316 Royal Society :— 
the quantity or 480 grains of salt were dissolved, the pure water, 
as compared with the solution, lost in the proportion of 5 to 3. 
The third proposition is proved by the fact that a solution of 480 
grains of nitrate of potassa in 4 ounces or 1920 grains of water lost 
in twelve hours 95 grains; while a solution of the same strength of 
hydrochlorate of soda lost only 70 grains ; and again, a solution of 
loaf-sugar, in which 480 grains were dissolved in 1920 grains of water, 
lost in 20 hours 175 grains, while a like solution of hydrochlorate of 
soda lost only 117 grains. 
The fourth proposition is proved by the fact that 480 grains of 
gum-arabic dissolved in 1920 of water had a specific gravity of 1-072, 
while a solution of hydrochlorate of soda of like strength had a spe- 
cific gravity of 1-149; after 11} hours, the former had lost by eva- 
poration 71 grains, while the latter had lost only 50 grains. Here, 
therefore, the solution of the lighter specific gravity was less retarded 
in its evaporation than the heavier solution. In contrast with this 
fact, a solution of hydrochlorate of ammonia of 480 grains to 1920 
grains of water, having a specific gravity of only 1-060, lost by evapo- 
ration, in 8 hours and 44 minutes, 17 grains, while a like solution of 
hydrochlorate of soda lost 24 grains. Here, then, the solution of 
lighter specific gravity was more retarded in its evaporation than the 
heavier solution. The conclusion is decisive that specific gravity has 
no necessary connexion with the phenomena. 
The fifth proposition is proved by the fact that in the following 
solutions of salts of potassa, all of the same strength (namely 1 salt 
to 10 water), a difference in the amount of evaporation in each will 
be observed to have taken place; and it must be borne in mind that 
in solutions so weak we cannot expect that difference to be very great. 
The reason for employing weak solutions was the necessity for 
having all of the same strength, one in ten being the extent to which 
the least soluble salt submitted to examination, namely, the sulphate 
of potassa, will, at a low temperature, dissolve. grains. 
Acetate of potassa lost in 35 hours . . . « 145 
Bicarbonate of potassa lost in 35 hours . . . 131 
Carbonate of potassa lost in 35 hours . . . 115 
Ferro-cyanate of potassa lost in 35 hours . . 110 
Hydrochlorate of potassa lost in 35 hours . . 98 
Nitrate of potassa lost in 35 hours . . . . 117 
Sulphate of potassa lost in 35 hours. . . . 1382 
Tartrate of potassa lost in 35 hours . . . . I51 
The above solutions were next made all of one specific gravity, 
namely 1:060, temp. 62° Fahr., instead of being all of one strength, 
and the following is the result :— grains. 
Acetate of potassa jostin 163 hours . . . . 40 
Bicarbonate of potassa lost in 163 hours. . . 45 
Carbonate of potassa lost in 163 hours . . . 39 
Ferro-cyanate of potassa lost in 163 hours . . 41 
Hydrochlorate of potassa lost in 163 hours . . 32 
Nitrate of potassa lost in 163 hours . . . . 39 
Sulphate of potassa lost in 163 hours. . . . 42 
Tartrate of potassa lost in 163 hours . . . . 43 
