74 TRANSACTIONS OF THE 
Chemistry and Physics also have been profoundly in- 
fluenced by investigations that were initiated at least as 
purely biological. In 1827 the botanist Robert Brown 
noticed that minute particles suspended in a liquid were 
in a continual state of agitation. This observation has 
given meat to the physicists ever since. It was not until 
1889 that the explanation was offered which is accepted 
to-day: that the motion is caused by molecular bombard- 
ment. Again, in 1877 the botanist Pfeffer wished to dis- 
cover some of the facts associated with the rise of sap in 
plants, and began a series of experiments to measure the 
osmotic pressure. He constructed an apparatus to simulate 
as nearly as possible a plant cell. The results of his re- 
searches were published as a monograph. This monograph 
opened a new field to the physiological botanists; and when 
Van’t Hoff at the age of 24 was called to the Chair of 
Chemistry at Amsterdam, his colleague the botanist Hugo 
De Vries called his attention to the work of Pfeffer, and 
requested Van’t Hoff to continue certain parts of Pfeffer’s 
investigations. As a recent writer says, ‘This was the in- 
troduction of Van’t Hoff to the work of Pfeffer, and this 
introduction marks an epoch in the development of Chem- 
istry.”’ Here too the biological influence ends; but the re- 
sult of the influence is so great not only to Chemistry 
and Physics, but to all sciences, that I am tempted to con- 
tinue. Van’t Hoff discovered that a constant relation ex- 
ists between the osmotic pressure and the per cent of con- 
centration of the cane-sugar used in his experiments. In 
this he saw an analogy to the law of Boyle for gases. Then 
“af,” said he, “there is any real relation between solutions 
and gases, the other laws of gas pressure must apply to 
the osmotic pressure of solutions.” Proceeding with this 
theory, he showed that the law of Gay-Lussac, and finally 
the law of Avogadro for gases, applied for most solutions. 
Since the discoveries of Van’t Hoff we really know some- 
thing about matter in solution, but this raises the question, 
“Why is it so important to deal with solutions by the ex- 
act scientific method, or by any method whatsoever? Why 
is a knowledge of solutions so fundamental, not only for 
