Dr. Andrews o« Heat produced in Metallic Substitutions. 93 



the universities than they are at present. I have laboured to 

 show the manner by which mathematicians are there made. 

 No scheme can be devised to put the non-academic student on 

 a level with the more fortunate academic one, but it has been 

 my desire to contend, and my wish to prove, that all has not 

 been done for the self-taught student that might be, and, as I 

 think, ought to be done. Books well written on all subjects 

 are within his reach, but the inducements to make him read 

 them are, according to my view, exceedingly circumscribed. 

 It has been attempted to show, that to the non-academic stu- 

 dent, publications, not too costly, containing a number of 

 proper questions, and holding out prizes for stipulated solu- 

 tions, supply, to a certain extent, the place of college exami- 

 nations, prizes, &c. ; each excites a spirit to excel and becomes 

 an incentive to mental exertion. At present the Lady's 

 Diary is the only work of the kind published in Great Bri- 

 tain ; consequently, as I think, non-academic and self-taught 

 students are not properly encouraged ; the public does little 

 or nothing for them ; the societies so often referred to might, 

 it is thought, very easily supply this national defect, if they 

 could be induced to do so. I fear my immethodical remarks 

 will not effect much, but I will indulge the hope that they may 

 call the attention of some one to the subject who has the power 

 as well as the wish to render some service to the self-taught 

 and non-academic student. 



XIII. Note on the Heat produced during Metallic Substitutions. 

 By Thomas Andrews, M.D., M.R.I.A. 



THE following general principle, which is a probable con- 

 sequence of my former investigations*, I have succeeded 

 in establishing by numerous experiments. It is a very simple 

 law, and refers to chemical reactions, the interpretation of 

 which is equally simple. The principle may be thus stated : — 



" When one and the same metal displaces another from 

 any of its neutral combinations, the heat developed is always 

 the same ; but a change in either of the metals produces a 

 different development of heat." 



The most important source of error to which the experi- 

 ments in proof of this principle are liable, arises from the 

 formation of voltaic circles by the precipitated metal with the 

 excess of the other metal. The slight voltaic action thus in- 

 duced produces a sensible amount of heat; but by conducting 

 the experiments under suitable conditions, the error from this 

 cause may be almost entirely avoided. 



Belfast, June 29, 1844. 



[* See Phil. Mag. S. 3. vol. xix. p. 183.— Edit.] 



