iv PREFACE. 



so essentially slow, and so full of pitfalls, that the serious attempt to draw 

 conclusions from the data in hand must be deferred. It appears, however, 

 that in all cases the physical pores of a solvent like water are effectively 

 closed by a solute, but that the amount of closure is dependent on the char- 

 acter of the salt and the density of the solution in a way not to be easily 

 surveyed. Thus a dilute solution may show greater cloture than a concen- 

 trated solution of the same salt, due no doubt to the formation of hydrates 

 effective in this respect. It appears also that the diffusion coefficients 

 obtained from direct manometer experiments in the lapse of years are not 

 at once comparable with the results for the divers in the lapse of months, 

 all of which disparities will need long-continued observation. 



My thanks are as usual due to Miss Ada I. Burton for most efficient 

 assistance through the whole of this work, both in its experimental and 

 editorial parts. The data of Chapter IV, requiring a high order of patience 

 and accuracy, both as to observations and computation, have been largely 

 contributed by her. 



Carl Barus. 



Brown University, 



Providence, Rhode Island. 



