252 Dr, Thomas Thomsons Experiments on the 



Article II. 



Experiments on the Combination of Sulphuric Acid andWater. 

 By Thomas Thomson, M.D., F.R.S., L.&E.,&c., Regius 

 Professor of Chemistry in the University of Glasgow. 



{Read before the Chemical Section of the British Association 

 for the Advancement of Science, Aug. 25th, 1836.) 



It is well knowp, that when sulphuric acid and water are 

 mixed in any proportion whatever, a change takes place iii 

 the temperature, by the evolution of heat, while a chemical 

 combination is formed between the acid and the water. 

 The heat evolved in this case has been universally ascribed 

 to a change in the specific heat of the compound, which, 

 being less than the mean specific heat of the two con- 

 stituents, requires less heat than before to maintain its 

 temperature, and must in consequence appear hot. 



I am not aware of any attempt to investigate this curious 

 subject, except the experiments of M. Gadolin published 

 in the Memoirs of the Stockholm Academy for 1784.^ But 

 as Gadolin no where specifies the specific gravity of the 

 acid which he employed, and as his experiments were made 

 upon diff'erent weights of the acid and water, without any 

 reference to the atomic proportions, it is impossible to 

 deduce any legimate conclusions from these experiments. 

 This is to be regretted, as the experiments of Gadolin 

 appear to have been carefully made, and to have been 

 sufficiently varied. But as the atomic theory was quite 

 unknown in 1784, it was impossible for Gadolin to select 

 such proportions of acid and water as would throw the 

 requisite light upon the combinations. 



To obtain pure sulphuric acid of the requisite strength 

 for my purpose, I distilled a quantity of Nordhausen acid, 

 which had been long in my possession, and which had ab- 

 sorbed so much moisture from the atmosphere that its 

 specific gravity was reduced to l-8375.t Nordhausen acid, 



• Ran och annuirkningar om Kroppars ahsoluta Varme. At' Johan Gadolin. 

 Kong. Vetens. Acad. Handlingar, 1784, p. 218. An abstract of these experiments 

 has been inserted in the Appendix to Crawford's Treatise on Animal Heat, p. 457. 



t The author stated in the Section, in answer to a question from Dr. Dal ton, 

 that English sulphuric acid will not answer for these experiments, in consequence 

 of its containing nitric acid. It contains also arsenious acid, Records, ii. 73 ; and 

 muriatic acid. Ibid. iv. 162. — Edit. 



