Lord Brougham on the Coiiiposilion of Water. 321 



ply Inflammable air, and he inclines rather to call inflammable air, water 

 united to phlogiston. Mr Watt says expressly, even in his later paper 

 (of November 1783), and in a passage not to be found in the letter of 

 April 1783, that he thinks that inflammable air contains a small quantity 

 of water and much elementary heat. It must be admitted that such ex- 

 pressions as these on the part of both of those great men, betoken a certain 

 hesitation respecting the theory of the composition of water. If they had 

 ever formed to themselves the idea, that water is a compovmd of the two 

 gases deprived of their latent heat, — that is, of the two gases, with the 

 same distinctiveness which marks Mr Lavoisier's statement of the theory 

 such obscurity and uncertainty would have been avoided.* 



Several further propositions may now be stated, as the result of the 

 facts regarding Mr Watt. 



First, That there is no evidence of any person having reduced the 

 theory of composition to writing, in a shape which now remains, so early 

 as Mr Watt. 



Secondly, That he states the theory, both in April and November 1783, 

 in language somewhat more distinctly referring to composition, than Mr 



• Mr Watt, in his letter of •26th April 1783, thus expresses his theory and con- 

 clusions (Phil. Trans, p. 333) : " Let us now consider what obviously happens in 

 the case of the deflagration of the inflammable and dephlogisticated air. These 

 two kinds of air unite with violence, they become red hot, and, upon cooling, 

 totally disappear. When the vessel is cooled, a quantity of water is found in it, 

 equal to the weight of the air employed. This water is then the only remain- 

 ing product of the process, and water, light, and heat, are all the products" (un- 

 less, he adds in the paper of November, there be some other matter set free, 

 which escapes our senses). " Are we not then authorized to conclude, that water 

 is composed of dephlogisticated air and phlogiston, deprived of their latent or ele- 

 mentary heat ; that dephlogisticated or pure air is composed of water deprived of 

 its phlogiston, and united to elementary heat and light; that the latter are con- 

 taitied in it in a latent state, so as not to be sensible to the thermometer or to the 

 eye ; and if light be only a modification of heat or a circumstance attending it, or 

 a component part of the inflammable air, then pure or dephlogisticated air is com- 

 posed of water deprived of its phlogiston and united to elementary heal V 



Is this not as clear, precise, and intelligible, as the conclusions of Mr Lavoi- 

 sier ? — [Note by Mr James Watt.] 



The obscurity with which Lord Brougham charges the theoretical conceptions 

 of Watt and Cavendish does not appear to me well founded. In 1784, the pre- 

 paration of two permanent and very dissimilar gases was known. Some called 

 these gases, pure air and inflammable air ; others, dephlogisticated air and phlo- 

 giston ; and lastly, others, oxygen and hydrogen. By combining dephlogisti- 

 cated air and phlogiston, water was produced equal in weight to that of the two 

 gases. Water thenceforward was no longer a simple body, but a compound of 

 dephlogisticated air and of phlogiston. The chemist who drew that conclusion, 

 might have erroneous ideas as to the intimate nature of phlogiston, without 

 throwing any uncertainty upon the merit of his first discovery. Even at this 

 day, have we mathematically demonstrated, that hydrogen (or phlogiston) is an 

 elementary body ; or that it is not, as Watt and Cavendish supposed at the time, 

 the combination of a radical and of a little water .' [Notb by M. Arago. ] 



