414 Prof. A. De la Rive's Researches on the Magnetic 



Professor Marignac. Both were prepared with monohydrated 

 sulphuric acid (HO SO 3 ) of sp. gr. 1-83211 at 20°, and with the 

 specific magneto-rotatory power (as I have stated above) of 0*750. 

 One of these solutions consisted of HO SO 3 + 5 aq * the other of 

 HO SO 3 + 10 aq. The actual magneto-rotatory power of each of 

 these solutions was compared with its magneto-rotatory power 

 calculated as the mean of the rotatory powers of the water and 

 of the acid (HO SO 3 ) mixed in the same proportion in which 

 they enter into the solution. Similarly the actual densities were 

 compared with the densities calculated on the supposition that 

 no contraction occurred in the mixture. 



HO S0 3 +5 aq. HO S0 3 +K) aq. 



Actual rotation . . 0*943 

 Calculated rotation . 0*906 



Ratio between the two . 

 rotations 



'}. 



Actual density . . 1*413 

 Calculated density . 1*310 

 Ratio between the two"1 -. ,r\yo 

 densities . . J 



Actual rotation . . 0*980 

 Calculated rotation . 0942 



Ratio between the two 1 -. ,q * ~ 



rotations. . . J 



Actual density . . 1*2609 

 Calculated density ;. 1*1903 

 Ratio between the two~l -. ~„~ 

 densities . . J 



We see that, as in the preceding experiments, the ratio be- 

 tween the rotatory powers differs less from the ratio between the 

 densities in just the same degree as the proportions of water and 

 acid in the mixture differ more. What is remarkable is, that, 

 as before, the ratio between the actual and the calculated rota- 

 tory powers is sensibly the same for each solution. 



It must not be lost sight of that the specific rotatory powers 

 are always taken with equal volumes, and that the calculated 

 powers are the means of the respective powers of water and the 

 acid, assuming the mixture to take place without change of vo- 

 lume. If in the calculation account is taken of the contraction, 

 then we find, as might have been expected, that the calculated 

 power is higher (always with an equal volume) than the actual 

 power; in fact it is 0*965 instead of 0*943 for HO SO 3 + 5 aq, 

 and 0*998 instead of 0*980 for HO S0 3 + 10 aq. Thus the mag- 

 neto-rotatory power of the compound is less than the mean of 

 the respective powers of the water and the acid which form the 

 combination. This was already evident from the fact that, with- 

 out taking account of the contraction, the ratio between the 

 actual and the calculated powers is less than the ratio between 

 the actual and the calculated densities. 



