PROCEEDINGS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. clxxi 
In no department of Chemistry has greater advance been made 
than in the study of the organic compounds, a result which has been 
of immense importance in the sister science of Biology. In this 
department the chief honour is due to Baron Liebeg, whose work 
extended over the first half of the reign. The practical outcome 
of his labours, and of the labours of other workers in the same 
field, is seen not only in the revolution which has taken place 
in pathology and physiology, but in the new methods of scientific 
x 4 griculture. 
Perhaps the most important chemical law formulated during the 
reign is the Periodic Law of the Elements, which was established in 
1869. On the principle of this Law, Mendelejeff drew up his “Table 
of the Elements,” and predicted that certain gaps which occurred in 
the series would be filled up by the discovery of new elements. In 
1872 he predicted that two such elements would be discovered, the 
one below Aluminium and the other below Boron. The former he 
called, in anticipation, “Eka-Aluminium,” and the other “Eka-Boron.” 
In 1876 the first of these was discovered by Boisbaudran, and in 1879 
the second was brought to light by Nilson, and they are now known 
as Gallium and Scandium respectively. The remarkable thing is 
that the predictions of Mendelejeff in regard to the properties of 
these undiscovered elements were in every case verified by their 
discoverers. 
As indicating the progress which has been made in chemistry 
during recent years, it may be mentioned that the total number of 
elements known in 1897 was seventy-seven,* as compared with forty- 
six f in 1837. Of the thirty-one which have been added to the list 
during the reign, perhaps the most interesting are Argon and 
Helium. The former, which was discovered in 1894 by Lord 
Rayleigh and Prof. Ramsay, constitutes about one per cent, of 
atmospheric air; while the latter, which was discovered in 1895 by 
Prof. Ramsay, affords a striking example of the reliability of spectro¬ 
scopic methods, having been first detected in the spectrum of the 
Sun, and then found in the mineral Cleveite. 
As regards the more theoretical side of the science, speculation, 
as in all other sciences, has been busy during the last quarter of a 
century. In particular, much has been said regarding the ultimate 
constitution of matter, and although nothing definite has been 
proved, yet questions have been raised and theories suggested which 
may lead to important results in the near future. For instance, are 
the so-called “ elements ” really simple substances, or are they 
capable of further simplification ? Does matter exist in three forms 
only, or is there an ultra-gaseous form ? Have the elements always 
been distinct from each other, or have they all arisen from some 
antecedent form of matter? This last question, which has been 
raised by Crookes, one of the profoundest physicists of our time, 
shows how powerfully the idea of evolution has permeated chemistry, 
in common with every other science, during the last few decades. 
* W. A. Tilden’s “Manual of Chemistry,” pub. February, 1S97. 
+ Haydn’s “ Dictionary of Dates.” 
