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Historical Account of the Discovery of the Composition of Water. 

 By the Right Hon. Henry Lord Brougham, F. R. S., and 

 Member of the National Institute of France. 



There can be no doubt whatever that the experiment of Mr Warltire,* 

 related in Dr Priestley's 5th volume, gave rise to this inquiry, at least in 

 England; Mr Cavendish expressly refers to it, as having set him upon 

 making his experiments. — (Phil. Trans. 1784, p. 126.) The experiment 

 of Mr Warltire consisted in firing by electricity a mixture of inflammable 

 and common air in a close vessel, and two things were said to be ob- 

 served ; first, A sensible loss of weight ; second, A dewy deposit on the 

 sides of the vessel. 



Mr Watt, in a note to p. 332 of his paper, Phil. Trans. 1784, inadver- 

 tently states, that the dewy deposit was first observed by Mr Cavendish ; 



' Mr Warltire's letter is dated Birmingham, 18th April 1781, and was pub- 

 lished by Dr Priestley inithe Appendix to the 2d Vol. of his " Experiments and 

 Observations relating to various branches of Natural Philosophy ; with a conti- 

 nuation of the Observations on Air," — forming in fact the Sth volume of his " Ex- 

 periments and Observations on different kinds of Air," printed at Birmingham 

 in 1781. 



Mr Warltire's first experiments were made in a copper ball or flask, which 

 held three wine pints, the weight 14 oz.; and his object was to determine " whe- 

 ther heat is heavy or not." After stating his mode of mixing the airs, and of 

 adjusting the balance, he says he " always accurately balanced the flask of 

 common air, then found the difference of weight after the infl.immable air was 

 introduced, that he might be certain he had confined the proper proportion of 

 each. The electric spark having passed through them, the flask became hot 

 and was cooled by exposing it to the common air of the room: it was then hung 

 up again to the balance, and a loss of weight was always found, but not con- 

 stantly the same ; upon an average it was two grains." 



He goes on to say, " 1 have fired air in glass vessels, since I saw you (Dr 

 Priestley) venture to do it, and I have observed, as you did, that, though the 

 glass was clean and dry before, yet, after firing the air, it became dew.v, and was 

 lined with a sooty substance." 



As you are upon a nice balancing of claims, ought not Dr Priestley to have 

 the credit of first noticing the dew? 



In some remarks which follow by Dr Priestley, he confirms the loss of weight, 

 and adds, "■ I do not think, however, that so very bold an opinion, as that of the 

 latent heat of bodies contributing to their weight, should be received without 

 more experiments, and made upon a still larger scale. If it be confirmed, it 

 will no doubt be thought to be a fact of a very remarkable nature, and will do 

 the greatest honour to the sagacity of Mr Warltire. 1 must add, that the mo- 

 ment he saw the moisture on the inside of the close glass vessel in which I af- 

 terwards fired the inflammable air, he said, that it confirmed an opinion he had 

 long entertained, viz. that common air deposits its moisture when it is dephlo- 

 gibticated." 



It seems evident, that neither Mr Warltire, nor Dr Priestley, attributed the 

 dew to any thing else than a mechanical deposit of the moisture suspended in 

 common air.— (Notb bv Mr James Watt. ) • 



