=210. Functions of Sodium Nitrate.=—Practically the only form of
oxidized nitrogen which is of importance from an agronomic point of
view is sodium nitrate, often known in commerce by the name Chile
saltpeter. Applied to a growing crop it at once becomes dissolved at
the first rainfall or by the natural moisture of the soil. It carries
thus to the rootlets of plants a supply of nitrogen in the most highly
available state. There is perhaps no other kind of plant food which
is offered to the living vegetable in a more completely predigested
state, and none to which a quicker response will be given. By reason
of its high availability, however, it must be used with care. A too
free use of such a stimulating food may have, in the end, an injurious
effect upon the crop, and is quite certain to lead to the waste of a
considerable portion of expensive material. For this reason sodium
nitrate should be applied with extreme care, in small quantities at
a time and only when it is needed by the growing crop. It would be
useless, for instance, to apply this fertilizer in the autumn with
the expectation of its benefitting the crop to a maximum degree the
following spring. Again, if the application of this salt should be made
just previous to a heavy rain almost or quite the whole of it would be
removed beyond the reach of the absorbing organs of the plant.
When once the nitric acid has been absorbed by the living rootlet it
is held with great tenacity. Living plants macerated in water give up
only a trace of nitric acid, but if they be previously killed with
chloroform the nitric acid they contain is easily leached out.
The molecule of sodium nitrate is decomposed in the process of the
absorption of the nitric acid. The acid enters the plant organism and
the soda is excreted and left to combine with the soil acids. The
nascent soda may thus play a role of some importance in decomposing
particles of minerals containing potash or phosphoric acid. It is
probable that the decomposition of the sodium nitrate takes place
in the cells of the absorbing plant organs for it is difficult to
understand how it could be accomplished externally. While the soda
therefore is of no importance as a direct plant food it can hardly be
dismissed as of no value whatever in the process of fertilization.
Many of the salts of soda as, for instance, common salt, are quite
hygroscopic and serve to attract moisture from the air and thus become
carriers of water between the plant and the air in seasons of drought;
and sodium nitrate itself is so hygroscopic as not to be suited to the
manufacture of gunpowder.
To recapitulate: The chief functions of sodium nitrate are to give
to the plant a supply of oxidized nitrogen ready for absorption into
its tissues and incidentally to aid, by the residual soda, in the
decomposition of silt particles containing potash or phosphoric acid
and in supplying to the soil salts of a more or less deliquescent
nature.
=211. Commercial Forms of Chile Saltpeter.=—The Chile saltpeter of
commerce may reach the farmer or analyst in the lumpy state in which
it is shipped or as finely ground and ready for application to the
fields. Unless the farmer is provided with means for grinding, the
latter condition is much to be preferred. It permits of a more even
distribution of the salt and thus encourages economy in its use. For
the chemist also it is advantageous to have the finely ground material,
which condition permits more easily a perfect sampling, a process
which, with the unground salt, is attended with no little difficulty.
=212. Percentage of Nitrogen in Chile Saltpeter.=—Chemically pure
sodium nitrate contains 16.49 per cent of nitrogen. The salt of
commerce is never pure. It contains moisture, potash, magnesia, lime,
sulfur, chlorin, iodin, silica and insoluble materials, and traces of
other bodies. The value of the salt depends, therefore, not only on the
market value of nitrogen at the time of sale, but also on its content
of nitrogen. The nitrate of commerce varies greatly in its nitrogen
content and is sold on a guaranty of its purity. The best grades
range in nitrogen from fifteen to sixteen per cent. The content of
nitrogen has long been estimated in the trade by determining the other
constituents and counting the rest as nitrogen. This practice arose
in former times when no convenient method was at hand for determining
nitric nitrogen. The process is tiresome and unreliable because all
errors of every kind are accumulated in the nitrogen content, but
inasmuch as the method is still required by many merchants, the analyst
should be acquainted with it, and it is therefore given further along.
The usual methods for determining nitric nitrogen may be applied in all
cases where samples of sodium nitrate are under examination, but some
special processes are added for convenience.
=213. Adulteration of Chile Saltpeter.=—The analyst is the only
protector of the farmer in guarding against the practice of
adulteration of sodium nitrate aside from the honesty of the dealer.
Even the honest dealer is compelled to protect himself against fraud,
and therefore, the world over, commerce in this fertilizer is now
conducted solely on the analyst’s certificate. Happily, therefore,
adulteration is almost unknown because it is certain to be detected.
