40 REPORT — 1877. 



and less violent than in the Midlands. No doubt a large portion of the atmospheric 

 electricity which is generated by the evaporation and friction of the waters of the 

 sea is silently discharged through our damp atmosphere, and thus eludes obser- 

 vation. 



Miscellaneous. 

 Experiments illustrative of the Flight of Projectiles. By P. Braham. 



Suggestion for a new Polar Expedition, with a proposed Boute. 

 By Commander Cheyne. 



On the Tides of Port Louis, Mauritius, and Fremantle, Australia. 

 By Captain Evans, F.B.S., and Sir W. Thomson, F.B.S. 



Note on the Volumes of Solutions. By J. A. Ewing and J. Gordon 

 MacGregor, M.A., D.Sc. 



In a paper by the authors, published in vol. xxvii. of the 'Transactions of the 

 Royal Society of Edinburgh,' containing an account of experiments on the density 

 and electrical conductivity of certain saline solutions, notice is directed to the fact 

 that the density of very weak solutions of sulphate of copper and sulphate of 

 zinc is greater than it would be on the hypothesis that the anhydrous part of the 

 salt dissolves without increase of volume in the whole of the water present, inclu- 

 ding the water of crystallization. On the other hand, the density of comparatively 

 strong solutions is less than this hypothesis would make it. From this it follows 

 that if a small quantity of one of these salts in the anhydrous state were added 

 to water it would cause contraction, while a large quantity of the salt would 

 produce expansion. The amount of such contraction, however, as indicated by 

 observations of density, was so small that the authors were unwilling to speak 

 positively as to its existence until they had applied a direct volumetric test. 

 They have now done so, with the result of confirming the deduction drawn from 

 their earlier experiments. 



The apparatus consisted of a large bottle 2744 c.cm. in capacity, through the cork 

 of which projected a vertical tube of OGG cm. bore. The bottle, as well as part of the 

 tube, was filled with distilled water, and the salt was introduced through the tube 

 in quantities of 10 grammes at a time. The resulting change of volume was shown 

 by the rise or fall of the liquid in the tube. In order to eliminate the effect of 

 variations of temperature, a second precisely similar bottle and tube were prepared 

 and filled with water, and the two were placed together in a large tub full of 

 water. The second bottle acted as a thermometer, and the expansion or con- 

 traction due to the introduction of the salts into the first bottle was indicated by 

 the difference between the changes of level in the two tubes. After the introduc- 

 tion of each dose of salt the bottle was rolled about for a time so as to secure 

 thorough diffusion and solution, and then an interval of at least six hours elapsed 

 before readings were taken, in order that the heat given out by the hydration of the 

 salt might be dissipated. 



The following results have been obtained in the case of anhydrous sulphate of 

 copper. The maximum contraction occurs when the proportion of anhydrous salt to 

 water is about 1 to 50, and the amount of contraction is then 0-00043 of the original 

 volume of water. As more salt is added, the solution begins to expand, and 

 with 1 part of salt to 18 of water the volume is equal to that of the water originally 

 present. After this, any further addition of salt produces expansion beyond the 



