A course of practical work in the chemistry of the garden, for teachers and students of horticulture gardening and rural science

&SE

IN THE CI-JEMI

OF THE GARDEN

IVR JI DmRDES ~KEP

A COURSE OF PRACTICAL WORK IN
THE CHEMISTRY OF THE GARDEN

PRACTICAL
AGRICULTURAL CHEMISTRY

BY S. J. M. AULD

D.Sc.(Lond.), Ph.D. (Wiirzburg), P.I.C., P.C.S.
Professor of Agricultural Chemistry at Univertity College, Reading

And D. R. EDWARDES-KER

B.A.(Oxon.), B.Sc.(Lond.)

Head of the Chemical Dtpartment, Southeastern Agricultural College
(Univertity of London), Wye, Kent

Large Crown 8vo. xxiv+244 Pages. 32 Illustrations. SB. net.

This book is intended as a practical handbook in Agricultural
Chemistry for students working through courses of instruction for
the London B.Sc. degree in Agriculture and other examinations
of a similar type and standard.

BY A. D. HALL, M.A., F.R.S.

THE SOIL

AN INTRODUCTION TO THE SCIENTIFIC STUDY OF THE
GROWTH OF CROPS

Second Edition, Revised and Enlarged. 16 Illustrations. 55. net,

FERTILISERS AND MANURES

9 Illustrations. 55. net.

THE FEEDING OF CROPS AND
STOCK

AN INTRODUCTION TO THE SCIENCE OF
THE NUTRITION OF PLANTS AND ANIMALS

24 Illustrations. 55. net.

A COURSE OF PRACTICAL

WORK IN THE CHEMISTRY

OF THE GARDEN

FOR TEACHERS AND STUDENTS OF HORTICULTURE
GARDENING AND RURAL SCIENCE

BY D;R?JEDWARDES-KER

B.A. (OXON.), B.SC. (LOND.)

HEAD OP THE CHEMICAL DEPARTMENT AND LECTURER IN AGRICULTURAL

CHEMISTRY AT THE SOUTH-EASTERN AGRICULTURAL COLLEGE (UNIVERSITY
OF LONDON), WYE, KENT.

JOINT AUTHOR OF "PRACTICAL AGRICULTURAL CHEMISTRY."

LONDON
JOHN MURRAY, ALBEMARLE STREET, W,

1914

All rights reserved.

CONTENTS

CHAPTER I
THE CHEMISTRY OF PLANTS

PAGE

Preparation of Plant Ash . . . . < 7

Chemical Examination of Plant Ash . • .

Detection of Chemical Elements in Plants . • 9
Detection of Sugar ...... 10

Detection of Starch . . . . .11

Preparation and Properties of Cellulose . . .11

Tests for Proteins . . . . . 1 3

Preparation of Essential Oils . . . .14

CHAPTER II
THE CHEMISTRY OF SOILS

Detection of Phosphates in Soil . . . 15

Detection of Potash in Soil . . 15

Proof of Organic Nitrogen in Soil . . . 16

Preparation of Humus . . . . .16

Detection of Nitrates in Soil . .18

Nitrification by Soil Bacteria . . . .19
Detection of Calcium Carbonate in Soil ... 20

