26 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[July 13, 1872. 
tides clears them of their black coating. They are then 
hung up to dry and bleach in the sun. 
The export duty levied on sponges is los. 9d. the 
•cwt.; hut the Custom-house returns do not afford a 
proper index of the quantities exyorted yearly, as nearly 
the whole of the sponges fished by the Greeks are not 
landed, hut shipped direct from the depots, on hoard 
•each of which, however, there is a representative of the 
sponge farmer, to withdraw or dispose ot the share due 
to him. 
From the information I have been able to gather, it 
appears that the produce of this fishery is susceptible of 
considerable augmentation, by an increase in the num¬ 
ber of fishermen; and, it is stated that, a new sponge 
is reproduced within a year wherever one has been 
removed. 
THE CHEMISTRY OF THE HYDROCARBONS. * 
BY C. SCHORLEMMER, F.R.S. 
{Continued from page 5.) 
Paraffins. —Kekule first pointed out that when two 
atoms of carbon combine, the most simple, and therefore 
the most probable case, is that one combining unit of 
one atom enters into combination with one combining 
unit of the other atom. The group C 2 thus formed is 
consequently a hexad. When more than two atoms of 
carbon are linked together, they may combine in a simi¬ 
lar manner, one-fourth of the combining capacity of one 
atom being saturated by one-fourth of the combining 
capacity of another. By saturating the free combining 
capacities of such a group with hydrogen, we obtain a 
scries of hydrocarbons, having the general formula 
C n H 2tl * 2 , to which the name paraffins has been given. 
This name was originally applied to the solid members 
of the series, on account of their chemical indifference; 
but, as the gaseous and liquid members exhibit the same 
character, it appears convenient, as H. Watts has sug¬ 
gested, to apply the term paraffin as a generic term for 
the whole series. 
The most characteristic property of the paraffins is 
that they are not capable of uniting with any other 
bodies, and for this reason thev have also been called 
saturated hydrocarbons. 
We are at present acquainted with a considerable 
number of paraffins, amongst which there are found 
many isomerides. To explain the isomerism in this 
series two assumptions have been made. 
One, which found many advocates up to the year 1864, 
was that the four combining units of the carbon atom 
have not the same value or the same function. This 
assumption was made in order to explain the existence 
of two isomeric hydrocarbons having the formula C 2 H 6 , 
it being believed at that time that methyl gas was dif¬ 
ferent from ethelhydride. But Crum-Brown has shown 
that there is a certain degree of inconsistency in this 
hypothesis (Trans. Roy. Soc. Edin. xxiii. 707). Butlerow, 
in endeavouring to explain the isomerism of these two 
hydrocarbons, argued that in methyl gas the two atoms 
of carbon were combined by two combining units of the 
same kind (which he called secondary affinities), each 
being the combining unit which in methyl iodide is 
saturated with iodine. In hydride of ethyl the carbon 
atoms are united in the same way as in other ethyl com¬ 
pounds, and therefore probably as in the acetal com¬ 
pounds, one of which is acetonitrile or methyl cyanide ; 
the one is therefore the combining unit of methyl, and 
the other that of cyanogen. These must be different, 
because the two hydrocarbons are not identical. To in¬ 
dicate this, Butlerow calls the free combining unit of 
* A lecture delivered before the Chemical Society, April 
4th, 1872. Reprinted from the ‘Journal of the Chemical 
Society ’ for Jime, 1872., 
cyanogen a primary affinity. We have thus in methyl 
gas two secondary affinities united together, and in 
hydride of ethyl a primary united to a secondary. 
“ But by carrying this argument a little further, we 
arrive,” says Crum-Brown, “ at an absurdity; thus the 
carbon radical of acetic acid is the same as that of oxy- 
acetic acid, and that again is the same as the carbon 
radical of oxalic acid, and therefore as that of oxalic- 
nitrile or cyanogen gas. In cyanogen gas, however, we 
have the two carbon atoms united by two primary 
affinities; but we have before proved that in the acetic- 
acid series they are united by a primary affinity of the 
one to a secondary of the other. It is obvious, then, 
that at least one of our assumptions is false.” . 
About the same time I proved by experiment that 
methyl gas or dimethyl is identical with ethyl hydride; 
and since that time a few chemists only have made use 
of the above hypothesis in order to explain certain cases 
of isomerism. 
If the four combining units of the carbon atom have 
the same value, isomerism in the paraffin series can only 
be caused by a different grouping of the carbon atoms ; 
and in this case it is easy to find out the number of iso¬ 
merides which can exist in the case of each member of 
the homologous scries. According to this theory, the 
first three members are not susceptible of isomeric modi¬ 
fications, whilst the four-carbon paraffin, C 4 H 10 , can exist 
in two, and the five-carbon paraffin in three isomeric 
forms, etc. 
This theory is completely borne out by facts. Of the 
three lowest members, no isomeric forms are known, but 
we are acquainted with two containing four atoms of 
carbon, and with three containing five atoms. 
Some time ago I showed that all the paraffins of known 
structure may be divided into four groups :— 
1 . Those in which each carbon atom is directly com¬ 
bined with at most two carbon atoms. 
2. Those in which one carbon atom is united directly 
with three others, or which contain the group iso- 
propyl. 
3. Those containing the group isopropyl twice. 
4 . Those in which one carbon atom is combined 
directly with four others. 
Of these groups, the first, which I called normal pa¬ 
raffins, was at that time only imperfectly known. In¬ 
deed, the structure of some of the members was not 
proved at all; they were placed there only because it 
appeared for several reasons probable that they possessed 
a very simple structure. Since that time, however, I 
have increased their number, and proved that the hydro¬ 
carbons placed in this group are really normal paraffins. 
The only means we hitherto possessed for determining 
the constitution of a paraffin was either to obtain it 
from an alcohol or other compound of known structure, 
or to convert the paraffin into an alcohol, and then 
endeavour to find out the constitution of the latter. 
The latter method, however, has been surrounded by 
such difficulties that it appeared almost impossible to 
make use of it. I have, however, succeeded in over¬ 
coming some of those obstacles, and been able to obtain 
much larger quantities of the alcohols than formerly', so 
that I could study' fully' their products of oxidation. An 
investigation of the paraffins contained in Pennsylvanian 
petroleum showed that they' belong to the first group, as 
the alcohols derived from them, as well as the acids ob¬ 
tained by oxidizing the latter, were found to be normal 
compounds. 
Before I take leave of the paraffins, I have to say a 
few words about the paraffins par excellence, viz., the solid 
paraffins. These bodies, which resist so energetically the 
action of chemical agents that they have obtained their 
name from this fact, appear to be very' unstable bodies 
at a high temperature, although, curiously enough, they' 
are produced by r destructive distillation. Thorpe and 
Young have shown (Proceedings of the Royal Society', 
xix. 370), that by distilling solid paraffin under pres- 
