3()7 



In our experiments the speed of distillation often did not exceed 

 about six drops every minute. In some cases, e.g. with toluene, it 

 was impossible to distil from the product of commerce a fraction, 

 fulfilling all conditions; in such cases the substance was prepared 

 in some other way, e.g. the mentioned toluene by dry distillation 

 of purified calciumphenylacetate ; etc. In the series of compounds 

 described, several were taken from the collection of scientific prepa- 

 rations of this laboratory ; from these also only the small, constantly 

 boiling fraction was used for our purpose. 



§ 2. Notwithstanding the by no means negligible differences of 

 the boilingpoints observed, the specific gravities of the liquids in 

 most cases differed only slightly or not at all from the data, given 

 in the literature. If this was the case, — and we always controlled 

 this by some pycnometrical determinations at 25° C, — the specific 

 gravities at other temperatures were calculated from the expansion- 

 formulae eventually already determined. If the direct determination 

 of cP^'' did not agree with the number, given in literature, or if the 

 expansion-formula was not known accurately enough, three specific 

 gravities, e.g. at 25°, 50°, and 75° C. or at a higher temperature, 

 were determined pycnometrically, and from these determinations an 

 empirical equation of the second degree with respect to t, was calcu- 

 lated. This is completely sufficient here, because the specific gravities 

 were all abbreviated with three decimals: an account of the densities 

 in more than three decimals, must be esteemed valueless here, with 

 respect to the obtained accuracy of the measurements. With most 

 liquids, the mean decrease of the specific weight for 1° C. does not 

 differ largely from 0,001. For temperatures of — 70' and above 

 100° C. it was often necessary to extrapolate by the aid of the 

 established empirical formulae ; although conscious of the uncertainties, 

 which are always connected with such extrapolations, we are of 

 opinion that we have not introduced here in this way errors of appre- 

 ciable amount, because for these values such an error could manifest 

 itself only in the third decimal place, and dilatation of the liquids 

 occurs ordinarily in so regular a way, that the probability of heavy 

 errors is thus highly diminished by this circumstance. 



Moreover another way was not available at this moment, if not 

 with large sacrifice of time and labour. 



§ 3. In the following the obtained results are collected in tables. 

 For the value of 1 mm. mercury at 0° C, 1333,2 Dynes (45°), was 

 calculated, and this value was used in all further calculations ; in the 

 tables all numbers for / and [i are adjusted by the necessary corrections. 



