THE NITRATE INDUSTRY

11

ty. The richer and more easily extracted nitrate, the first to be worked, is stated to be
ned to the valleys of the Tarapaca and Tacoma, and, it is asserted, will not last much longer
1923 at the present rate of increased extraction. 100-150 years is the limit assigned for the
ing out of the less valuable beds in the hands of the Government. However, it must be
mbered that perfectly enormous supplies of inferior nitrate remain in the soil, now regarded
>t worth working, and possibly with improved methods these supplies will last much longer
ttie estimated time. In fact, fresh estimates by competent scientists put off the date of failure
2 caliche beds for another 150 years at least.
LJses of Sodium Nitrate.—The main use of sodium nitrate is for manurial
>oses, no less than 80 per cent, of total product being used for this purpose in
2. Of the remaining 20 per cent used for manufacturing nitrogen com-
ids, about 15 per cent was used for making nitric acid, and the remaining
ir* cent for manufacture of potassium nitrate (saltpetre) for use in the lead
nber process for making sulphuric acid, and for other purposes as well
^or the manufacture of old black gunpowder or for fireworks, the slightly
•oscopic nature of NaNO3 renders it inapplicable as a substitute for potassium
Lte, KNO3.
POTASSIUM NITRATE, KNO3.
Potassium Nitrate, KNO3, crystallises in large prisms, isomorphous with
n"foic aragonite, and so is sometimes known as "prismatic" saltpetre. It is
. principally for the production of black shooting powder and for fireworks.
HEowever, since the production of the new smokeless powders, the manufacture
lack powder has greatly decreased, and with it the use of potassium nitrate
il so decreased.
^Canufacture.—Germany alone produces 20,000 tons of KNO3, and Great
tin imports annually 10,000 tons, while over 30,000 tons are produced in other
3, almost entirely by the so-called "conversion process," using as raw materials
German potassium chloride, KC1 (mined at Stassfurt) and Chile saltpetre,
irn nitrate, NaN03. This process depends upon the fact that under certain
Litions of temperature and pressure, solutions of potassium chloride, KG, and
s saltpetre, NaN03, when mixed, undergo a double decomposition, sodium
ride being deposited and potassium nitrate remaining in solution :—
KC1 -1- NaNO:J = NaCl + KNO:5.
conversion takes place all the more readily because KNO3 is much more
:>le in hot and much less soluble in cold water than is sodium nitrate. 100 g.
iter dissolve:—
KNOy. NaNCXj. NaCI. KC1.
At 20° C. 32 g. 88 g. 36 g. 34 g.
,,ioo°C. 246 g. 176 g. 39.6 g. 56.5 g.
potassium nitrate thus obtained is exceedingly pure. In fact, that technically
uced for the manufacture of black powder must not contain more than 0.1-0.05
rent. NaCl.
?tie process is carried out as follows :—In a large iron pan, provided with a
ng apparatus and indirect steam heating arrangement, there is added 188 kg.
ssium chloride (88 per cent., containing- NaCl) and 180 kg. Chile saltpetre
per cent) and 160 kg. of mother liquors from a previous operation. The
ion is boiled by indirect steam. The amount of water present is not
rient to dissolve all the difficult soluble NaCl present, whereas the readily
>le KNO3 at once goes into solution. The liquid is filtered hot, and the
u.al salt, after covering with a little water, and draining, is sold as such. The
11 other liquors are allowed to cool, when "raw" KNO3 crystallises out—still in
tele state, however, containing several per cent, of NaCl.
^tie crude KNO3 is once more dissolved by hot water, and allowed to crystallise
opper pans provided with stirrers. " Refined" potassium nitrate is thus