Comparison of Water-holding Capacity of Soils . . 20

Flocculation of Clay . . . • .21

6 CONTENTS

CHAPTER III
THE CHEMISTRY OF MANURES AND FERTILISERS

PAGE

Examination of Farmyard Manure . . .23

Examination of Guano . . . . .24

Examination of Shoddy . . . . .24

Examination of Nitrate of Soda . . . .25

Examination of Sulphate of Ammonia . . .26

Examination of Superphosphate . . . .27

Examination of Basic Slag . . . .27

Examination of Kainit . . » .28

Examination of Sulphate of Potash . . .29

Incompatible Mixture of Superphosphate and Nitrate

of Soda ...... 29

Incompatible Mixture of Basic Slag and Sulphate of

Ammonia ...... 30

Examination of Lime ..... 30

CHAPTER IV
THE CHEMISTRY OF SPRAYS AND WASHES

Preparation of Lead Arsenate Wash . . -33

Determination of Lathering Power of Soap . . 34

Preparation of Paraffin Soft- Soap Emulsion . . 35

Preparation of Paraffin Jelly . . . .36

Preparation of Bordeaux Mixture . . . • 37

Preparation of Lime-Sulphur . . . .38

APPENDIX .... • • 39

CHEMISTRY OF THE GARDEN

CHAPTER I

THE CHEMISTRY OF PLANTS

THE ash obtained by ignition of leaves and other parts of
plants represents the mineral constituents that have been
obtained from the soil during the life of the plant. The
ash contains calcium (lime), potassium, iron, carbonates,
sulphates, phosphates, etc., and in those cases in which it is
obtained in quantity (e.g. bonfire ashes), is of value as a
fertiliser.

EXPERIMENT I. Preparation of Plant Ash.

Some leaves or other portions of plants are placed
in a porcelain basin, and heated over a Bunsen
burner. Steam is at first produced from water in
the material, and then charring occurs owing to
the burning of the dry matter. The heating is
continued until all blackness due to the presence
of unburnt carbonaceous matter disappears, and the
greyish or white residue of plant ash is allowed
to cool and used for the next experiment.

8 THE CHEMISTRY OF PLANTS [CHAP.

EXPERIMENT 2. Chemical Examination of
Plant Ash.

(a) Some of the ash is dissolved in a very small
quantity of concentrated hydrochloric acid. The
effervescence noticeable is due to the presence of
carbonates in the ash.

(b) Some of the solution so obtained is diluted
with its own volume of water,, and then treated
in two portions with potassium ferrocyanide and
potassium thiocyanate respectively. In the first
case a blue precipitate, in the second a red colora-
tion, show the presence of iron.

(c) To some of the solution of the ash in hydro-
chloric acid is added a few drops of barium chloride
solution. The presence of sulphates is indicated by the
production of a white precipitate of barium sulphate.

(d) Some of the original ash is dissolved in a
little concentrated nitric acid, some ammonium
molybdate solution added, and the whole boiled.
A canary-yellow precipitate shows the presence of
phosphates.

(e) To a solution of the ash in dilute nitric acid
is added some silver nitrate solution. The presence
of chlorides is indicated by the white precipitate of
silver chloride.

The presence of the above constituents, and, in addition,
nitrogen, which is lost during the process of ignition, may
be shown directly in plants without incineration.

i.] CHEMICAL ELEMENTS IN PLANTS 9

EXPERIMENT 3. Detection of Chemical
Elements in Plants.

(a) Carbon. Some leaves are cut into pieces,
placed in a test-tube, and granulated copper oxide
added. A cork provided with a delivery-tube is
placed in the end of the tube, and the contents are
then heated over a Bunsen burner. Carbon dioxide
will be produced, as shown by passing the gases
evolved into lime water contained in another test-
tube, when the lime water will become milky.

C + 2CuO = CO2+2Cu

(b) Nitrogen. Some pea- meal, or other plant
material finely chopped, is mixed with twice its bulk
of soda-lime and heated in a test-tube. Under
these conditions the nitrogen-containing bodies give
ammonia, the presence of which can be demonstrated
by holding a piece of red litmus paper in the gases
evolved at the mouth of the test-tube.

(c) Phosphorus. A few crystals of potassium
nitrate (saltpetre) are heated in a test-tube until
they melt, and many successive small portions of
pea-meal added on the point of a knife. After each
addition of material the nitrate should be heated
until all action is at an end. The mass is then
allowed to become quite cold, after which it is
dissolved in warm water and the solution obtained
divided into two portions. To one is added nitric

B

10 THE CHEMISTRY OF PLANTS [CUAP.

acid and ammonium molybdate, and the mixture
warmed. A yellow precipitate indicates phosphate
that has been formed from phosphorus-containing
bodies in the pea-meal.

