VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. qq 



venience, the fixed air was made to unite with calcareous earth, by pouring into the 

 alkaline solution a sufficient quantity of a saturated solution of marble in marine 

 acid. The vessel which contained them being closed, was left undisturbed till the 

 precipitate had fallen to the bottom, the solution having been previously heated that 

 it might subside more perfectly. The clear liquor being found, by means of lime- 

 water, to be quite free from fixed air, was carefully poured off from the calcareous 

 precipitate.* The vessel used on this occasion was a glass globe, having a tube 

 annexed to it, that the quantity of the fixed air might be more accurately measured. 

 After as much quicksilver had been poured into the glass globe containing the cal- 

 careous precipitate as was necessary to fill it, it was inverted in a vessel of the same 

 fluid. Some marine acid being then made to pass up into it, the fixed air was ex- 

 pelled from the calcareous earth ; and in this experiment, in which 2-±- grs. of dia- 

 monds had been employed, occupied the space of a little more than 10.1 oz. of 

 water. The temperature of the room when the air was measured, was at 55°, and 

 the barometer stood at about 29.8 inches. 



From another experiment made in a similar manner with 1 gr. and a half of dia- 

 monds, the air obtained occupied the space of 6.18 oz. of water, according to which 

 proportion the bulk of the fixed air from 2 and 4- gr. would have been equal to 

 10.3 oz. 



The quantity of fixed air thus produced by the diamond, does not differ much 

 from that which, according to M. Lavoisier, might be obtained from an equal 

 weight of charcoal. In the Memoirs of the French Academy of Sciences for the 

 year 1781, he has related the various experiments which he made to ascertain the 

 proportion of charcoal and oxygen in fixed air. From those which he considered as 

 most accurate, he concluded that 100 parts of fixed air contain nearly 28 parts of 

 charcoal and 72 of oxygen. He estimates the weight of a cubic inch of fixed air 

 under the pressure and in the temperature above-mentioned, to be .695 parts of a 

 grain. If we reduce the French weights and measures to English, and then com- 

 pute how much fixed air, according to this proportion, 24- grs. of charcoal would 

 produce, we shall find that it ought to occupy very' nearly the bulk of 10 oz. of 

 water. 



M. Lavoisier seems to have thought that the aerial fluid produced by the com- 

 bustion of the diamond was not so soluble in water as that procured from calcareous 

 substances. From its resemblance however, in various properties, hardly any doubt 

 could remain that it consisted of the same ingredients ; and I found, on combining 

 it with lime, and exposing it to heat with phosphorus, that it afforded charcoal in 

 the same manner as any other calcareous substance. 



* If much water had remained, a considerable portion of the fixed air would have been absorbed by it. 

 But by the same method as that described above, 1 observed, that as much fixed air might be obtained 

 from a solution of mineral alkali, as by adding an acid to an equal quantity of the same kind of alkali.— 

 Orig. 



O 2 



