16 
GLEANINGS IN SCIENCE. 
Probably the atmospherical air of the apparatus, as well as that contained m 
the water, and that which remained entangled among the leaves, tnav account m 
some measure for the presence of the oxygen and azote in the first analysts ; but 
the large proportion of azote, especially in the second experiment, so much sur- 
passes >vhat might be expected from this source alone, that it seems necessary to 
attribute it, in part at least, to an emission from the leaves during the fermenta. 
tion ; nr probably the leaves, still retaining atmospheric air on their absorbent 
surfaces, convert the oxygen thereof into carbonic acid, and allow the azote to 
escape. After the disengagement has ceased, it will he seen by the next expeii- 
nient that the proportion of azote decreases very much. Some of the fermented 
liquid of a large vat was well boiled, and the gas collected over water : on ana- 
lysis, it proved to be composed of 
Carbonic Acid, ... 78- 
Oxygen, 2.3 
Azote, 10.7 
100 . 
And in a second experiment, conducted with greater care to exclude external 
air, the result was 86 per cent, of carbonic acid, and the residue contained too 
feeble a portion of oxygen to explode with the electric spark on the addition of a 
requisite proportion of hydrogen. 
In no case, therefore, does the extricated gas in practice appear to he pure carbo- 
nic acid ; but from tbe prevalence of the latter increasing with the precautions 
taken to exclude common air, it may in fact be the only gas strictly due to the 
fermentation properly so called, the remainder of common air ha iiig been sus- 
pended in contact with the leaves, and being deprived of a portion of its oxygen- 
by the free carbon, or by tbe liquid in its passage to the surface. No carburetted 
hydrogen or other combustible gas w as found among the gaseous products 
The Indigo manufacturer does not wait until the. extrication of gas is con- 
cluded, but w ithdraws the liquid from the steeping vat as soon as he considers it to 
he sufficiently fermented ; judging either from the smell, from the greenish tint of 
the liquor on the surface, or from the formation of an irridettcent scum on tbe 
hubbies of gas. In fact when the liquid, which is of itself of a bright vellow 
colour, begins to assume a greenish tint, it is evidently caused by an incipient 
precipitation of the blue colouring matter i and it would he attended with a loss 
of produce, to allow* this precipitation to take place in the steeping vat among 
the leaves and branches of the plant. B ® 
“ The length of the fermentation depends upon the temperaiure, the weather • 
the w ind, the water employed, and the ripeness of the plant ; it may last in com- 
mon cases from seven to fifteen hours. It is generally longer when the tem- 
perature is high, the w eather cloudy, but not rainy ; the wind eastward and 
moderate, the plant npe and fresh.” 
th f B several points, constant experience leaves little for the experimen- 
talist to advance ; but it may he remarked, that almost all the criteria of a good 
fermentation, as far as the weather is concerned, concur in one simple ml 
pie, -the prevention of the water of the vat from being cooled; for the X 
w,nd, being dry, cools it by evaporation ;_s,rong wind does tlie 4me eTew 
sky cools it by rad.atmn ; and rain, by the low temparature of rain wm ”r ’~r w 
mometers placed in the vats did not present any satisfactory result " fh 
temperature was about 85 degrees Farenheit. " y esu t » l * le mean 
« heating v™ 1 ** ^ ,lrai “ e, > inferior «*•, which are called the 
At the time when the vat is opened, the liquid is found hr, • 
a specific gravity (at the surface) of 1001.5 • and ar thl to tave 
1003.1. The leaves appear to hive lost notWpg, b * J 
when they were first strewed in the vat. Uy carefull v weiX* " d ™ sh a r 
leaves, however, before immersion, and washing and drvrn^Th^ ^ P orMon of 
it they were found to have lost more than thfee qua«ers & '• I ' f af,er f 
tins loss the greater part was water, which they Lparentlv ' we, g ht ° f 
power* of retaining when the soluble inioes have - , c<iase to have the 
matter taken up by the vat ^ount to betw^II and Hner^T"/ 7 he ^ 
Ot the leaves. * dlia per cent, fo the weight 
