129 



3. Specific gravity bottles and counterpoises. 



4. Thermometers of various degrees of delicacy and range, for 

 ascertaining freezing, temperate, and boiling points. 



5. Test tubes for use, in connexion with these thermometers, as 

 well in freezing mixtures as over the spirit lamp. 



6. A barometer. 



7. Various salts and other soluble substances, furnishing, when in 

 solution, the materials for examination. 



The mode of procedure which I have adopted has been, to state 

 my facts in the form of propositions, and to prove each of these 

 propositions by experiments. 



The propositions are as follows : 



1st proposition. That in many aqueous solutions of salts and 

 other soluble substances evaporation is retarded, as compared with 

 the evaporation of water. 



2nd proposition. That in solutions of salts which retard evapora- 

 tion, that retardation is in proportion to the quantity of the salt 

 held in solution. 



3rd proposition. That different salts and other substances soluble 

 in water have different degrees of power in retarding its evaporation. 

 4th proposition. That the power of retarding evaporation does 

 not depend on the specific gravity of a solution. 



5th proposition. That in aqueous solutions of salts, the power of 

 retardation does not depend on the base, whether we compare solu- 

 tions containing like weights of the salt, or solutions of like specific 

 gravities. 



6th proposition. That in aqueous solutions of salts, the power of 

 retarding evaporation does appear to depend upon the salt radical or 

 acid, although the retardation is not altogether independent of the 

 influence of the base. 



7th proposition. That salts with two equivalents of an acid have a 

 greater power of retarding evaporation than salts with one equivalent. 

 There are, however, exceptions. 



8th proposition. That there are some salts which, being dissolved 

 in water, do not retard its evaporation, and some salts which, so far 

 from retarding, actually accelerate evaporation. 



The truth or probability of the foregoing propositions is established 

 by numerous experiments, but in this abstract I shall, for the sake 