(d) Sulphur. The second portion of the solution
obtained is treated with hydrochloric acid and barium
chloride, the formation of a white precipitate showing
the presence of sulphate produced from sulphur-
containing bodies in the peas.

The presence may be shown in plants of many substances
which are destroyed during the process of ashing or ignition
with potassium nitrate. Starch, sugar, cellulose (fibre), gum
and other similar carbohydrates containing no nitrogen and
built up by the plant from the carbon dioxide of the air, and
proteins or nitrogenous bodies formed from carbon dioxide in
conjunction with nitrates obtained from the soil, are examples
of such compounds. The value of plants as human and
animal foods depends largely upon the presence of these
bodies.

EXPERIMENT 4. Detection ofSttgar.

Some carrots, raisins, or ripe fruits (plums, apples)
are cut up and boiled with water in a flask for some
little time. The sugars are thereby extracted
together with other water-soluble constituents, and
their presence may be shown by boiling some of the
aqueous extract with Fehling's solution,1 when a
brick-red precipitate of cuprous oxide, Cu2O, will
be obtained.

1 See Appendix.

I.] STARCH AND CELLULOSE 11

Starch exists in plants in the form of granules, which vary
in size and shape according to the plant in which they are
produced.

EXPERIMENT 5. Detection of Starch.

A small potato, after washing and peeling, is grated
to a pulp, and the latter tied up in a piece of linen.
The bag and contents are then well kneaded under
water in a beaker, whereby the fine starch granules
pass through the interstices of the cloth. The
turbid liquid is allowed to settle, and the water
poured off from the starch. A very small quantity
of the latter is transferred by a glass rod to a test-
tube half full of water, which is then boiled for a few
minutes. After cooling, a single drop of a solution
of iodine in potassium iodide1 is added, the deep
blue colour produced being indicative of starch.
This blue colour is discharged on heating to 80° C,
but returns on cooling.

Cellulose is found in largest quantity in the woody or fibrous
parts of plants, and gives rigidity to the structure. The older
the plant, the more fibrous and tougher is the texture of the
cellulose.

EXPERIMENT 6. Preparation and Properties of
Cellulose.

Some stalks of plants, or full-grown leaves, are finely
chopped, and boiled with dilute sulphuric acid for
half an hour. The undissolved matter is collected
1 See Appendix.

12 THE CHEMISTRY OF PLANTS [CHAP.

on a piece of cloth, washed with hot water, and
then boiled for another half-hour with dilute caustic
soda solution. After washing with water, the cellu-
lose so obtained is subjected to the following tests : —

(a) A small portion is vigorously shaken in a
corked test-tube with Schweizer's reagent1 The
cellulose will become disintegrated and gradually
dissolved. The common solvents, water, ether,
alcohol, dilute acids and alkalis, are without action
on cellulose.

(b) About I c.c. of concentrated sulphuric acid is
placed in a test-tube and small pellets of the
cellulose dropped in at intervals, as the previous
portions dissolve with shaking. When the rate of
dissolution of the cellulose becomes slow, the test-
tube is nearly filled with water, and the solution
so obtained boiled in a beaker for five minutes. A
portion is then rendered alkaline with very strong
(syrupy)1 caustic soda solution, Fehling's solution
added, and the mixture boiled. The red precipitate
shows the presence of sugar that has been formed
from the cellulose, the chemical structure of these
two bodies being very similar. By suitable fermen-
tation of this sugar, alcohol could be obtained, and
this is the basis of the process of manufacture of
alcohol from sawdust, wood pulp, etc.

C0H1006 + H20 = CCH1206

(Cellulose) (Grape Sugar)

1 See Appendix.

L] TESTS FOR PROTEINS 13

The complex nitrogenous compounds called proteins make
up the " flesh " of plants, and are especially abundant in peas,
beans, and other plants of' the leguminous order. These
plants do not, however, require excessive nitrogenous manuring
on this account, as they alone of all plants possess the
power of obtaining the nitrogen they require from the air
(nitrogen fixation}.

