/ H 
(HCl)HC 
CH(HCl) 
C 
n 
H 
The complete reaction which takes place by heating 
benzyl chloride with water, takes place according to the 
equation— 
4(C 6 H 5 .CH 2 C1) =C 14 H 10 + C 14 H 14 + 4HC1. 
The highest boiling portions of coal-tar contain, 
besides anthracene, two other hydrocarbons, pyrene 
G lf) H 10 , and chrysene C 18 II 12 , which have been also studied 
by’Graebe and Liebermann (Ann. Chem. Pharm., clviii. 
285 and 299). They have found that these bodies 
exhibit in their chemical properties so close an analogy 
to anthracene, that their constitution must be very 
similar to that of the latter hydrocarbon. Both yield 
quinones on oxidation, which proves that they also 
consist of closed chains of carbon atoms. According to 
Liebermann, a similar constitution is possessed by 
idrialene , C 22 H 14 , a hydrocarbon occurring in idrialite, 
a mineral found in the mercury mines of Idria (Deut. 
Chem. Ges. Ber., iii. 154). This hydrocarbon forms the 
last member of a series which are derived from benzene 
by the successive addition of C 4 H 2 — 
Benzene.C G H 6 . 
Naphthalene.GioHs- 
Anthracene. Ph^io- 
Chrysene.C. 8 H 12 . 
Idrialene.C 22 II 14 . 
Pyrene, which does not belong to these series, is 
isomeric with diacetenyl-phenyl. , C 6 H 5 .C=C—Ce=C.C 6 H-, 
a hydrocarbon discovered by Glaser, who has pointed 
out that of all known hydrocarbons it contains relatively 
the greatest amount of carbon, viz., 95 per cent., or more 
than coal or anthracite. 
I have now finished my task, and. have only to regret 
that the magnitude of the subject did not allow me to 
dwell longer on certain points, whilst others, such as. 
Berthleot’s remarkable researches on the formation ot 
hydrocarbons at a high temperature, and the transfor¬ 
mation of all carbon-compounds into hydrocarbons by 
means of hydriodic acid, could not be mentioned at all. 
But the latter investigations alone would be sufficient to 
form the subject of a separate lecture. 
There is perhaps no branch of our science which 
shows better the progress made by chemistry during the 
last thirty years, than that which I have brought before 
you to-night. And to what cause do we owe this rapid 
advance in our knowledge F I think this mainly due to 
the atomic theory, which found birth in Dalton’s 
speculative mind, and has been gradually expanded and 
developed to its present state by the efiorts of many 
eminent chemists. 
But the atomic theory is generally accepted not only 
by chemists, but also by physicists, who have thought it 
of the greatest importance to find out the nature of an 
atom itself. Sir William Thompson has lately shown 
us how to solve a problem never dreamt of by chemists, 
viz., how to ascertain the absolute weight and size of an 
I atom (‘ Nature,’ 1871, nos. 22, 31). Is.it not, therefore, 
strange that we find chemists who desire to kick from 
under them the ladder by the aid of which, in no small 
degree, so great a progress has been achieved ? 
Such attempts are, however, not only of recent, date. 
! In opposition to Dalton and Berzelius, Wollaston intro¬ 
duced the term equivalent instead of atom. But whilst 