Formerly, the saltpeter was adulterated with common salt, or low grade
salts from the potash mines; but it is an extremely rare thing now to
find any impurities in the salts other than those naturally present.
In every case the analyst may grow suspicious when he finds the content
of nitrogen in a sample to fall below thirteen per cent. It must not be
forgotten, however, that some potassium nitrate may be present in the
sample, and since that salt contains only 13.87 per cent of nitrogen
its presence would tend to lower the value of the fertilizer; but
although the potash itself is a fertilizer of value it is not worth
more than one-third as much as nitrogen. In all cases of suspected
adulteration, it is advisable to make a complete analysis. The results
of this work will, as a rule, lead the analyst to a correct judgment.
[Illustration: FIGURE 15. HALLE NITRIC ACID APPARATUS.]
=214. The Halle Zinc-Iron Method.=—For determining the nitrogen in
Chile saltpeter the reduction method is conducted at the Halle Station
as follows:[179] Ten grams of the nitrate are dissolved in one liter
and fifty cubic centimeters of the solution corresponding to half
a gram of the sample, taken for each determination. The apparatus
employed is shown in Fig. 15. A mixture of five grams of zinc dust
and an equal weight of iron filings is employed as the source of
hydrogen. The reduction takes place in an alkaline medium secured by
adding to the other materials mentioned, eighty cubic centimeters of
soda-lye of 1.30 specific gravity. The respective quantities of iron
and zinc may be measured instead of weighed, as exact proportions are
not required. After the addition of all the materials the flask is
allowed to stand for an hour at room temperature. The distillation
is then commenced and continued until at least 100 cubic centimeters
of distillate have been collected. The receiving flasks are ordinary
erlenmeyers, each of which contains twenty cubic centimeters of set
sulfuric acid, as in the usual kjeldahl process. The flasks are sealed
with a few drops of water by the device shown in the figure. After the
end of the operation the water in each one is washed back into its
proper flask with freshly boiled water. During the vigorous evolution
of hydrogen, at the beginning of the operation, some kind of a safety
arrangement is necessary to prevent the particles of soda-lye being
carried over by the bubbles of that gas. The siphon bulb shown in the
figure is found effective for this purpose. In this operation better
results are obtained by condensing the escaping steam, and for this
reason the block tin tubes are conducted through a tank supplied with
a current of cold water. The ends of the tubes should not dip below
the surface of the liquid in the receivers. When the condensed liquid
collects in considerable quantities in the safety tube the lamp should
be extinguished under the flask, which permits the return of the liquid
to the flask by means of the siphon. This should be done two or three
times during the progress of the distillation to prevent a too high
concentration of the soda-lye, thus endangering the flask. The excess
of the acid in the receiver is determined by titration, as in the
regular kjeldahl method. Blank determinations should be made, from time
to time, and corrections made in harmony therewith.
=215. Method of the French Sugar Chemists.=—The nitrogen in Chile
saltpeter is estimated by the French chemists according to the method
of Schlösing, described in the first volume, page 500. In order to
avoid the trouble of calculating the results from the volume of nitric
oxid obtained, a determination is first made with a pure salt, sodium
or potassium nitrate. The volume of gas obtained is read directly
without correction and taken for direct comparison. The comparison is
made as follows:
The solutions of the pure salts and of the sample to be analyzed
are made of such a strength as to contain sixty-six grams of sodium
nitrate, or eighty grams of potassium nitrate, in a liter. Five cubic
centimeters of such a solution will yield a little less than 100 cubic
centimeters of nitric oxid under usual conditions. Let the volume of
gas obtained with the pure salt be _v_; and that with the sample be
_v′_. The calculation is then made from the equation:
_v′_ _x_
---- = ----.
_v_ 100
_Example_: Let ninety-five cubic centimeters be the volume of
gas from five cubic centimeters of the pure salt (sodium nitrate),
and 91.5 cubic centimeters be the volume of gas from five cubic
centimeters of the sample; then
91.5 _x_
---- = ----, whence _x_ = 96.31.
95 100
Hence the sample analyzed contains 96.31 per cent of sodium
nitrate. Since the pure sodium nitrate contains 16.47 per cent of
nitrogen the sample under examination would contain
16.47 × 96.31
------------- = 15.86 per cent.