EXPERIMENT 7. Tests for Proteins.

Pea-meal, which contains about one quarter of its
weight of a protein called legumin^ is examined
as follows : —

(a) Xantho-proteic reaction. A small quantity of
the meal is heated with i c.c. of concentrated nitric
acid in a test-tube until completely dissolved. To
the light yellow solution is cautiously added syrupy
caustic soda solution1 until alkaline. Immediately
the acidity is neutralised the colour will suddenly
deepen to dark yellow or orange.

(b) Biuret reaction. A trace of pea-meal is dis-
solved in caustic soda solution with the application
of heat, and to the resulting liquid after cooling is
added I or 2 drops of a very dilute solution
of copper sulphate. A violet colour will be
produced.

(c) Adamkiewicz 's reaction. A little pea-meal is
dissolved in glacial acetic acid with gentle heating.
The test-tube containing this solution is inclined

1 See Appendix.

14 THE CHEMISTRY OF PLANTS [CHAP. i.

at an angle of 45°, and about i c.c. of concentrated
sulphuric acid poured slowly down the inside so as
to form a layer at the bottom of the acetic solution.
A violet ring appears at the junction of the two
liquids, the colour deepening on standing.

Many garden plants, lavender, rosemary, sage, mint, etc.,
contain essential oils, to which their odour and their value
is due.

EXPERIMENT 8. Preparation of Essential Oils.

Some lavender heads, or finely chopped leaves of
the plants mentioned, are placed in a retort together
with sufficient water. A round-bottomed flask large
enough to allow the neck of the retort to reach well
into it, is clamped almost horizontally, and a steady
stream of water arranged to run over it. On
boiling the contents of the retort, steam together
with essential oil passes into the flask, and both are
there condensed. The essential oil may be readily
extracted by shaking the distillate with about one
quarter of its bulk of petroleum ether, separating
the ethereal layer, and distilling off the ether on a
water-bath by means of suitable apparatus.

(Caution. — Petroleum ether should not be brought
within six feet of a flame?)

CHAPTER II

CHEMISTRY OF SOILS

THE soil is the source of all the mineral constituents, and also
the nitrogen, of plants. Fertile soils can hence be shown to
contain phosphates, sulphates, lime, potash, magnesia, organic
nitrogen, nitrates, etc.

EXPERIMENT 9. Detection of Phosphates in Soil.

A small quantity of a fertile soil is ignited in a
porcelain basin in order to burn off organic matter.
The material is then boiled in a test-tube with a few
cubic centimetres of concentrated nitric acid, and
after cooling and settling, the clear liquid decanted
off. Ammonia solution insufficient in amount to
neutralise all the acid is added, followed by
ammonium molybdate solution. On warming, the
characteristic yellow precipitate indicating phosphates
is observed.

EXPERIMENT 10. Detection of Potash in Soil.

By boiling some soil with dilute hydrochloric acid
in a test-tube, potash salts together with certain

15

16 CHEMISTRY OF SOILS [CHAP.

other compounds are extracted. The solution is
filtered, the filtrate evaporated to dryness in a basin,
and the residue heated to redness over a Bunsen
burner. Silica and other bodies are rendered in-
soluble by this treatment. The cooled mass is then
scraped into a test-tube, shaken with a little cold
water, and the solution of potassium chloride so
obtained filtered from insoluble matter. The pres-
ence of potash is shown in the clear liquid by the
addition of a little acetic acid, followed by some
sodium cobaltinitrite x solution, when a reddish pre-
cipitate will be obtained.

All plants excepting those of the pea and bean family
(leguminosa) are entirely dependent on the soil for their
nitrogen. The reserve form in which this nitrogen exists in the
soil is humus, a complex nitrogenous organic compound pro-
duced by the bacterial decay of vegetable and animal matter.

EXPERIMENT 1 1. Proof of Organic Nitrogen
in Soil.

