A SIMPLIFIED MIXTURE CALORIMETER H. S.
VAN
KLOOSTER
Rensselaer Polytechnic Institute, Tmy, New York
T
HE CUSTOMARY outfit for determining heats of neutralization consists of a highly polished cylindrical vessel of silver of 600 cc. capacity surrounded by co-centric metal or glass cylinders placed in a larger water-6lled jacket. In this calorimetric vessel one places 250 cc. of fourth-normal acid while the same amount of base is introduced into a second container. At the proper time the base is allowed to flow into the calorimeter. This arrangement necessitates the use of two thermometers, one for the upper and one for the lower vessel, and the evaluation of the readings of one thermometer in terms of the other. It occnrred r to the writer that the use of a second thermometer could be eliminated and a t the same time a saving in materials effected by bringing both liquids in close contact with each other prior to the mixing. 4 i The apparatus sketched in Figure 1 has been in use for a considerable time and with satisfactory results both for private and for student work. It consisti of an 8" wide-mouth vacuum flask of 400-cc. capacity fitted with a protecting jacket of corrugated cardboard in which is placed the mixing chamber. The latter is formed from a glass cylinder about 7" long and 1.5" wide, tapered down and rounded a t the base to about 1" diameter so that it will slip tightly over a cork (or rubber) stopper. A similar, thin-walled glass tube of 1" diameter, likewise tapered and rounded a t the base so as to insure an easy and tight fit, serves as the inner calorimetric vessel. The outer tube is held in position by cork collars sealed to the Dewar vessel, and heat Iosses are minimized by cardboard cover@ with tin foil, as indicated in the figure. From a 25-cc. pipet, 25 cc. of acid is introduced into the annular space between the tubes while the inner tube contains the same volume of base. After inserting the Beckrnann thermometer in the center of the inner compartment, the system is allowed to come to equilibrium and readings are taken a t regular intervals of time. At the proper moment the inner tube is released by a slight turning movement and raised up and down a few times to insure a thorough mixing. The readings are continued in the usual way for some time and the data plotted on graph paper. In Figure 2 are recorded the readings from student observations both for the usual procedure (250 cc. of base and of acid) and for the simplified method in which only 25 cc. of each reagent is empioyed. As is seen from I the curve on the right, the temperature rise is practiFrcrme 1 cally instantaneous and can be readily and accurately evaluated. It can be argued, of course, that since the amounts, any error in the determination of the temquantities used are only one-tenth of the customary perature rise is necessarily multiplied by ten. How285
ever, the advantages inherent in this simplified procedure are such that the results obtained are usually not more than 2 or 3 per cent. diierent from the correct value and the deviations are not greater than those obtained by themethod commonly employed. In case the thin-walled glass cylinder is replaced by a silver cylinder held in a flanged glass tube a better heat exchange is established and more accurate results are obtained. At the suggestion of the writer Mr. A. R. Bayer' has utilized the apparatus described for the determination of the heats of mixing of water and a number of primary alcohols a t room temperature (20') using each time a total volume of 50 cc. of the reacting substances. The results obtained agreed within a few per cent. with those of Bose2who used a different technic and amounts of liquid 4 to 6 times as great. Preliminary experiments showed that the new outfit can also be used to great advantage in cases where the usual procedure fails, as for instance in the determination of heats of gelation when rapid or instantaneous formation of gels occurs. A few cases were investigated, e. g., the formation of Baskerville's solid alcohols and the formation of silicic acid gels by the 1
A. R. BAYEn, Thesis, Rensselaer PolytechnicInstitute,June.
1931. 2
Boss, Z.phyrik. Chem., 58, 585 (1907).
addition of acetic acid to dilute solutions of water glass.