100
It is evident that this comparative method is quite easy of application
when the sample under examination has no other nitrate in it except
that combined with the one base.
=216. Volumetric Method of Gantter.=—The process proposed by Gantter
for determining the nitrogen, volumetrically, in Chile saltpeter and
other nitrates is based on the following principles:[180]
(1) If a nitrate be heated in contact with sulfuric and phosphorous
acids, nitrous acid will be formed.
(2) If nitrous acid be boiled with ammonium chlorid, nitrogen will
be quantitatively evolved from both compounds. These processes are
illustrated by the following formulas:
(a) N₂O₅ + P₂O₃ = N₂O₃ + P₂O₅.
(b) N₂O₃ + 2NH₄Cl = 2N₂ + 3H₂O + 2HCl.
[Illustration: FIGURE 16. GANTTER’S NITROGEN APPARATUS.]
It is seen from the above that the nitrate will give, by this
treatment, double the volume of nitrogen which it contains. In
practice, the two reactions may be secured in one operation by warming
the nitrate solution slowly with sulfuric and phosphorous acids and
ammonium chlorid. The nitric acid, as it becomes free, gives a part
of its oxygen to the phosphorous compound, and the nitrous acid, in
a nascent state, is at once reduced by the ammonium chlorid. There
are two sources of error which must be guarded against in the work; a
portion of the nitrogen may escape reduction to the elementary state,
or some of the nitrate may fail to be decomposed. These errors are
easily avoided if the reaction be begun slowly, so that the evolution
of gas may be gradual. The temperatures at first should, therefore,
be kept as low as possible. The development of red fumes, showing the
presence of undecomposed nitrogen oxids, shows that the results will be
too low. It is necessary, also, to provide for the absorption of the
hydrochloric acid which is formed. The reaction is very conveniently
conducted in the apparatus shown in Fig. 16. The decomposition takes
place in the flask A and the mixed gases pass into the absorption bulb
C. The delivery-tube is very much expanded, as shown in the figure,
so that no soda-lye can enter A during the cooling of the flask. The
absorption bulb is connected with A and B by the tubes a and b as
shown. The tube d connects the apparatus with the gasvolumeter.[181]
The bulb B serves as a pipette for the introduction of the decomposing
acid. The operation is conducted as follows: Three cubic centimeters
of the nitrate solution, containing no more than 300 milligrams
of substance, are placed in the flask A with half a gram each of
crystallized ammonium chlorid and phosphorous acid. In the bulb B are
placed seven cubic centimeters of sulfuric acid to which has been
added one-third its volume of water. Two cubic centimeters of acid are
allowed to flow from B into A. The apparatus is brought to a constant
temperature by being immersed in a large cylinder, E, containing water
at a temperature which can easily be controlled. When this constant
temperature has been reached the apparatus is taken from the cooling
cylinder which contains also a smaller cylinder, D, nearly filled
with water and connected through f′ with the measuring apparatus M.
The barometer-tube F is half filled with colored water so that the
pressure may be equalized before and after the operation. The flask A
is warmed very gently at first, and the nitrogen evolved is conducted
into D driving an equivalent volume of water into M. The evolution of
the gas must be carefully controlled and the heat at once removed if it
become too rapid. The appearance of a red color shows the evolution of
oxids of nitrogen rendering the analysis inexact. When the evolution of
nitrogen has nearly ceased the lamp is removed and some more sulfuric
acid allowed to flow into A from B, after which A is again heated, this
time to the boiling-point. All vapors of hydrochloric acid produced are
absorbed by the soda-lye in C. The boiling is continued a few minutes,
but not long enough to darken the liquid in A. After replacing the
apparatus in the cylinder E and bringing both temperature and pressure
to the same point as before the beginning of the operation, the volume
of nitrogen evolved is determined by measuring the water in M.
The apparatus is first set by using pure potassium or sodium nitrate.
Since the temperature and pressure do not vary much within an hour or
two the volume of water obtained with a sample of white saltpeter can
be compared directly with that given off by the same weight of a pure
potassium or sodium nitrate without correction.
_Example._—Two hundred and fifty milligrams of potassium nitrate,
containing 34.625 milligrams of nitrogen, displaced in a given case
sixty cubic centimeters of water; therefore one cubic centimeter
of water equals 0.578 milligram of nitrogen. If 289 instead of 250
milligrams be taken then the number of cubic centimeters of water
displaced divided by five will give the per cent of nitrogen.