A small quantity of soil is tested as in experiment
3 (#) above.

EXPERIMENT 12. Preparation of Humus.

Thirty or forty grams of a peaty soil are placed in
a beaker of suitable size, and about half full of dilute
hydrochloric acid. The mixture is well stirred as

1 See Appendix.

ii.] HUMUS 17

long as it effervesces, after which it is poured into a
piece of calico about a foot square. The corners of
the cloth are gathered together, and as much liquid
as possible squeezed out. The residue is returned to
the beaker, well stirred with water, and the mixture
again poured into the calico and squeezed dry. This
process is repeated until the water squeezed out does
not give an acid reaction (red coloration) [with litmus
paper. The solid matter which is now free from
acid is once again placed in the beaker, and dilute
ammonia solution added to the half-way mark. The
whole is thoroughly mixed and allowed to stand for
some hours, or even days, whereby the humus is
dissolved out in the ammonia. The coffee-coloured
liquid is then separated from the solid matter, using
a piece of cloth as before, but this time the liquid
portion is saved. To this liquid is carefully added
strong hydrochloric acid until a bulky precipitate of
humus (humic acid) is formed. This precipitate is
filtered off by means of a funnel and filter paper, and
a portion tested for organic nitrogen as in experi-
ments 3 (b) and n.

Although humus is the reserve form of nitrogen in the soil,
this nitrogen is not assimilable by plants until it has been
converted into nitrate by bacterial agencies. The necessary
nitrifying bacteria are present in all soils, consequently all
soils contain appreciable amounts of nitrates. The nitrates
never accumulate in ordinary soils, as they are too rapidly
removed by growing plants, and by the washing or leaching
action of rain water.

C

18 CHEMISTRY OF SOILS [CHAP.

EXPERIMENT 13. Detection of Nitrates in Soil.

About twenty grams of soil are shaken with 100
c.c. of distilled water, the soil allowed to settle and
the clear liquid filtered off. About 2 c.c. of this
filtered extract are poured into a test-tube, and a
sufficient amount (3 to 5 drops) of a solution of
diphenylamine x in pure sulphuric acid added to give
a distinct milkiness. This milky liquid is then care-
fully poured on to the surface of i c.c. of pure nitrate-
free sulphuric acid contained in another test-tube,
and the junction of the two liquids examined. A
blue ring should be immediately produced, or, if the
amount of nitrate present is small, will gradually
develop. If there is no visible blue ring after five
minutes, some of the filtered soil extract should be
concentrated to a small bulk by boiling, and then
again tested.

The experiment is of course valueless if there is
the slightest trace of nitrates in either the sulphuric
acid or distilled water used, and these reagents should
be carefully tested prior to making the examination.

Nitrification is the term applied to the conversion in the
soil of ammonium salts into nitrates by the agency of specific
bacteria in conjunction with the oxygen of the air. Organic
nitrogen (in humus, farmyard manure, shoddy, etc.) is first
changed into ammonium salts by other bacterial action,
nitrification of these ammonium compounds then taking

1 See Appendix.

IL] NITRIFICATION 19

place. As a plentiful supply of air is required for this latter
change, it is stimulated by tillage, owing to the resultant
aeration of the soil.

EXPERIMENT 14. Nitrification by Soil Bacteria.

A solution for the nutrition of the bacteria is
made up as follows : — 3 grams potassium phosphate,
2 grams ammonium sulphate, i gram magnesium
sulphate, a trace of common salt, and 2 drops of
dilute ferric chloride solution, are added to I litre
of water and well shaken. One hundred c.c. of this
solution are placed in each of two flasks, the mouths
of which are .then plugged with cotton wool The
flasks and their contents are sterilised by boiling for
five minutes, and after cooling the plugs are removed,
and about J gram of chalk, previously sterilised by
heating, introduced into each. To one flask only is
also added a pinch of arable soil. The two flasks
are again plugged and placed in a warm cupboard.
Every three or four days some of the solution is
removed from each flask and tested separately for
nitrates with diphenylamine and sulphuric acid. If
the experiment has been carefully carried out, the
liquid in the flask to which no soil was added should
show no nitrate reaction for some weeks, while the
contents of the other flask should give a pronounced
blue ring at the first time of testing.

