462 Description of a Manometer. 



It appeared to me to be useful to examine whether these 

 results, which give the explanation of several transmutations 

 undergone by animal and vegetable substances, might con- 

 duce to general consequences, or if they ought to be re- 

 stricted to a certain class of phenomena. 



M.de Saussure had already remarked that the oxvgen gas 

 was absorbed by the oils, without forming a corresponding 

 quantity of carbonic acid. 



The theory of the solution of indigo by the alkaline bases 

 which are combined with it, when it is deprived of Oxygen, 

 and of its precipitation by the oxygen of the atmosphere, 

 which has been explained in the Elements of the Art of 

 Dyeing, seemed established on sufficient proofs. Neverthe- 

 less the analogy, with the facts observed by M. deSaussure, 

 might lead us to believe that the oxygen of the atmosphere 

 served to form carbonic acid, with a part of the carbon of 

 the indigo which had been rendered soluble. 



A solution of indigo, made by means of the sulphate of 

 iron and of lime, limpid and of a fawn-colour, after having 

 been carefully separaied from the sediment, was introduced 

 into a manometer of 11 litres 632 capacity: the barometer 

 was at u m ,75.74, the thermometer at 12°: two days after- 

 wards the liquor was completely colourless, and the indigo 

 was precipitated in dark blue, the thermometer beingat 12,5, 

 the haromcier had fallen six millimetres. 



The filtered liquor was covered while in the air with pel- 

 Jicles of carbonateof lime, and precipitated abundantly with 

 oxalate of ammonia : the blue precipitate retained or, a filter 

 did not effervesce with an acid, and gave with sulphuric 

 acid a very deep solution of indigo. 



Thus we see that the lime preserved its state during: the 

 precipitation of the indigo, and that carbonic acid is not 

 formed. 



On the other hand, the test of the air contained in the 

 manometer has shown that it was the oxygen gas which 

 alone had been absorbed bv the indigo, whose precipitation 

 it had operated. The experiment repeated a second time 

 gave similar results: but we bete neglect the calculations 

 necessary for determining the quantity of the absorption, 

 because we have not ascertained the weight of the indigo 

 precipitated. We confine ourselves to the conclusion, that 

 the quantity of oxygen which disappeared has not been 

 employed in this case to form carbonic acid ; but that it is 

 combined with the indigo, to which it lias theieby rendered 

 its insolubility and colour. 



i was anxious to compare the changes which are pro- 

 duced 



