ACCOMPANYING BASIC SUBSTITUTIONS. 
23 
The heat evolved, except in a few instances, did not exceed 3° ; and it was so 
arranged that the final temperature of the liquid was from 0 o, 3 to 1° higher than that 
of the surrounding air, according to the total amount of heat. When a diminution 
of temperature occurred the adjustments were accordingly modified. 
To this method of operating several objections will at once occur, but numerous 
trials have satisfied me that it gives very accurate results when the variations of tem- 
perature are not considerable. The important condition of bringing the two liquids 
precisely to the same temperature in a short space of time is completely attained. 
The principal source of error is the heating or cooling of the alkaline solution during 
the moment of being transferred into the outer vessel, and, if the difference between 
the initial temperature of the fluid and that of the air had been considerable, this 
would have been a serious objection to the process. The difference in question rarely 
exceeded 2°. As a few drops of the alkaline solution remained adhering to the 
interior of the vessel, an excess of 3 grains was taken, which I found to be an exact 
allowance for the loss. A similar portion of the saline solution adhered to the outer 
surface of the brass vessel, but as both liquid and salt were carried off together, the 
error from this cause did not in any instance amount to more than a fraction of a 
hundredth of a degree. The exposure to the air of the caustic solution during the 
few minutes occupied in equalizing the temperatures induced no sensible error. 
The strength of the solution was such, that when a sulphate was employed, the 
entire fluid after mixture contained one per cent, of anhydrous sulphuric acid. 
Hence the required quantity of any salt was obtained by dividing its atomic weight 
by the atomic weight of sulphuric acid. The alkaline liquid contained from y^th to 
2 -^oth of potash more than was sufficient to decompose the salt. 
The thermal value in water of the bulb of the thermometer employed was 6 grains ; 
that of the glass vessel and stirrer (the specific heat of the glass being 0*1 40) 68 grains ; 
making the entire value of the vessels 7 4 grains. The brass vessel being removed 
altogether after the temperatures were adjusted is of course not included. The corre- 
sponding value of the vessels in terms of the liquid obtained is 76 grains. The tempe- 
ratures found are therefore corrected for the vessels by multiplying them by T076. 
Finally, a further correction is required for the specific heats of the solutions and 
precipitates obtained. But as the accurate determination of the specific heat of any 
substance requires great care and much time, I did not attempt to examine sepa- 
rately the specific heat of the product of every operation. I determined, however, 
very carefully the specific heats of the four principal solutions formed, and estimated 
the specific heats of the precipitated oxides (their weights taken in the anhydrous 
state) from the experiments of M. Regnault. The liquids examined were solutions 
(of the normal strength) of the sulphate, nitrate, and acetate of potash, and of the 
chloride of potassium, and their specific heats were found to be respectively 0-973, 
0-975, 0-971 and 0-971*. 
* See Note at the end. 