The presence in soil of a certain percentage of calcium
carbonate (chalk), or " lime " as it is wrongly called, is of the

20 CHEMISTRY OF SOILS [CHAP.

utmost importance for many reasons (see page 30), and the
cropping power of many soils may be considerably increased
by the application of chalk, or lime which rapidly undergoes
conversion into chalk.

EXPERIMENT 15. Detection of Calcium Carbonate
in Soil.

About a gram of dry soil is placed in a test-tube,
and covered with a few cubic centimetres of dilute
hydrochloric acid. The mixture is shaken, and the
amount of effervescence produced by the action of
the acid on the chalk is observed. If there is a
visible effervescence, it may be concluded that the
soil contains a sufficiency of chalk. If the mouth of
the test-tube has to be brought to the ear before the
effervescence can be heard, an application of chalk
or lime would probably be beneficial, while if no
effervescence can be detected at all, the soil examined
is badly in want of treatment in this direction.
CaCO3+2HCl = CaCl2+H20 + C02

(Chalk)

The water-holding capacity of soils, and consequently their
ability to withstand drought, depends mainly upon the fineness
of division of the soil particles ; the smaller the particles, the
greater the retentive power for water.

EXPERIMENT 16. Comparison of Water-holding
Capacity of Soils.

Four ordinary lamp glasses are fitted at the
bottom with pieces of calico tightly stretched and

IT.] FLOCCULATION OF CLAY 21

firmly tied. The four vessels so improvised are
filled to exactly the same height with air-dry
samples of (a) coarse sand, (&) a loam, (c) a heavy
clay soil, (d) a peaty soil or peat moss, in the
respective cases, and they are then clamped in
vertical positions over medium-sized beakers. Two
hundred c.c. of water are then poured on the top of
the soil in each of the glasses, and the drainings
collected in the beakers below. By measuring the
volumes of liquid collected when drainage is com-
plete, a comparison of the water-retaining capacities
is made.

Successful treatment of heavy clay land is one of the most
difficult problems of work in the garden or field. Clay if
treated or worked when in a wet condition, readily becomes
sticky and " puddled," or " deflocculated " as it i s scientifically
termed. Such puddled clay is unworkable, and even after
drying is extremely intractable and difficult to deal with.
This undesirable condition can be corrected by several
different agencies that bring about flocculation, such as the
action of frost, or by treatment with lime, chalk, or certain
salts.

. EXPERIMENT 17. Flocculation of Clay.

A small quantity of clay is deflocculated by knead-
ing with distilled water in a beaker, more water then
being added to the sticky mass to bring it to the
consistency of a thin cream after well mixing. This
cream is diluted to about i litre with water, and
after allowing any stones or other large particles to

22 CHEMISTRY OF SOILS [CHAP. n.

settle, the turbid liquid is poured in lots of 200 c.c.
into four gas cylinders.

To No. i is added I c.c. dilute hydrochloric acid.

To No. 2 is added 5 c.c. lime water.

To No. 3 is added i c.c. dilute caustic soda solution.

While 4 is kept as a control.

The contents of each cylinder are well stirred, and
are then allowed to settle. The rapidity of clearing
of the columns of liquid is noted, when it will be
found that the acid is strongly deflocculating in its
effect, the lime water also fairly strongly so, while
the caustic soda has the effect of keeping the clay
particles permanently deflocculated.

CHAPTER 111

CHEMISTRY OF MANURES AND FERTILISERS

CONTINUED cropping results in an impoverishment of the
soil by a gradual removal of the mineral constituents and
nitrogen. The constituents on which these losses fall most
heavily are nitrogen, phosphates, and potash salts, and the
supply of these is kept up by the addition of fertilisers con-
taining them. Such artificially added plant foods may be
either of organic (animal or vegetable) origin, e.g. farmyard
manure, shoddy, guanos, bone meal, in which case they add
also valuable humus to the soil ; or of inorganic origin, e.g.
nitrate of soda, superphosphate, potash salts.

