Rotatory Polarisation of Liquids. 413 



This Table shows that, in solutions containing only a relatively- 

 small proportion of acid or of water, the magneto-rotatory power 

 increases in the same ratio as the density. Thus the ratio of the 

 actual to the calculated power is 1*032 for the solution which 

 contains, in 10 parts by volume, 1 of sulphuric acid and 9 of 

 water ; for the same solution the ratio of the actual to the calcu- 

 lated density is also 1*032. Similarly the ratio between the 

 actual and the calculated rotatory powers is 1*040 for the solu- 

 tion which contains, in 10 parts by volume, 8 of acid and 2 of 

 Water ; and the ratio of the actual to the calculated density of 

 the same solution is 1*045, or very nearly the same, only a little 

 higher. But if solutions be taken which contain nearly equal 

 quantities of water and acid (such as those comprised between 

 3 tenth parts of water and 7 of acid, on the one hand, and 3 

 tenth parts of acid and 7 of water, on the other), then the ratios 

 between the actual and the calculated rotatory powers become 

 much lower than those between the actual and the calculated 

 densities; and this difference attains its maximum in the solu- 

 tion which contains exactly equal volumes of acid and water. 



As to the rotatory powers themselves, the ratio between the 

 actual and the calculated power does not differ much from one 

 solution to another ; yet it increases slightly, but regularly, with 

 the concentration of the solution. 



It seems to me that we may infer from these observations that 

 the combination of the acid and water diminishes the molecular 

 rotatory power, since the ratio between the actual rotatory power 

 of a certain volume of the mixture and the rotatory power of the 

 same mixture calculated on the supposition of there being no 

 contraction is lower than the ratio between the actual and the 

 calculated density, while the two ratios would have been equal 

 if the combination of the water and the acid had not modified 

 the rotatory power of each. When the proportion of water or 

 of acid is very slight, the ingredients combining in very small 

 quantity and mixing in that one of them which is in excess, the 

 solution behaves like a simple mixture. A very curious fact is 

 the almost complete equality of the ratios between the actual and 

 the calculated magneto-rotatory powers of all the solutions, which 

 would seem to indicate that the chemical action which brings to 

 the magneto-rotatory power of the solution a modification which 

 renders it different from what it would be if the liquid were 

 only a simple mixture, acts sensibly in the same degree upon 

 each ; I say sensibly, because the ratios, though not differing 

 much, show a tendency to increase with the increase of the pro- 

 portion of acid relatively to that of water. 



I submitted to the same experiments two other solutions of 

 sulphuric acid in water, which were kindly supplied to me by 



