150 Mr. W. W. J. Nicol on 



pared with other modes of producing a shower, yields instruc- 

 tive results of this nature. 



Dr. Hammerl has pointed out the great difference in the 

 angular distance of the primary and secondary bows produced 

 by a small change of the index of refraction. The distance 

 between primary and secondary I find to be much greater in a 

 shower of sal-ammoniac solution than in a shower of water. 

 With paraffin the secondary is thrown so far back that some 

 practice is required to bring its circle into view. Extremely 

 beautiful effects are produced by liquids whose globules diminish 

 by evaporation while suspended in the air. The whitening of 

 the primary and the widening of the supernumerary bands 

 are, in these circumstances, highly instructive to observe. 

 Young's conclusion that the white rainbow is due to the small- 

 ness of the falling drops, and not, as Bravais supposed, to the 

 hollowness of the drops, is fully borne out by these expe- 

 riments. 



XX. On Equilibrium in Salt-Solutions. By W. W. J . NlCOL, 

 M.A., B.Se., F.R.S.E., F.C.S., Lecturer on Chemistry, 

 Mason College, Birmingham*. 



THE following paper is a continuation of one I had the 

 honour of communicating to the Chemical Society some 

 time ago, entitled " The Volume Alteration attending the mix- 

 ture of Salt- Solutions "|. In that paper I gave examples of 

 the way in which the volume-change on the mixture of salt- 

 solutions might be applied to the solution of the questions 

 connected with the mode of arrangement of the salts after 

 mixture. I have since been able to investigate more fully 

 Case II. in my previous paper, and I hope to be able to 

 throw some light on the changes in arrangement which take 

 place when solutions, capable of double decomposition, are 

 mixed. Such solutions contain different metals and different 

 *alt radicals : if the two salts be represented by MR and M'B/, 

 then one of the following three states of equilibrium will 

 prevail: — 



(1) No change, 



MR + M'R'. 



(2) Complete double decomposition, 



xMR+yWW 

 become 



^MR' + f/M'R. 



* Communicated by the Author,, 

 t Journ. Ohem. Soc. March 1883. 



