7 hu fe 99 MA, 
Lie ; 
Sa The true Matt pressure is always higher; it increases 
saeh with the narrowing of connecting tube from boiling tube to | condenser, 
(2) with decrease of the working pressure, vi 
ae (3) with the increase of the distillation strength, 
R or in going back to the common cause of these three factors: — with the valctuat of 
a “the vapour current in the connecting tube. How astonishingly high the velocity of 
z KS ‘the vapour can become, is shown by the following table. The figures denote metres 
ie per second! The amount of distillate in each case was ace per second. Tee 
pS Pee widths of connecting tube were inserted. 
ee Distillation at: 760. Pesan Ge 2 0.1 mm. Hg. 
& A RG RN dace eer Condenser tube 20 mm. wide: ne ) 
SOs Cy eat ole Reece NOT uh Pau Lo 78 nT 76 136 
ee eee wee le OAR aoe N78 BOB. h cine 
Pin bY aS | iS e a _ Cooling tube 7 mm. wide: Ne ae 
Se Dibenzylketone . 0.21. 6.36 19.97 56.6 1002 
Wee or Posairole 2 UPA 709-5 22.20 A684) ATI 
Ree ee i GAA AOA TAD ATS Se 
<9 2° Pate Se a Tae Cooling tube 5.5mm. wide: 
meee mceayiketone 5.) Ooo.” 10.3127) 32.36. 91.75 1620. 
fee Anpsairole 2.) 0.39 LEAD? ego TORE 1801 
ee Sg RS RINS Bs oes 15.2 235.3 669 ny aes 
ay ane 
“All vabote peietics over about 10 aisee must lead to noticeable | ‘choking back”, 
> ie. .. the raising of the pressure in the boiling tube; in such cases also, reading off 
the pressure behind the receiver is decidedly faulty. That the mistakes occaSionally - 
can be greater than even the pressure read off, is not astonishing after this. 
Inthe boiling tube, temperature differences indeed were observed, but no. differences 
ae in ‘pressure were present, not because no ‘pressure differences were there, but because 
no sufficiently sensitive ‘measuring method could be applied. For below 20 mm. working 
_ pressure, a difference. art? in femperature corresponds only to 0.3 mm. and less, 
4 "difference in ‘pressure. , ' 
‘The final results of the investigation, — and its discussion in connection with the 
_ investigations of Hansen’) is expressed as follows: Ae 
“It has _again ‘become clear, that in the dynamical process of boiling point deter- — 
ce mination, not only the first source of error coming into one’s mind is to be attended — 
-- to—which has finally led to the demand, to measure the boiling pressure at the point 
: where the boiling | temperature is read off. Rather it is seen that in observing this 
condition in boiling point investigations, under certain conditions (very low pressure, 
_ high ‘vapour velocity) it is not further possible to effectively determine the equilibrium 
_ of liquid and vapour thermally and volume- -energetically. In other words there is no 
_ infallible determination of the boiling point according to the dynamic process, but it 
can ‘still only be a matter of knowing the limits of accuracy of the method used, and 
to yee them below a certain order of magnitude.” 
_ The following rules are recommended Ap the pierica! carrying out of the dynamical 
- boiling point estimation: — | 
1) Zeitschr. f piigeile Chem. 74 (1910), 65. 
