785 
Commercial carbon-dioxide was used after purification by distil- 
lation; analysis in an absorptionbulb, filled with iron gauze and 
potassium-hydroxide, showed 96°/, CO, 
The results of the experiments are here given: 
EA Bete ve 
ST E See = ä 2 SS 
. | pressure temp. \galv. deflect. 
? in A.U. | in atm. in OG. mm. Ry /Raos 
| | | | 
Sa eeb eten 5301 1.00 
3665 ots 115 271.9 1.225 
SISON a 2e iks 189.9 1.79 
Ue AN Tia TED 149.8 | 2.275 
DEB ek Beaune Ges 129.6 | 2.615 
| 
2535 | 27.3 | 16.2 114.6 2.95 
Exposures ranged from 1,5 to 10 mts. An additional series of photo- 
graphs of the green and the blue-violet mercurylines was also made 
upon Agfa-chromatic plates in order to afford a comparison with 
SIERTSEMA’s results. The correspondence was found to be very good: 
Fi Ne Be, Eby Vik 
ORR Rian en 
a in AU. a, !Rs461 (after SIERTSEMA) 
5461 1.00 1.00 
4358 | 1.605 nid 
4047 1.87 1.87 
Determination of the absolute rotatory constants. 
9. It has been mentioned already that the arrangement of the 
apparatus for the half-shadow method does not allow of a direct 
measurement of the angle of rotation, so that a calibration with water 
is necessary for an absolute determination of the rotatory constants. 
If the rotatory constant for the wave-length 4 at a definite pressure 
and temperature is Ry for hydrogen and yp for distilled water 
and if the currents used for the two photographs were /77 and /yy 
amp. respectively, then 
a 
134 