MANURES OF ORGANIC ORIGIN.

Farmyard manure contains nitrogen, phosphates, and
potash, but varies considerably in composition. The large
amount of organic matter present is converted on decomposi-
tion into humus, a substance of great value on account of the
improvement it effects in the texture and water-holding
capacity of soil.

EXPERIMENT 18. Examination of Farmyard
Manure.

The presence of nitrogen in farmyard manure is
shown by the method used in Experiment 3 (#).

28

24 MANURES AND FERTILISERS [CHAP.

Some of the manure is dried, and then strongly
ignited, the ash so obtained being tested for phos-
phates and potash as in Experiments 2 (d) and 10
respectively.

Guanos are valuable fertilisers possessed of an extremely
high reputation, and commanding a high price in consequence.
Consisting of the consolidated dung of sea-birds, they contain
when fresh both nitrogen (up to 14 per cent.) and phosphates
(up to 9 per cent.). If originally deposited on islands subject
to occasional rains, the more soluble nitrogenous constituents
have been washed out, and the material is then phosphatic
only. Fish "guano" and meat "guano" are not guanos in
the true sense of the term, but are nevertheless valuable
manures.

EXPERIMENT 19. Examination of Guano.

The colour of the material should be noted, as
guanos containing both nitrogen and phosphates are
grey, while the phosphatic guanos are reddish or
brown. Chemical tests for nitrogen and phosphates
should be applied.

Other manures of organic origin are shoddy (nitrogenous
only, and especially valued for hops and fruit trees), bone
meal (nitrogenous and phosphatic), dried blood (nitrogenous),
steamed bone flour (phosphatic only), and rape dust (mainly
nitrogenous, traces of phosphates and potash).

EXPERIMENT 20. Examination of Shoddy.

The points on which shoddy is valued are: (i)
content of nitrogen ; (2) texture. A sample of

ill.] NITRATE OF SODA 25

shoddy should be examined to determine whether
the material is lumpy or homogeneous, and coarse
or finely divided The best shoddies (above 9
per cent, nitrogen) are like wool in appearance, while
low-grade samples (below 4 per cent, nitrogen) are
generally dirty, lumpy, with little of the texture
of the original wool.

FERTILISERS NOT OF ORGANIC ORIGIN.

Nitrogenous. Nitrate of Soda, Sulphate of Ammonia, and
the new fertilisers prepared from atmospheric nitrogen, nitrolim
or calcium cyanamide, and nitrate of lime.

Phosphatic. Superphosphate. Basic Slag.

Potassic. Kainit. Sulphate of Potash. Potash Salts.

Nitrate of soda is a natural deposit found a few feet below
the surface in Chile, Bolivia, and Peru. It is subjected to a
crude method of purification on the spot by crystallisation
from water. It contains 16 per cent, of nitrogen.

EXPERIMENT 21. Examination of Nitrate
of Soda, NaNO3.

(i.) A few crystals are exposed to the air for an
hour or so. They rapidly become moist, and finally
dissolve in the water they absorb from the atmo-
sphere. Nitrate of soda should therefore not be
stored in sacks in moist localities. (The same
applies to nitrate of lime.)

(ii.) A few crystals are shaken up with water in
a test-tube and will be found rapidly to dissolve.
Nitrate of soda is hence speedily dissolved in the
soil water, and coming into quick contact with the

D

26 MANURES AND FERTILISERS [CHAP.

plant roots, acts as an extremely rapid fertiliser. For
the same reason it is washed away into the drains,
if there be not already growing plants in possession
of the ground ready to utilise it.

Sulphate of ammonia is a by-product in the manufacture of
ordinary coal gas. Most samples are greenish in colour,
and contain about 20 per cent, of nitrogen.

