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808 
animals, and that we could never expect to 
prepare them in the laboratory. But this 
idea soon had to be abandoned, for in 1828 
Wobler succeeded in building up urea from 
simple inorganic substances, and thus the 
first synthesis of an organic substance was 
effected. This was soon followed by that 
of acetic acid by Kolbe, and then year after 
year an ever larger and larger number of 
substances was added to the list of synthetic 
compounds. It would take too long to 
enumerate all the compounds that have 
been made artificially in the laboratory. It 
is enough to say that the hydrocarbons of 
petroleum, common alcohol, wood alcohol, 
fusel oil, the ethers, the etheral and essen- 
tial oils, the fatty acids, glycerine, grape 
sugar and fruit sugar, coloring matters and 
dye stuffs like indigo and turkey red, aro- 
matic substances like oil of bitter almonds, 
vanilline and coumarine and many others, 
have been made. 
One hundred years ago it was generally 
believed to be impossible for two substan- 
ces of entirely different properties to have 
the same composition. When Liebig in 1823 
found that Wobler had analyzed silver cy- 
anate and stated the percentage composi- 
tion, he saw that it was identical with the 
percentage composition of silver fulminate 
as found by himself. He at once wrote to 
Wohler and told him that he must have 
made a mistake. Silver cyanate and silver 
fulminate were very different substances, 
he said; they could not possibly have the 
same composition. Wohler repeated his 
analyses and found that they were correct. 
Liebig again analyzed silver fulminate and 
found that his figures also were correct. 
Both substances had the same percentage 
composition. A few years after, Berzelius 
showed that racemic and tartaric acids 
have the same composition, but different 
properties, and from this time on substan- 
ces of this kind have been called isomeric. 
This phenomenon of isomerism, so rare at 
SCIENCE. 
(N.S. Vou. XIII. No. 334. 
one time, is now very common. We have, 
for example, 55 substances having the for- 
mula C,H,,O,, all having the same elements 
in the same proportions, or the same kind 
of atoms and the same number of atoms of 
each kind. To explain isomerism it was 
necessary to assume that in these different 
bodies the atoms are differently arranged 
or grouped. Thus there came into chemis- 
try the idea of structure or constitution, 
and by this term is meant the way in which 
the atoms are united to form the smallest 
particles of compounds. By studying the 
methods of formation and of decomposition 
of compounds it has been found possible to 
draw conclusions as to which atoms are 
more closely associated with one another: 
In the year 1865 the methods of determin- 
ing the constitution of substances had been 
brought to a high state of development as 
the result of the work of Professor Kekulé 
in Bonn. Kekulé proved experimentally 
that in a compound each atom is not united 
directly with all the other atoms, but that 
certain atoms act like links in a chain and 
hold different atoms together to form defi- 
nite structures. 
The immediate effect of this theory was 
that it led to a great deal of work, the ob- 
ject of which was to determine the way in 
which the atoms are linked in different sub- 
stances. When once this structure had been 
determined, it was easy to see how the com- 
pound might be built up from simpler sub- 
stances. The outcome was that hundreds 
of substances were made synthetically, and 
in the attempt to make artificially the valu- 
able and useful substances, very often new 
ones were discovered that in turn were 
found to possess valuable properties. For 
instance, after determining the constitution 
of atropine, Ladenburg, in making it syn- 
thetically, succeeded in making several 
modified atropines, such as homoatropine, 
which also have valuable properties. Pro- 
fessor Fischer attempted to unravel the 
