470 Messrs. V. Harcourt and Esson on the [Nov. 1C, 



mula is most likely C Z6 H 32 ; and if bromine forms the bibromide, C 16 H 32 Br 2 , 

 from wbich by the action of caustic soda H Br is abstracted, the com- 

 pound analyzed would be C 16 H 31 Br, which formula requires 26'4 per 

 cent, of bromine, whilst the analysis gave 25*8 per cent. ; the hydrocarbon 

 would then be an isomer of cetene. 



III. " On the Laws of Connexion between the conditions of a chemical 

 Change and its Amount/' By A. VERNON HARCOURT and W. 

 ESSON. Communicated by Sir B. C. BRODIE, Bart., F.R.S. 

 Received September 5, 1865. 



(Abstract.) 



The amount of a chemical change under any conditions which allow of 

 its completion, depends ultimately upon the amount of that one of the 

 substances partaking in it which is present in the smallest proportional 

 quantity. But if the change be arrested before any one of the reagents is 

 exhausted, its amount depends upon the conditions under which it has oc- 

 curred. These conditions, in the simplest cases, are the quantity of the 

 several reagents, their temperature, and the time during which they have 

 been in contact. The laws of connexion between these conditions of a che- 

 mical change and its amount are the subject of an investigation upon which 

 the authors have entered. An account of the first stage of this investiga- 

 tion is contained in the present paper. 



Although every chemical change is undoubtedly governed by certain 

 general laws relating to the conditions under which it occurs, the number 

 of cases in which the investigation of these laws is possible is extremely 

 limited. For it is requisite both that the amount of change should be 

 readily estimated, and also that all the conditions affecting it should be sus- 

 ceptible of measurement and of such independent variations as must be 

 made in order to determine the separate influence of each. 



The first reaction chosen for investigation was that of permanganic acid 

 upon oxalic acid. It is well known that when a solution of potassic per- 

 manganate is added to a solution containing an excess of oxalic acid and 

 sulphuric acid, a change takes place which in its final result is represented 

 by the following equation : 



K 2 Mn 2 O 8 +3H 2 SO 4 +5H 2 C 2 4 =K 2 SO 4 + 2MnS0 4 +10C0 2 +8H 2 0. 

 This reaction occurs at the ordinary temperature ; it is thus comparatively 

 easy to keep the temperature of the solution absolutely constant during its 

 progress. It occupies, under a due arrangement of other conditions, a con- 

 venient interval of time, and can be started and terminated at a given 

 moment. The reagents are readily obtained in a state of purity, and can 

 be accurately divided and measured as liquids. Lastly, no other condition 

 besides those named affects the result : when each of these is fixed, the 

 amount of change observed in successive experiments is always the same. 

 Nevertheless this reaction, as appeared in the course of its investigation, is 



