24 On the Manufacture of Saltpetre. [JAN 
a large mud filter, lined on the inside with stiff clay. Itisa round 
hollow basin, in shape resembling the top of a well, from 6 to 8 inches 
in diameter. A false bottom is formed of pieces of bamboo, laid close, 
and resting upon pieces of brick. This leaves an empty space of a few 
inches above the solid bottom, for an outlet to the filtered liquor. Over 
these bambis, a covering of strong close wrought grass mats are laid, 
which complete this simple form of filter. The operation then proceeds 
with the process, by spreading over the mats a thin layer of vegetable 
ashes, generally from the indigo plant, upon which the earth to be sub- 
jected to the filtering process is laid, and trodden down level, and to 
the desired solidity, by the operator’s feet. This requires great atten- 
tion on the part of the man who performs it: for if too solid, the water 
will pass through too slow; on the contrary, if too soft, the water will 
pass through too quick; for the solution of the saline matter to take place, 
and the full products would not be obtained. After this point has been 
adjusted, water is poured gently upon the earth to the depth of four or 
five inches, according to the size of the filter and quantity of earth 
used, (one of six feet diameter will filter 20 maunds of earth.) The 
whole is then suffered to remain tranquil for several hours, during which 
time the water gradually passes through the earth, dissolving the saline 
matter in its passage, and filtering through the mats, drops into the 
empty space between the solid and false bottoms, and is conveyed by 
means of a spout of bambi, or a hollow tile, into an earthen receiver, 
made large enough to hold the full quantity of filtered liquor, and half 
sunk in the ground for the purpose. 
The saltpetre liquor thus obtained is more or less coloured with oxide 
of iron and decomposed vegetable matter. Its specific gravity also 
varies with the quality of the earth operated upon. An average from 
a great number of filters gave me 1.120. 
The second process is to evaporate the saltpetre liquor to a crystal- 
_lizing state, which is effected in earthen pots fixed in two rows, over 
an oblong cavity dug in the ground, the interstices between the post 
being filled up with clay. An aperture at one end of the cavity serves 
for an egress to the smoke; another at the opposite end is used for the 
introduction of fuel, which is generally dry fallen leaves gathered from 
the dm topes (mango groves): such are the simple materials used in 
this part of the manufacture. The boiling is continued till the liquor is 
evaporated to the crystallizing point, which is ascertained by the opera- 
tor taking from time to time a small portion of the liquor from the 
pots, and setting it aside to cool in small earthen dishes, like a common 
saucer. After the liquor has cooled, and the crystals formed agreeable 
