CAR
CAR
( 86 )
that it became impossible to ascertain the .carbonconsumed.
7. Some of the animal charcoal was heatedto redness under sand for an hour, after which4 grains of it were put into the platina tube.On first passing the oxygen over it, flashes ranalong the glass tube, and the whole gas becamecloudy. The platina tube after the experimenthad lost 3.2 grains, but this loss was not whollycarbon, as some of the salts contained in theanimal charcoal might have been volatilized bythe heat, and in fact the inner surface cf tiregasometers was slightly covered with an efflo-rescence. To make this experiment agree withthe former ones, it is necessary to suppose halfa grain of volatile matter in thecharcoal.
The results of the above experiments, exclud-ing those on animal charcoal, gave the followingweight of .carbon in .100 carbonic acid.
0.2 grains of
Carbonic Acid.
28.9228.9528. S228.2028.46
28.77
28.81
28.72
28.27
28.46
The mean of the first column of numbers is28.67, and ol the second 28.60. The authorshowever mention with great candour, that twoexperiments with box-wood charcoal gave 29.75and 30.68 per cent, of carbon.; and one experi-ment with diamond gave 29.96, all of which arerejected from the mean estimate as being inac-curate.
The general inferences from these experimentsare, that 100. grains of carbonic acid containabout 28.6 grains of carbon: that well burntcharcoal contains no sensible quantity of hydro-gen, but if exposed to the air for a few minutes,it absorbs moisture, which renders the analysisin this state uncertain : and that charcoal cannotwith any propriety be considered as oxyd of dia-mond, since it requires full as much oxygen to heconverted into carbonic acid as diamond does.
We may add too that these experiments con-firm the fact first observed by Lavoisier , thatwhen oxygen gas is converted into carbonic acidby the combustion of charcoal, no change what-
ever tabes place in the volume of the gas, so thatin all analyses one measure of pure carbonic acidmay be safely assumed as indicating the samemeasure of oxygen gas.
The above experiments are valuable for theaccuracy with which they appear to have beenperformed, and the fidelity with which the re-sults are related, but two defects have beenpointed out. One of them is, that in no in-stance were any of the gasses stated to havebeen freed from hygrometric moisture, whichdelect is particularly to he noticed in the esti-mation of tne carbonic acid gas, since in theexperiment by which the weight of this gas wasfirst ascertained, it was procured in the moistway directly from marble and sulphuric acid ;but in the subsequent experiments the carbonicacid was formed by ignition of charcoal care-fully dried.
The other defect is, that all the gas after com-bustion was analyzed only by lime-water to ab-sorb the carbonic acid, and by nitrous gas insulphat of iron to remove the oxygen ; the re-sidue unabsorbed by either being assumed asazote without further examination. However,as this unabsorbed residue in every instancealmost exactly corresponded with the originalazotic impurity of the oxygen employed, thisomission is perhaps of less importance than dieother.
The next series of experiments on this sub-ject which we shall mention, are those ofTheodore de Saussure, ® which were conductedwith the express view of avoiding certainsources of error presumed in those just related.
The first object was to find the specific gravityof oxygen and carbonic acid. The author givesthe weight of a cubic decimetre (61.028 E.cub. inch.) of oxygen gas not freed from hygro-metric moisture to be 1.3552 grammes (20.88Eng . grains) at 12.5° cent, therm. (54.5°Fahr.)and at 0.758 metre pressure (29.843 Eng .inches.)
The weight of the same quantity of moistcarbonic acid gas under similar circumstances,is given at 1.8578 grammes (28.6918 Eng . grs.)When these are reduced to English weightsand measures, it will be found as follows:
grams.
100 cubic inches of undried oxygen at 30° Bar. and 60® Therm, weigh 34.003100 ditto of undried carbonic acid .... 46.727
These numbers, it maybe remarked by the way, M. Saussure performed the combustion of thesomewhat differ from those of Messrs. Allen carbonaceous substances in a tubulated receiverand Pepys , who give 33.82 grains for the oxy- of about 5 \ pints capacity, and ignited themgen, and 47.26 for the carbonic acid. by a burning lens. The charcoal was suspended
* Ana, Chim, tom. 7i.