Dr. Babington on Spontaneous Evaporation. 315 
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 haye 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 :— 
Ist 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 solutions 
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 of 
brevity, only state the result of one or two experiments in proof of each. 
The first proposition is proved by the fact that a solution of hydro- 
chlorate of soda in the proportion of 480 grains to four measured 
ounces of water, when exposed under the conditions already stated to 
spontaneous evaporation, lost only 33 grains in weight after twelve 
hours’ exposure—while four ounces by measure of water lost 53grains, 
—and after twelve hours’ further exposure lost only 109 grains, while 
the water lost 174 grains; that is, the water, as compared with the 
solution, lost weight in the ratio nearly of 5 to 3. 
The second proposition is proved by the fact that a solution of 
240 grains of hydrochlorate of soda in four ounces by measure of 
water lost in twelve hours 73 grains by evaporation, while four ounces 
by measure of pure water lost 81 grains,—this is in a proportion 
of only about 8 of the latter to 7 of the former ; whereas, when double 
