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XLII. Self-recorded Breaks in the Properties of Solutions, 

 By Spencer Umfreville Pickering, F.R.S* 



WHEN investigating the properties of solutions I was 

 desirous of obtaining some method by which the more 

 or less sudden changes of curvature noticed when these pro- 

 perties are plotted against strength might be made to register 

 themselves automatically. Other work has prevented me 

 from following up this subject ; but the method which was 

 obtained seemed to be so satisfactory, that, although it may not 

 be applicable in all cases, a brief note of some preliminary 

 results may be of some interest : moreover it is so simple that 

 anyone possessed of a delicate thermometer and efficient 

 calorimeter can verify the existence of these changes of cur- 

 vature at the expense of a day's work. The method consisted 

 in running a solution into a calorimeter of water with a ther- 

 mometer in it, and photographing the height of the mercury 

 column on a revolving cylinder. The means for this photo- 

 graphing were not at hand at the time, and therefore the 

 thermometer was read through a telescope every half minute 

 instead. The solution was run in from a graduated bottle 

 through a siphon ending in a very fine point and dipping 

 under the surface of the water in the calorimeter. The 

 amount of solution which had been run in was read off at 

 intervals, and thus the composition of the liquid in the calori- 

 meter at any moment could be deduced. The calorimetric 

 liquid was stirred continuously by a stirrer worked by a 

 water motor. The substance investigated was sulphuric acid. 



If the heat of dissolution of different strengths of acid shows 

 changes of curvature at certain points, as it does according to 

 my previous work (Chem. Soc. Trans. 1890, p. 101), then 

 the rate at which heat is evolved when the acid is run con- 

 tinuously into water must show changes of curvature also. 

 Whether the latter will be recognizable or not will depend on 

 the magnitude of the former changes, and also on their mag- 

 nitude as compared with the total heat evolved. 



As instances favourable for recognition, the well-marked 

 breaks with very weak solutions of the acid were taken; a 5 or 

 10 per cent, solution being run into 550 cubic centim. of water. 



I need only give two experiments as examples illustrating 

 the existence of the two extreme breaks indicated by my 

 former work. 



Fig. 1 shows the results of one series. In the upper 

 drawing the thermometer-readings are plotted against time, 

 and in the lower the strength of the calorimetric liquid is 

 * Communicated by the Author. 



