Henry Clifton Sorby. lxi 
in proving that there undoubtedly is a direct correlation between mechanical 
pressure and certain kinds of chemical action. The results of this important 
research formed the subject of the Bakerian lecture which he gave to the 
Royal Society in 1863. The most striking geological illustration of the truth 
of his conclusion was furnished by him from various limestone conglomerates 
which have suffered severe compression and in which the pebbles have 
indented each other, the solution of their substance being greatest at the 
points of contact where the effects of pressure were most pronounced. 
Sorby’s interest in chemical questions, which began in his youthful days 
with his tutor, continued active all through his life, and gave a special 
character to many of his geological and mineralogical papers. One of his 
early observations, for example, related to the origin of magnesian limestone 
by the alteration of an ordinary calcareous deposit. In another enquiry, 
which involved an extensive series of experiments, on the production of 
artificial pseudomorphs, by the action of cold or highly-heated solutions, he 
showed that certain rocks, like the Cleveland Ironstone, were originally 
composed of carbonate of lime, which has been replaced by carbonate of iron 
derived from the associated strata. Again, he conducted a long investigation 
into the occurrence of the two forms of carbonate of Lhme—calcite and aragonite 
—in the shells of mollusca, and he was thereby led to some interesting and 
important conclusions. He found that some shells are composed of calcite, 
some of aragonite, and others partly of the one and partly of the other in 
distinct layers. He ascertained, further, that calcite, being in a state of stable 
equilibrium, could not be altered into aragonite; whereas aragonite, being 
unstable, could easily pass into calcite. Hence calcite shells may be 
preserved in a limestone and even retain their microscopic structure, while 
those made wholly or partly of aragonite may have lost their internal structure 
or may have been entirely effaced. 
His microscopic studies of minerals had usually a chemical side. This 
feature of his work was-especially illustrated by the numerous papers which 
he wrote in the year 1869. He then announced some new applications of the 
microscope to blow-pipe chemistry. He detected and described the minute 
crystals which he had detected in blow-pipe beads. He carried out an elaborate 
investigation into the nature of the liquids observable in various minerals, 
especially in sapphires, rubies, spinels, aguamarines and emeralds, and made 
many measurements of the rate of expansion of these liquids with increase of 
temperature. In the fluid cavities of sapphires he found that the volume of 
the liquid, when heated from 0° to 30° C., expands from 100 to 150, and he, 
consequently, inferred that it must be liquid carbonic acid. In the course of 
these researches, he had occasion to study the zircon, or so-called “jargon,” 
of Ceylon, a mineral in which a remarkable assemblage of distinct elements 
had been shown by spectrum analysis to be present. At first he believed 
that some peculiar and characteristic spectra, which he obtained in the jargons, 
indicated the presence of a new element, to which he gave the name of 
Jargonium. Further examination, however, convinced him that this 
