17 
of Edinburgh, Session 1869 - 70 . 
the possibility of water playing an important part in the con¬ 
stitution of acids and salts. The Professor w r as struck by the 
ideas of his young pupil, and encouraged him to continue his in¬ 
vestigations on the subject. This ultimately led to his splendid 
researches in phosphoric acid, as to which he shows that its three 
varieties—common phosphoric acid, pyrophosphoric acid, and meta- 
phosphoric acid—differed only by containing a different number 
of atoms of water, chemically combined with the an-hydride. He 
followed this inquiry up by researches on water in salts, and 
showed that in a salt the different numbers are held with dif¬ 
ferent degrees of tenacity. His attention was early attracted to 
the diffusion of gases. The manner in which gases mix with each 
other, and the permanence with which the intermixture is main¬ 
tained, are remarkably different from what is experienced in the 
case of liquids; and it is probably to this fact that we owe the 
stability of the proportions in which the ingredients of the atmo¬ 
sphere are maintained, a uniformity which is so essential to organic 
life. The laws also according to which gaseous diffusion takes 
place were found by Graham to be based upon mathematical rela¬ 
tions between their density and their velocity of diffusion, which 
were at once interesting and unexpected. The laws as to the 
effusion of gases into a vacuum, and their transpiration through 
narrow tubes, were also traced by him with indefatigable diligence 
and complete success; and it is a fact of which we may be proud, 
that his first paper on that subject was read before this Society. 
The importance of these investigations, particularly in connec¬ 
tion with the phenomena of osmosis, will probably be seen, in 
its full extent, in the clue which they seem to give to some of 
the most remarkable facts in physiology. The discoveries of 
Dr Graham were due mainly, it may be said, to his close 
adherence to any subject on which he once entered. He never 
quitted it until, by steadfast attention, deliberate consideration, 
and varied experiment, he had extracted out of it every atom 
of scientific truth which it was capable of yielding. The secret of 
his success in this respect was probably not different from what 
may be seen in other eminent discoverers. Newton ascribed his 
achievements not to genius, but to earnest and unremitting atten¬ 
tion; and it must be manifest how much more likely it is that a 
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