Description of a Manometer. 461 



by tbe liquid contained in the apparatus, may be determined 

 by precipitating this acid by lime water, or by water of 

 barytes, either from the whole or from a part of the liquid : 

 after that, we introduce the precipitate into a flask, adapt the 

 tube of a funnel to it, through which we pour a quantity of 

 dilute sulphuric acid ; and by the loss of weight which takes 

 place, we ascertain the quantity of carbonic acid which was 

 dissolved in the liquid, and which is disengaged from the 

 carbonate. — We may, by the processes which I have indi- 

 cated, ascertain in a volume of air equal to that of a kilo- 

 gramme of water, and contained in a manometer which has 

 this dimension, the change which would be produced by 

 the volume of one gramme of water ; the production of a 

 quantity of carbonic acid which does not exceed a centi- 

 gramme in weight; and a variation in the proportions of the 

 oxygen and azote which does not exceed a centieme : this 

 is a precision which would seem to be sufficient for all the 

 determinations which we would wish to establish. 



We have besides the advantage of being able to repeat 

 and compare the tests at different times, without in- 

 terrupting the experiment, and to vary several of its cir- 

 cumstances: 1 have constructed manometers of different 

 dimensions, in order to apply them to different objects^ 



Hitherto I have made but a small number of observations 

 with this instrument, and I have not pursued them with 

 the care which they require; but my chief object in this 

 publication is to induce those to employ it who are occupied 

 with experiments of this nature, and who have more leisure 

 and perseverance than I have. I shall describe some early 

 attempts. 



M.Theodore de Saussure, to whom we are indebted for 

 some learned and laborious researches upon vegetation, has 

 shown, that in most of the cases where we suppose thai the 

 oxygen gas was absorbed by a vegetable or animal substance, 

 there is simply formed a combination of the, carbon of 

 these substances with the oxygen of the atmosphere; that 

 the volume of the gas did not diminish, except on account 

 of the absorption of the carbonic acid by water; and that 

 at the same time water was produced by the combination 

 of the oxygen and hydrogen which existed in the sub- 

 stance ; so that, although the residue had been deprived of a 

 part of its carbon by the action of the oxygen £>as, it is 

 nevertheless found more carbonized afterwards, because it 

 has been stripped of a greater proportion of hydrogen and 

 oxygen than of carbon*. 



* Reiherches Chimiques sur la rjgjtatidn. 



It 



