''' -2 Dr. L. Bleekrode. On the Determination of the 



were made with the gas, liquefied with the Cailletet pump, and 

 gave similar results. I found D = 15*10 millims., with natrium light 

 </=3*06 millims., n= 1-254 at 10, with daylight n=l*257, also 

 at 10. 



8. Hydrobromic Acid (HBr). 



As mercury is attacked either by the gas or liquid I could not avail 

 myself of the Cailletet apparatus in this case, and on this occasion 

 the faradaic tubes served very well. I obtained great quantities of 

 liquefied gas from a mixture of moist potassium bromide and a small 

 quantity of red phosphorus, separated by a paraflBne stopper from 

 a column of liquid bromine put in subsequently. The gas evolved 

 passed through granulated zinc (to combine with any bromine 

 vapours) and through calcium chloride, and condensed afterwards 

 into the glass cell as a colourless liquid. Tin disks were also here 

 applied for perfect closure, yet were slightly attacked by the liquefied 

 gas. The determinations led to T) = 16*08 millims., with the natrium 

 light (2=3-95 millims., n=l*325 at 10, and with daylight n=l*330, 

 also at 15. 



9. Hydriodic Acid (HI). 



This gas was liquefied in a similar way as above, it being evolved 

 from a moist mixture of red phosphorus iodide and potassium iodide 

 (in a fixed proportion). 



The observations led to D = 15*68 millims., with natrium light 

 d=4*99 millims., = 1*466 at 16 3 *5. 



10. Chlorine (Cl). 



Here also only the bent glass tube could serve, as mercury would 

 not have suffered the contact of the gas without combining with it. 

 I prepared it from a mixture of pyrolusite and hydrochloric acid 

 by gently heating and purifying the evolved gas by a long column 

 of pyrolusite and calcium chloride that would absorb some hydro- 

 chloric acid and moisture escaped at the same time with the gas, thus 

 a perfectly transparent and bright yellow liquid was obtained. 



The observations led to D=15*30 millims., with natrium light 

 <f=4*ll millims., n=l*367 at 14. 



11. Carbonic Acid (C0 2 ). 



I paid peculiar care to obtain as accurate as possible the index of 

 refraction of this liquid substance that has been studied in various 

 ways. I soon became aware in preliminary experiments that the 

 temperature had more influence than in the. other investigations, as 

 might be expected from the circumstance that the critical temperature 

 of liquid carbonic acid is not very far above the surrounding tempera- 

 ture. I preferred therefore the liquefaction in a bent tube by its own 



