120 POTASH-MAKING IN ESSEX : A LOST RURAL INDUSTRY.
Essay III.—Of Saline Substances (Vol. i., pp. 130-135. ". . . The ashes
of most other vegetables, as well as those of maritime plants, yield a salt which
has many properties in common with the mineral fixed alkali ; but not having
all the properties of that salt, it has for the sake of perspicuity been called the
vegetable fixed alkali. Both the mineral and the vegetable fixed alkali are prepared
by boiling the ashes, to extract the salt from the earth ; the water containing the
salt in solution is then evaporated so as to leave the salt dry. From this manner
of preparing them, these salts have been often called lixivial salts, lix and lixivium
both signifying a ley made with ashes. The operation of evaporating the water
is performed in large iron or copper pots ; and from this circumstance these alkaline
salts, especially the vegetable fixed alkali, have come under the name of pot-ash.
" Great piles of wood are, in many countries, burnt for the express purpose of
obtaining pot-ash. From the following experiments, some notion may be formed
of the large quantities of wood which must be burned in order to obtain even a
small portion of pot-ash.
" I desired a friend in Essex, who had plenty of dry oak billets, to ascertain the
quantity of ashes which a certain weight of the wood would yield. He made the
experiment with every possible precaution, and from 106 pounds, avoirdupois
weight, of dry peeled oak, he obtained 19 ounces of ashes. I treated these ashes
after the same manner in which I had endeavoured to ascertain the proportion of
earth and saline matter in barilla, and kelp ashes ; and from the 19 ounces ob-
tained rather more than one ounce and a quarter of saline matter. From several
repetitions of the experiment with ashes of the same kind it may be concluded that
15 ounces of these ashes contained 14 ounces of earth, not soluble in water, and
one ounce of saline matter : from this proportion it may be easily collected [Sic,
probably a slip for 'calculated.'—J. S.] that above 1,300 tons of dry oak, and
probably above 1,800 tons of green oak, must be burned in order to obtain one
ton of pot-ash.
" The makers of pot-ash generally buy the wood ashes by the bushel, and sell
the pot-ash by the ton ; but as the ashes out of different woods, and indeed of
different parts of the same wood, probably contain very different portions of saline
matter, it cannot be expected that we should have any very uniform accounts of the
number of bushels of ashes requisite to make a ton of pot-ash. Some dealers in
this article are . of opinion that a ton of pot-ash may be procured from 460
bushels of ashes; others, from 450 ; others, from 560 of the best ashes ; and
others, lastly, from 700 bushels, at a medium, of good and bad ashes.1 I find that
a bushel of the dry ashes, which are sold by the country people who burn wood to
our soap-makers in Cambridge, weighs at a medium 58 lbs. ; hence, supposing
every 15 lbs. of such ashes to contain 1 lb. of saline matter, it will follow that 580
bushels of such ashes would give one ton of saline matter. This correspondence
with the accounts given by the pot-ash makers, confirms the analysis of the oak
ashes before-mentioned.
" Under the direction and patronage of the Society for the Encouragement of
Arts, Manufactures, and Commerce, large quantities of pot-ash have been made in
America since the year 1763 ; and it would be a great saving to the nation if it
could be made in sufficient quantities in any part of the dominions of Great
Britain, since we are reckoned to pay to Russia, and other sovereign states, not less
than £150,000 a year fol pot-ash."2]
1 Lewis's "Experiments on American Potash," p. 6.
2 Dossie's "Mem. of Agriculture," vol. i., p. 248.