THE APPLICATIONS OF CRYSTALLOGRAPHY 

 TO PHYSICAL CHEMISTRY. 



THE chemistry and physics of gaseous substances have 

 been for so many years the subject of such careful 

 study that we are now in possession of complete and highly 

 organised working hypotheses respecting most of the pro- 

 perties of gases. And although it can hardly be said that 

 the facts up to the present elicited from the study of liquid 

 substances have led to the establishment of satisfactory 

 theories concerning the molecular physics of liquids, yet 

 the pioneer work has been so well done that we are within 

 measurable distance from the acquirement of very complete 

 knowledo-e of the molecular constitutions and molecular 

 tactics of liquids ; the methods of attacking the problems 

 involved, which have been based on such properties as the 

 molecular volume, refractive power, capillarity, viscosity, 

 thermal properties, etc., are of so powerful a nature that the 

 situation will probably be to all intents and purposes cap- 

 tured within a very few decades. 



Whilst, however, the great measure of success which 

 has attended scientific inquiries into the molecular properties 

 of liquids and gases must stand as an abiding monument to 

 the industry ot the nineteenth century, our comparative 

 ignorance of the chemistry of the solid state will, in years 

 to come, testify to that high order of unassailability peculiar 

 to the questions at issue which seems to have almost nullified 

 all attempts to learn something of this department of chem- 

 istry. That we know multitudes of facts respecting solids 

 cannot be denied, but it is scarcely an exaggeration to say 

 that the framework of chemical theory surrounding those 

 facts is of too flimsy a nature to hold them together, and 

 the absolute value of the theories as affording indications 

 of the lines upon which future work should be conducted is 

 extremely small. We learn little of scientific importance 

 from most of the physical or chemical facts at present 

 known about solids ; such a fact as that the great tough- 



