196 
CHEMISTEY OF HOETICULTUEE. 
100 disappeared; the mercury having gained so much , and undergone a complete altera- 
tion in its form and appearance, while 73 parts of a gas unfit for respiration (azote, then 
so called) remained unabsorbed. He reproduced these 27 parts, restored the metallic 
mercury, and therefore, proved that the 27 parts consisted of vital, respirable air (oxygen). 
He then mixed the two gases so as to produce a total of 1 00 parts, and found that an 
elastic fluid, precisely similar to atmospheric air, was the result ; and thus he effected 
what he deemed the synthetic proof of the composition of atmospheric air. 
Other chemists have subsequently arrived at rather different conclusions, concerning 
the proportions of the two prime constituents of air. Thus, Dr. Henry estimated them 
at 21 per cent, of oxygen gas, and 79 per cent, of nitrogen, both by measure — the 
difference evidently arising from the omission, by Lavoisier, of the carbonic acid and 
watery vapour. The late Samuel Parkes, an excellent practical chemist of the wholesale 
laboratory, agreed with Henry ; adding, that by weight, the two gases are as 23 of oxygen 
to 77 of nitrogen. He estimated the water or aqueous vapour at 100th, and the 
carbonic acid at 1000th part of the whole. 
Mr. Dalton’s analysis gave in the 100 parts — 
Oxygen Gas 21 -00 
Nitrogen Gas 77‘50 
Aqueous Yapour ......... 1.42 
Carbonic Acid .......... 0*08 
100-00 
Carbonic acid, formerly known as fixed air and aerial acid, was discovered in 1757, by 
Dr. Black, of Edinburgh. It is obtained in its purest state by the combustion of the 
diamond in oxygen gas, an experiment which has proved that the most costly of precious 
stones is simply charcoal in its most exalted condition, produced in the stupendous 
laboratory of Nature. Before entering upon any further inquiries, the reader should be 
told that carbonic acid however produced, suffers no increase of bulk above that of the 
oxygen gas, with which the required quantity of carbon combines. The ultimate 
atom or particle of carbon is six times heavier than that of hydrogen ; and as oxygen, 
as we have seen, is equivalent to 8, therefore, the combining proportions of the two, are 
represented by— 
Carbon 1 ~ 6 ) no 
Oxygen 2=16 J 
The experiment now to be described, is often exhibited in lecture-rooms. Charcoal 
is burned in a bell-glass of oxygen gas, and furnishes brilliant sparks in great profusion. 
If the charcoal be hard, well-burned, and made from a close, dense wood, the scintillations 
are not so striking and numerous, as when the tissue is lax and spongy ; it consumes with 
intense glowing heat, and gradually disappears, the product being carbonic acid in equal 
volume with that of the oxygen employed. Some years ago, an immense quantity of 
sesquicarbonate (commonly called Carbonate of Soda) was made by merely exposing 
crystals of soda in shallow canvas trays, to the action of the fume of burning charcoal. 
By degrees, the acid gas developed by the combustion, combined with the soda. The 
crystals discharged the bulk of the water which they contained, and were converted into 
opaque, cellular, and light masses of the sesquicarbonate. Lime combined with carbonic 
acid in the proportion of about nine of the former to seven of the latter, becomes chalk 
(Carbonate of Lime). Pure white marble is chalk in a granular or crystalline form. Let 
small fragments of that be introduced into a two-necked bottle, adding water sufficient to 
cover them : then, pour muriatic acid into a small glass funnel that has a long slender 
tube which passes half through the water, but not so far as to reach the fragments. 
Every drop will produce effervescence by combining with the lime of the marble, and 
releasing the aerial carbonic acid. This may be collected by passing it through a tube 
doubly bent, into an inverted glass jar, filled with water, and standing on the shelf of a 
pneumatic trough, and will thus be obtained in a state of great purity ; but as water slowly 
