24 
DR. ANDREWS ON THE THERMAL CHANGES 
I have collected the experimental results into separate tables. The first column 
of each table contains the name of the salt which was decomposed ; the second, its 
weight; the third, the change of temperature found by experiment; the fourth, the 
same corrected for the vessels or referred to 1000 parts of the resulting mixture ; and 
the fifth, the same referred to 1000 parts of water. 
Salts of Lime. 
Salt. 
Weight. 
Found. 
Ref. to liquid. 
Ref. to water. 
CaO . NO, 
20-6 
-0-34 
-0-37 
-0*36 
CaO. NO, 
20-6 
-0-32 
- 0-35 
-0-34 
CaO . So 0„ . 6HO 
32-7 
-0-35 
-0-38 
-0-37 
CaO . S„ 0 2 . 6HO 
32-7 
-0-31 
-0-34 
— 0-33 
CaCl 
13-9 
— 0-34 
— 0-37 
-0-36 
CaCl 
13-9' 
-0*36 
-0-39 
— 0-38 
CaO . A . Aq 
22-2 
-0-35 
— 0-38 
-0-37 
CaO . A . Aq 
22-2 
-0-35 
-0*38 
-0-37 
The nitrate was cautiously dried on a sand-bath ; in one experiment the solution 
was neutral ; in the other, it had a slight alkaline reaction. The chloride was dried 
at a low red heat, but not fused. Its solution was distinctly alkaline, as this salt un- 
dergoes slight decomposition from the gentlest ignition. Of the acetate, dried in a 
warm atmosphere, 22*64 grains yielded 12*70 grains carbonate of lime, from which 
the required quantity, as given in the table, was calculated. 
The negative sign indicates that when potash displaces the base in these salts, a 
diminution of temperature takes place. The accordance of the results within the 
limits of the errors of experiment is perfect. 
Salts of Magnesia. 
The salts of magnesia are very imperfectly precipitated in the cold by caustic pot- 
ash, and therefore the change of temperature indicated by the thermometer is only 
a part of that produced by the substitution of potash for magnesia. A depression of 
temperature occurred with these salts as with the preceding, amounting to between 
0°*10 and 0°15, in experiments made with the sulphate and chloride and an equiva- 
lent of potash. With a larger proportion of the latter, a greater depression of tem- 
perature occurred, but the substitution appeared to be still incomplete. 
Salts of Barytes and Strontia. 
In numerous experiments with the nitrates of barytes and strontia, and with the 
chlorides of barium and strontium, no change of temperature occurred. The solu- 
tions were taken so dilute that a mere cloud appeared on mixture, consisting chiefly 
of a trace of carbonate. It is true that we have no positive proof that decomposition 
occurs unless stronger solutions are employed and a precipitate formed, but the com- 
parative insolubility of these bases renders it very probable that in all cases substitu- 
tion does take place. 