=217. Method of Difference.=—In the analysis of Chile saltpeter by the
direct method a variation of 0.25 per cent in the content of nitrogen
is allowed from the dealers’ guaranty. This would allow a total
variation in the content of sodium nitrate of 1.52 per cent. Dealers
and shippers have always been accustomed to estimate the quantity
of sodium nitrate in a sample by difference; _i. e._, by estimating
the constituents not sodium nitrate and subtracting the sum of the
results from 100. Chile saltpeter usually contains sodium nitrate,
water, insoluble ferruginous matters, sodium chlorid, sodium sulfate,
magnesium chlorid, sodium iodate, calcium sulfate and sometimes small
quantities of potassium nitrate.
When the total sodium nitrate is to be estimated by difference the
following procedure, arranged by Crispo,[182] may be followed:
_Water._—Dry ten grams of the finely powdered sample to constant weight
at 150°-160°.
_Chlorin._—The residue, after drying, is dissolved and the volume
made up to one-fourth liter with water and the chlorin determined in
one-fifth thereof and calculated as sodium chlorid.
_Insoluble._—Twenty grams are treated with water until all soluble
matter has disappeared, filtered on a tared gooch, and the filtrate
dried to constant weight.
_Sulfuric Acid._—The sulfuric acid is precipitated by barium chlorid
in the slightly acid filtrate from the insoluble matter. The acidity
is produced by a few drops of nitric acid. The rest of the process is
conducted in the usual way.
_Magnesia._—This is precipitated by ammonium sodium phosphate,
filtered, ignited, and weighed as pyrophosphate. The magnesium is then
calculated as chlorid. Magnesia is rarely found in excess of one-fourth
per cent. When this amount is not exceeded the estimation of it may be
neglected without any great error. As has already been said the chlorin
is all calculated as sodium chlorid. If a part of it be combined with
one-fourth per cent of magnesia it would represent 0.59 per cent of
magnesium chlorid instead of 0.73 per cent sodium chlorid. In omitting
the estimation of the magnesia therefore the importer is only damaged
to the extent of 0.14 per cent of sodium nitrate.
_Sodium Iodate._—This body, present only in small quantities, may also
be neglected. In case the content of this body should reach one-fourth
per cent the estimation of chlorin by titration using potassium
chromate as indicator is impracticable. Such an instance, however, is
rarely known.
_Approximate Results._—When the determinations outlined above have been
carefully made it is claimed that the result obtained by subtraction
from 100 will not vary more than from two-tenths to three-tenths per
cent from the true content of sodium nitrate. The method, however,
cannot be considered strictly scientific and is much more tedious
and chronophagous than the direct determination. In the direct
determination, however, the analyst must assure himself that potassium
is present in only appreciable quantities otherwise the per cent of
sodium nitrate will be too low.
The presence of potassium nitrate is a detriment in this respect
only; _viz._, that it contains a less percentage of nitrogen than
the corresponding sodium salt. As a fertilizer, the value of Chile
saltpeter may be increased by its content of potassium.
=218. The Application of Chile Saltpeter to the Soil.=—The analyst
is often asked to determine the desirability of the use of sodium
nitrate as a fertilizer and the methods and times of applying it.
These are questions which are scarcely germane to the purpose of this
work but which, nevertheless, for the sake of convenience may be
briefly discussed. In the first place it may be said that the data of
a chance chemical analysis will not afford a sufficiently broad basis
for an answer. A given soil may be very rich in nitrogen as revealed
by chemical analysis, and yet poor in an available supply. This is
frequently the case with vegetable soils, containing, as they do, large
quantities of nitrogen but holding it in practically an inert state.
I have found such soils very rich in nitrogen, yet almost entirely
devoid of nitrifying organisms. It is necessary therefore in reaching a
judgment on this subject from analytical data to consider the different
states in which the nitrogen may exist in a soil and above all the
nitrifying power of the soil if the nitrogen be chiefly present in
an organic state. Culture solutions should therefore be seeded with
samples of the soil under examination and the beginning and rapidity
of the nitrification carefully noted. In conjunction with this the
nitrogen present in the soil in a nitric or ammoniacal form should be
accurately determined. These determinations should be made according to
the directions given in the first volume, pp. 448-548.
