Section III., 1885. [ 15 J Trans. Roy. Soc. Canada. 



lY.— On the Density of Weak Aqueous Solutions of Certain Salts. 



By J. Gr. MacGtRegor, D.Sc. 



(Presented May 28, 188.3.) 



The following experiments were made with two objects : (1) to determine whether or 

 not there are solutions of the salts used, given A'olvimes of which are less than the volumes 

 at the same temperature of the water which they contain ; and (2) to find how the den- 

 sity of very weak solutions varies with their strength. 



Professor Ewing ' and I had found, by two experimental methods, that sufficiently weak 

 solutions of siilphate of copper contain amounts of water whose volumes if free would be 

 greater than those of the solutions themselves ; and that anhydrous copper sulphate, added 

 in small quantities to water, produces solutions of smaller bulk than the original water. 

 We had also " found that certain somewhat rough density-measurements had indicated the 

 same peculiarity in the case of zinc sulphate. It seemed desirable therefore to subject this 

 salt to careful experiments and to extend the investigation to other hydrated salts. 



The data which we possess as to the variation of the density of solutions with their 

 strength, do not generally extend to weaker solutions than those which contain 2 or -3 per 

 cent, of salt, and are insufhcient to settle the question. I have, therefore, made observa- 

 tions in the case of zinc sulphate and other salts, which both determine the question of the 

 possession of the peculiarity referred to above, and supply a portion of what has hitherto 

 been lacking in our knowledge of the phenomena of their solution. 



My apparatus consisted of four dilatometers, Avhich were large glass bottles (com- 

 monly called Winchester quarts), with glass tubes fitted in their necks. The bottles had 

 capacities of about 2,600 c.c. The glass tubes were about 2.5 cm. in length and 04 sq. cm. 

 in section, and were chosen so as to be as uniform in bore as possible. They were fitted to 

 the bottles by means of India-rubber stoppers, and fitted so tightly that there could be no 

 danger of any relative displacement of tube and bottle. The rubber stoppers were held 

 fast to the bottle by wires. Their inner ends were hollowed conically, and the glass tubes 

 started from the summits of the conical hollows, so that air bubbles could easily be made 

 to pass up the tubes. At their upper ends the tubes widened into funnels. Fine scratches 

 on the tubes served as zero marks. The bottles stood in a large zinc bath up to their 

 necks in water. The dilatometers were calibrated by being filled with distilled water of 

 known temperature, from measuring vessels whose volumes were known. The one used 

 in calibrating the tu.bes was so divided that changes in the volume of the water it con- 



' Tran.s. Roy. Soc. Edin., vol. xxvii. (lS7r.) p. .")1 ; Reports Brit. Asso. (1877) ; Trans. Roy. .Soc. Canada, vol. ii. 

 (1884)sec. iii. p 09. 



- Trans. Roy. Soc. Edin., vol. xxvii. (1873) p. 51. 



