226 PHILOSOPHICAL TRANSACTIONS. [aNNO IJQ'l. 



tubes, under similar circumstances to those in the above experiment; and I found 

 that no carbonic acid, but a little water, came over into the air-apparatus; that 

 the total weight of the alkali was diminished, but that a given weight of it, after 

 the experiment, afforded rather more carbonic acid, by solution in acetous acid, 

 than an equal weight of the same parcel of alkali not thus subjected to heat. 

 This diminution of weight of alkali, and greater proportion of carbonic acid, I 

 impute to the water visibly separated in the glass tubes, and perhaps also absorbed 

 in the earthen ones. Accident afforded a still more decisive proof of the decom- 

 position of carbonic acid. In the beginning of the experiment, the tubes some- 

 times cracked about 4 or 5 inches from the part containing the phosphorus: on 

 cooling I found, in the part below the crack, black alkaline matter, which yielded 

 much less carbonic acid than the same weight of alkali before the experiment; 

 whereas the alkali above the crack was white, and contained the same quantity of 

 this elastic fluid that it did before it was exposed to heat. 



In the experiment above particularly described, it appears that in one part of 

 the alkali there was a deficiency of 20 oz. measures of carbonic acid per cent, of 

 alkali; but a production of rather more than 8 gr. of charcoal, and of as much 

 phosphoric acid as formed about 30 gr. of phosphoric selenite; the composition 

 of which may be estimated to be, of phosphorus, 5 gr.; respirable air, 10 gr.; 

 and quick-lime, 15 gr. Now, as it has been demonstrated by M. Lavoisier, 

 that charcoal, either totally, or a minute proportion excepted, combines with 

 respirable air, and forms carbonic acid; and other familiarly known, though less 

 accurate, experiments, show that carbonic acid is formed whenever charcoal and 

 respirable air are applied to each other in a due degree of heat; and as there are 

 no other sources perceivable of respirable air and charcoal in this experiment, it 

 seems to prove decisively that they are derived from the carbonic acid, which is 

 decompounded by the superior affinities between phosphorus and respirable air, 

 and phosphoric acid and alkali, to those between respirable air and charcoal, and 

 carbonic acid and alkali. An additional proof of the reality of this decomposi- 

 tion is afforded by the examination of the 358 gr. of white and grey alkaline 

 matter, of the same experiment, which affx)rded much more carbonic acid, and 

 much less charcoal and phosphoric acid. I am fully aware that the proportions 

 of respirable air and charcoal, produced in this experiment, do not correspond 

 to the proportions of them we should have expected, consistently with the syn- 

 thetical experiments concerning carbonic acid. The variation is especially great 

 with respect to respirable air, of which there should have been 18 gr. instead of 

 5, to combine with the whole of the charcoal, but, from the nature of the ex- 

 periment, we cannot even approximate to the truth with respect to the real quan- 

 tity of respirable air produced; for the phosphorus which sublimed probably car- 

 ried off' a little of this air, some of the phosphoric acid thus formed fused along 



