24 REPORT~18G9. 



least acid salt be formed by the combination of m atoms of acid with n atoms of 

 base, the quantity of base which is so converted will be 



»/3,r 



mci' 

 and the quantity of base remaining in its natural state will be 



oifix 



where b^ denotes the original quantity of the base present in the given bulk of 

 solution. 



Now let r„ be the rotator]/ j^otver of the base, or, in other words, the actual 

 rotation produced by a imit of length of solution containing in a vmit of bidk a 

 imit of base, and let rj be the rotatory power of the salt, the unit of salt being the 

 amount of salt produced from the imit of base. Then if the length of the colvmin 

 of solution through which the light is transmitted be still unity, the rotation which 

 would be produced by tliat part of the base which is converted into salt, if it 

 existed alone in the solution, would be 



nfi.v 



■ — "'"d 

 mcc. '' 



and the rotation which would bo similarly produced by the unconverted base 

 would be 





Hence, assuming that these effects are produced independently of each other, we 

 have as the value of the total rotation produced by the acidulated solution, 



nBx I , nBx\ 



-^r,+ f fto--^)'■o• 

 «^« 11^0 met, I 



Now, since &„ ?•„ is evidently the rotation produced by the unacidulated liquid, 

 the change in rotation caused by acidulation is 



Hence, if we measure along the axis of abscissae distances representing the 

 values of x in a series of experiments, and raise ordinates proportional to the 

 change in rotation caused by the addition of the acid, the locus of the extremities 

 of these ordinates will be a right line, provided that the quantity of acid be not 

 greater than that required to convert the whole of the base into the lowest or 

 least acid salt. 



Suppose, now, tliat this limit has been attained, and that we continue the addi- 

 tion of the acid. By tliis continued addition we shall commence the formation of 

 a new salt from the first salt, ju.st as before we formed the first salt from the base. 

 And if we continue the foimer construction, we shall still have as the locus of the 

 extremities of the ordinates a right line, but not in general the same right line. 

 The completion of the first salt is indicated by the transition from the one line to 

 the other. The same reasoning applies to every subsequent salt, the completion of 

 each definite compound being in general indicated by a break, in the locus. 



The author illustrated this reasoning by a diagram, exhibiting the action of 

 arsenic acid upon brucia. 



On the Chemical Action of Light discovered hy Professor Tyndall. 



Btj Professor Aug. Moreex. 



[Printed in extenso among the Reports, see p. 66.] 



On the JSfumer iced Relations hetiveen tlie Weive-Lengths of the Hydrogen Says. 

 By G. Johnstone Stonet, M.A., F.E.S. 



