Description of a Manometer. 46*3 



duced by a colouring substance of a different species, which 

 was cam peachy wood. 



The decoction of campeachy generally obtained has a 

 blue colour, because we prepare it in copper vessels: jt is 

 of a fine red when glass or silver vessels are used. 



This very clear decoction was cooled in a bottle with a 

 ground stopper, in order that it might not be altered by the 

 contact of the air, and placed in the manometer, the ther- 

 mometer being at 18,5, the barometer O m .7593: four days 

 afterwards the liquor was turbid, and the temperature being 

 the same, the interior barometer fell () m .03. This lowering 

 continued for two months, and in this time the liquor beeame 

 very turbid and of a reddish fawn colour: a trifling sedi- 

 ment was formed, and some crusts. 



At the end of the experiment the thermometer was 21 ,25, 

 the total lowering of the barometer O m .05(), the air of the 

 manometer wheif referred to its primitive pressure contained 

 in 100 parts 



Carbonic acid , . . 3 oi 



Oxygen 6'55 



Azote . 89*54 



There was at. the end of the operation an increase of tem- 

 perature of 3° 25, which requires the following correction 

 in the volume of the gas at the primitive pressure of 

 ,n .7593. 



According to the determinations which M. Gay-Lussac 

 communicates, the quantity by which a volume of air is di- 

 lated by 1°, is expressed by the height of the barometer 

 which represents the tension of this air divided by 266,66, 

 and becomes on setting out from the degree above zero equal 

 to the quotient of the tension by this divisor, augmented 

 by the number of degrees from which we begin to count 

 the dilatation. In the present case, the height of the baro- 

 meter at the commencement of the operation = 0'".7593, 

 the temperature 18°, the column of mercury corresponding 

 to a dilatation of 1° will therefore be 



£ ■»#»» = 0^.00266, 

 26660+18 



and that which is to take off for the dilatation is 3°. 25 = 



0,00864. * . . 



As to the vapour which ought to be formed on bringing 



the numbers of the table of Dalton to the degrees of the 



centigrade thermometer, and to the divisions or the metre, 



we find that the tension of the vapour being 21°,25, 



= O m .018J7 — 



and at 18° = cr .01536. The 



