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March, 1944 THE ANOMALOUS RASE STRENGTH OF THE ,&&THYLAMINES 435 ratus a t the usual pressure. The results are given iii Tables I arid 11, determinations 4 and 5. It is apparent that within the lower precision of these results, there is no significant difference between the constants thus obtained arid those obscrved in runs 1, 2 and 3. I t may be concluded that the ncruracy of the constants is not seriously affectcd by deviations from the perfect gas laws. Although errors due to this factor might be reduced by using an ex1 rapnlaiion procedure, the sensitivity of the dissociation data .obtained in the lowrr pressure range to variations in thc initial pressures' stiggests that very little would be yaiiictl by rc'rniirse to such a method.Suiiiiniiig up, tiLC 11. it appcars that Ihe nicthod descrihrd in this 1)apcr for :iie;wiririg the dissociation of addition coiiipounds yields d )ciat.ion data with the desired accuracy: thc dissoci on coristaiits are estimated to be reliable to 2% and the heat of dissociation to 0.1%. The optimum pressure range (initial pressure of each component) is 20-30 mm. Operating helow this range (e. g., 10 mm.) does not noticeably affect the experimental values of the constants, hut it greatly increases the probable error. (7) Comparison of the calculated values in runs 5 and 5'illustrates this sensitivity. In the 5 ' series of culculations, 10.07 mm. was used for the initial prcssure instead of the 10.04 (+0.04) actually observed.There is little doubt that the precision of the measurements could be further improved by additional refinements. However, the uncertainty introduced by tieglect of the gas law deviations suggests that higher precision is of uncertain value. Certainly, the field is so new and the questions to be answered are so many that it appears more important now to concentrate on the more urgent probleins and to leave further refinements to such a time as the need for even more accurate data becomes apparent. SummaryAccurate dissociation data of addition compounds in gaseous systems are of considerable interest and value for theoretical organic chemistry. A simple technique for precise measurement of such dissociations has been devcloped and tested by a series of studies oil the dissociation of trimethylamine-triinethylboron. The tests indicate that by this method the dissociation constants can be determined to 2% and the heat of dissociation DETROIT, MICHIGAN RECEIVED AUGUST 7, 1943 to 0.1%.

The vapor phase dissociation of formic and acetic acids has been studied in the pressure range below one-tenth atmosphere and the temperature range of 50-150°. The data are summarized by the equations logic K --3083¡T + 10.743 (formic acid); logw K = -3316/T + 10.834 (propionic acid). The data for formic acid agree with the results obtained by Coolidge.The data for propionic acid yield a heat of dissociation much lower than that reported by MacDougall. These data combined with those previously published for acetic acid suggest that the hydrogen bond strength in the acids considered increases in the order HCOOH < < CH3COOH < C2H5COOH. It is suggested that the strength levels off and remains essentially constant beyond propionic acid. Other data are summarized which support this order.