— 159 — 



In the case of bodies with high boiling-points (200 and over) an 

 incorrect observation of the steam- pressure may equal a mistake of 

 from 3 to 5 in the determination of the boiling-point; the simplest 

 way of reading accurately, as pointed out by von Rechenberg, is to 

 connect the boiling-flask directly with the manometer. 



The author also explains that in the distillations in an exceptionally 

 high vacuum which have recently been carried out by Fischer and 

 Harries 1 ) and by Krafft 2 ) an incorrect pressure has been assumed as 

 a result of the improper arrangement of the apparatus, as described 

 above. Krafft even went so far as to talk of distillation at o mm., 

 as he calls the vacuum of about 0,001 mm. Apart from the excess 

 of pressure existing in the vessel, a distillation at 0,001 mm. would of 

 itself be an impossibility (as may be shown by a simple calculation) 

 because the steam would be so rarified that no observable distillate 

 would be obtained. For instance, at a pressure of 0,001 mm. the 

 quantity of material which would distil over from a distilling -vessel 

 with an efflux-tube of 8 mm. width, at a distilling- speed of 0,1 m. 

 would be 1 g. in 44,7 hours! Moreover, steam which was rarefied 

 to such a degree would not even- be capable of maintaining the glass 

 and the mercury of the thermometer at steam temperature, and all the 

 steam would be condensed by the thermometer. In any case where boiling 

 points are being taken, or distilling is conducted under reduced pressure, 

 the entire flask should be immersed in the heating-bath, because otherwise 

 too much of the condensate runs down the inner side of the flask. 



The Chemical Action of Light. If menthone in an aqueous- 

 alcoh( >lic solution is exposed for a long time to the action of light, it is 

 hydrolytically split up (as observed by Ciamician and Silber) 3 ) and a decylic 

 acid, together with an aldehyde which is an isomeride of citronellal 

 is formed. At the time the authors regarded this aldehyde as iden- 

 tical w th the mentho-citronellal described by Wallach. Further in- 

 vestigations into the constitution of the aldehyde by the two authors 4 ) 

 were designed to find an answer to the question which of the two 

 following formulae applies to it: 



CH 3 . 

 I. )C:CH.CH 2 CH 2 .CH(CH 3 ).CH 2 .CHO 



CH 3 / 



CH 



II. )CH.CH:CH.CH 2 .CH(CH 3 ).CH 2 .CHO 



CH/ 



*) Berl. Berichte 35 (1902^, 2158. 



2 ) Berl. Berichte 28 (1895), 2 5 8 3; 29 (1896), 1316 and 2240; 33 (1900)* 3217; 

 36(1903), 1690, 4339, 4344; 40(i9O7), 4775* 4779- 



3 ) Berl. Berichte 40 (1907), 2419; Report October 1907, 123. 



4 ) Rend, della R. Accad. dei Lincei 18 (1909), 317. From a copy kindly- 

 sent to us; Berl. Berichte 42 (1909), 15 10. 



