2 INTRODUCTION. 



of compounds built up of dissimilar elements; this, however, was 

 not the writer's purj)Ose. And a glance at the tables will show that 

 the arrangement is essentially dilTerent. All the hydro-carbons are 

 placed together, arranged, as fiir as possible, in regular series, with 

 reference to their chemical relations. So also all compounds con- 

 taining carbon, hydrogen, and oxygen, united together without the 

 presence of other elements, and so on. The Table of Contents will 

 doubtless prove a sufficient key to the arrangement. 



That the tables are absolutely complete, is not claimed for them, 

 especially as their scope is limited. They contain no determinations 

 of specific gravity for solutions, and all such must be sought for in 

 Storer's " Dictionar}' of Solubilities." And they contain but few deter- 

 minations of natural minerals, most of the silicates, especially, being 

 omitted. Again, numerous old determinations of specific gravity are 

 left out, as having been rendered utterly valueless and supplanted 

 by more recent and more accurate observations. In short, all that is 

 claimed for the work is, that it forms a practically complete table of 

 the specific gravities of artificial compounds of definite constitution : all 

 else in the table is gratuitous. There are some determinations of 

 specific gravities of natural minerals, chiefly those of comparatively 

 simple composition quite full sets of observations for most of the 

 chemical elements, and a good number of determinations for the lead- 

 ing alloys. So with the boiling points and melting points; they have 

 been added merely to supplement the specific gravities : but as far as 

 the table claims thoroughness, it will be found complete. Up to June 

 1, 1871, little has been omitted, except in the cases mentioned above. 



There is one obvious objection to the method of arranging deter- 

 minations of physical constants in tables. Details cannot be given. 

 In many cases there are important questions of detail to be considered. 

 How was a determination made? How was the material obtained? 

 And if several isomers are grouped under one name — as for instance 

 the several butyl alcohols, or the isomeric bodies known as cumol — 

 which one is meant when a specific gravity is given ? All these ques- 