For the determination of nitrifying power we prefer the following
method:
=219. Taking Samples of Soil in Sterilized Tubes.=—Brass tubes are
prepared twenty centimeters in length and one and a half in diameter.
One end is ground to a beveled edge and compressed in a mold so as to
make the cutting edge slightly smaller in diameter than the internal
diameter of the tube. It is then ground or filed until smooth and
sharp. The blunt end of the tube is stoppered loosely with cotton and
it is then sterilized by heating for an hour to 150°. Rubber caps
are provided and each one has placed at the bottom a rubber ball to
prevent the rubber from being cut by the edges of the brass tube. The
caps should be of two distinct colors. Half of the rubber caps are
sterilized by being boiled for an hour in water for three successive
days. The caps cannot be heated to 150° dry heat with safety. On
removing the brass tube from the sterilizing oven as soon as it is cool
enough to handle, a sterilized rubber cap is slipped over its cutting
end. An unsterilized cap is then slipped over the other end containing
the cotton plug. Inasmuch as the cotton plug is never removed it is not
necessary to sterilize the cap covering it. Large numbers of the tubes
can thus be prepared for use and they can be safely transmitted to a
distance by express or mail. For convenience, each tube is encased in a
small cloth bag, which is tied with a cord carrying a tag on which the
necessary data can be recorded at the time of taking the sample.
The tubes and their rubber caps thus carefully sterilized should not
be removed from their cloth envelopes until the moment of taking each
sample. After the sample has been taken and the cap replaced on the
tube the latter should be immediately enclosed in the cloth sack and
labeled with one of the tags therewith enclosed. The sample should
be taken in two kinds of soil, in one instance in a cultivated soil,
which is most characteristic of the locality, and in the second place
a virgin soil of the same type. The virgin soil may be either soil
which has been covered with grass or in forest. The spots at which the
samples are to be taken having been previously selected, the tags for
each tube should be prepared beforehand so as to avoid delay at the
time of sampling. A pit with straight walls should be dug, the sides of
which are at least two feet wide and even three feet would be better.
The pit should be about forty-two inches deep. One of the sides having
been made perfectly smooth and without allowing the loose fragments
from the top to fall down and adhere to the walls below, the spots at
which the samples are to be taken should be marked with a tape line
at the following points; _viz._, three, fifteen, twenty-seven, and
thirty-nine inches, respectively, below the surface. Beginning at the
bottom point, carefully scrape off the surface of the wall over an
area slightly larger than that of the end of the sample tube by means
of a spatula, which, just previous to use, has been held for a moment
or two in the flame of an alcohol or other convenient lamp. The sample
tube having been removed from its sack, it will be noted that the end
covered with black rubber is the one which is to be held in the hand,
and this black rubber cap should be first removed being careful not
to extract the plug of sterilized cotton which closes the end of the
tube. Holding the tube firmly by the end, the fingers extending only
about two inches from the end, remove the light-colored cap and push
the tube with a turning motion into the side of the pit at the point
where the surface has been removed with the sterilized spatula. When
this is properly done the tube will be filled with a cylinder of soil
equal to the length of the part of the tube penetrating the wall of the
pit. The tube is then withdrawn, the light rubber cap first replaced,
and then the black one. The light rubber cap should be held in the hand
during the process in such a way that no dust or particles of soil are
permitted to contaminate its inner walls. For this purpose the open
end of the cap should be held downward. For the same reason after the
removal of the light rubber cap the brass tube should be carefully
preserved from dust or fragments, the open end, that is the cutting
end, being held downward until ready for use. After one tube has been
filled, capped, replaced in the sack and labeled, the spatula should be
again sterilized and samples taken in regular order until the top one
is finished.
=220. Directions for Taking Bulk Samples.=—From the sides of the pit
described above, bulk samples should be taken as follows:
By means of a spade the soil should be removed from the four sides to
the depth of six or nine inches or until the change of color between
the soil and subsoil is noted; in all enough to make about 150 pounds
of the air-dried soil. In the same way take a sample of the subsoil to
the depth of nine additional inches. Remove all stones, large pebbles,
sticks, roots, etc., and spread the samples in a sheltered place where
they can be air-dried as rapidly as possible. The bulk samples should
be taken both from the cultivated and virgin soils. In selecting the
cultivated soil, preference should be given to those soils which have
not been fertilized within a few years. If recent fertilization have
been practiced the character and amount of it should be noted.
