Rotatory Polarization of Liquids. 403 



Lastly, I was indebted to the kindness of Professor Marignac 

 for a certain quantity of monohydrated sulphuric acid (HO SO 3 ) 

 prepared by himself, upon the purity of which I could therefore 

 reckon. This acid gave, in two series of experiments, the fol- 



lowing results : — 



HO SO 3 . Water. Ratio. 



7 9 20 0-750 



7 15 9 40 0-750 



The following are the observations of the first series; those of 

 the second present no difference one from another. 



Acid (HO SO 3 ). Water. 



16 15 9° 25 6 50 17° 40 8 20 9° 20 



. 16 20 9 20 7 17 40 8 20 9 20 



16 25 9 30 6 55 17 30 8 20 9 20 



16 30 9 20 7 10 Mean rota tion . 9 20 

 16 25 9 20 7 5 

 16 20 9 20 7 





Mean rotation . 7 



The ratio of 7° to 9° 20' is 0*750. 



Later, having wished to reserve some of the same acid for new 

 experiments, I found a sensible increase in its magneto-rotatory 

 power, which had become 0*761 ; a third experiment gave 0*768, 

 and a fourth 0'774. Suspecting that these changes proceeded 

 from alteration produced in the acid by hygrometric water ab- 

 sorbed every time the acid was transferred from the experimental 

 tube to the bottle in which it was kept, and vice versa, I took a 

 portion of the same acid which had not been used. I took care 

 to introduce it into a tube the two disks of which were carefully 

 sealed so as to cut off all communication with the external air. 

 I submitted it at several different times to the action of the mag- 

 net; and I always found the coefficient 0-750, or at least one 

 very near this, such as 0*749 and 0*751. 



The very remarkable difference between the coefficient of mag- 

 neto-rotatory polarization of the Paris sulphuric acid (0*800) 

 and that of Prof. Marignac' s monohydrated sulphuric acid (0*750) 

 appears to me the more astonishing from the density of the two 

 acids being almost the same, — that of the Paris acid being 1-812 

 at 13° C, and that of Professor Marignac' s acid being 1-832 at 

 20°. However, the Paris acid presents a slight brownish tint, 

 and has a certain empyreumatic odour, which seems to indicate 

 the presence of some foreign substance ; while the other acid is 

 perfectly colourless and transparent, and has not the slightest 

 odour. 