=221. The Nitrifiable Solution.=—The solution to test the nitrifying
power of the samples collected as above described is conveniently made
as follows:
Potassium phosphate, one gram per liter.
Magnesium sulfate, half a gram per liter.
Calcium chlorid, a trace.
Ammonium sulfate, 200 milligrams of nitrogen per liter.
Calcium carbonate, in excess.
One liter of the above solution is enough for ten samples, each of 100
cubic centimeters. This quantity is placed in an erlenmeyer, which
is stoppered with cotton and sterilized by being kept at 100° for an
hour on three successive days. The erlenmeyer should be sterilized
beforehand by heating for an hour at 150°. The freshly precipitated and
washed calcium carbonate should be sterilized separately and added to
each erlenmeyer at the time of seeding. Enough should always be used
to be in excess of the nitrous and nitric acids found. The seeding is
accomplished by filling a sterilized spoon which holds approximately
half a gram of the soil, from the contents of one of the brass tubes,
lifting the plug in the erlenmeyer and transferring quickly to the
flask. This should be done in a perfectly still room, preferably
as high above the ground as possible and in a place free from dust
and under cover. The cotton plug being replaced the erlenmeyer is
shaken until the sample of soil added is thoroughly disintegrated
and intimately mixed with its contents. With care and experience
the seeding is easily accomplished without danger of accidental
contamination.
At the end of each period of five days the beginning and progress of
nitrification should be determined by some of the methods described in
volume first. Either the ammonia can be determined by nesslerizing or
the nitrous and nitric acids estimated. For nitrous acid we prefer the
method described in volume first, paragraph =504=, and for nitric the
one in same volume paragraphs =497= and =498=.
By supplementing the analysis of a soil by the above described
experiments in nitrification the analyst will be able to judge with
sufficient accuracy of its needs for nitric nitrogen.
=222. Quantity of Chile Saltpeter to be Applied.=—The quantities of
Chile saltpeter which should be applied per acre vary with so many
conditions as to make any definite statement impossible. On account
of the great solubility of this salt no more should be used than is
necessary for the nutrition of the crop. For each 100 pounds used,
from fourteen to fifteen pounds of nitrogen will be added to the soil.
Field crops, as a rule, will require less of the salt than garden
crops. There is an economic limit to the application which should not
be passed. As a rule 250 pounds per acre will prove to be a maximum
dressing. The character of the crop must also be considered. Different
amounts are required for sugar beets, tobacco, wheat, and other
standard crops. It is rarely the case that a crop demands a dressing of
Chile saltpeter alone. It will give the best effects, as a rule, when
applied with phosphoric acid or potash. But this is a branch of the
subject which cannot be entered into at greater length in this manual.
The reader is referred to Stutzer’s work on Chile saltpeter for further
information.[183]
=223. Consumption of Chile Saltpeter.=—The entire consumption of sodium
nitrate for manurial purposes in the whole world for 1894 was 992,150
metric tons, valued at $41,000,000. For the several countries using it
the consumption was distributed as follows:
Germany 397,200 tons.
France 187,100 “
England 117,000 “
Belgium 123,000 “
United States 100,000 “
Holland 56,700 “
Italy and Spain 5,200 “
Other countries 5,950 “
-------
Total 992,150 “
The above figures represent the actual commerce of each country in
Chile saltpeter, and may not give the exact consumption.[184] For
instance, Germany exports sodium nitrate to Russia and Austria, but
it imports this salt from Holland and Belgium. Belgium imports from
France, but its exportation is greater than its importations from that
country, so that its actual consumption on the farm probably falls
considerably below that given on the table. Holland also exports larger
quantities than are imported from neighboring states. The exports from
England are inconsiderable compared with the quantities received,
amounting only to about 5,000 tons a year, while the exportations from
France reach nearly 10,000 tons.
Sodium nitrate has a moderate value at the factories where it is
prepared for shipment in Chile. Its chief value at the ports where
it is delivered for consumption comes from freights and profits of
the syndicate. The factories, where it is prepared for the market,
are at or near the deposits, and the freights thence to the sea coast
are very high. The rail roads which have been constructed to the high
plateaux which contain the deposits, have been built at a very great
cost, and the freights charged are correspondingly high. There is also
a tax of $1.20 levied on each ton exported. Deducting all costs of
transportation and export duties the actual value of sodium nitrate at
the factory, ready for shipment, is about sixteen dollars in gold a ton.