EXPERIMENT 22. Examination of Sulphate of
Ammonia, (NH4)2 SO4'.

(i.) A little 'of the fertiliser is heatdfcl in a basin
or on a piece of sheet iron over a Bunsen burner.
The substance is entirely converted into vapour,
and no residue should be left.

(ii.) A few crystals are exposed to the air as in
Experiment 21 (i.). There will be no absorption of
atmospheric moisture.

(iii.) Some of the substance is dissolved in water,
and will be found to do so readily. It is not so
quick-acting a fertiliser as nitrate of soda, however,
as it has first to undergo nitrification before it can
be utilised by plants. In spite of its ready solubility
it is not washed out of even fallow land, as it is held
firmly by certain soil constituents.

(iv.) Some of the solution obtained is boiled with
caustic soda and the smell of ammonia so produced
is noticed, and tested with red litmus paper.

Superphosphate is prepared by treating certain ground

IIL] SUPERPHOSPHATE 27

mineral phosphates with sulphuric acid, whereby a large pro-
portion of the insoluble phosphate is rendered soluble.

EXPERIMENT 23. Examination of Superphosphate.

(i.) A little superphosphate is moistened with
water and tested with blue litmus paper. It will
be found to be strongly acid; hence it should not
be employed on sour or acid soils, or indeed on those
deficient in calcium carbonate.

(ii.) Some superphosphate is shaken with water
in a test-tube, the liquid filtered free from insoluble
matter, and the clear filtrate tested for phosphate with
nitric acid and ammonium molybdate.

Superphosphate contains a large percentage of its
phosphate in the water-soluble form, hence is quick in
its action. It is not washed out of soils by rain, being
retained by constituents of the soil.

Basic slag is a by-product in the removal of phosphorus
from iron in the manufacture of steel.

EXPERIMENT 24. Examination of Basic Slag.

(i.) Some slag is rubbed between the fingers. It
should be an impalpable powder, otherwise it is too
slow in action.

(ii.) Some basic slag is moistened with water and
tested with red litmus paper. It will be found to be
alkaline in reaction, a condition due to the presence
of free lime; hence basic slag is of especial value
on sour, acid land.

28 MANURES AND FERTILISERS [CHAP.

(iii.) Some slag is shaken up with water, the
solution filtered, and the filtrate tested for phosphate
as usual. It will be found that there is no water-
soluble phosphate, hence the fertiliser is not so
quick in its action as is superphosphate.

(iv.) A small quantity is shaken up with dilute
citric acid solution, and after filtering, the solution
tested for phosphate, a good indication of which
will be obtained. The phosphate is therefore not
entirely insoluble, although it does not dissolve in
water.

Practically all the potash fertilisers on the market are
derived from the natural salt deposits at Stassfurt in Germany.
Kainit, the commonest in use, is marketed as mined, but
sulphate of potash and muriate of potash are prepared by
methods of crystallisation of the natural salts.

EXPERIMENT 25. Examination of Kainit.

(i.) A sample of kainit is examined, and the
different coloured particles picked out and placed
together in small heaps. It will be evident that
kainit is not a pure salt but a mixture; in fact, it
contains sulphates, chlorides, salts of soda and lime,
as well as of potash.

(ii.) The presence of sulphates, chlorides, lime, and
potash should be demonstrated by the chemical tests
that have been described.

Kainit cannot be employed as a fertiliser for potatoes if it
be applied immediately before the " seed " is sown, as the

ill.] SULPHATE OF POTASH 29

chlorides it contains have the effect of rendering the tubers of
bad quality and waxy in texture ; for the same reason, muriate
of potash is even worse, and for application at the time
of sowing, sulphate of potash alone can be employed. The
use of the cheaper kainit is, however, possible if it be applied
some months before sowing, as the chlorides are then washed
away, while the potash is retained as carbonate by the soil.

EXPERIMENT 26. Examination of Sulphate
of Potash, K2SO4.

The pure white colour of the salt is noticed,
indicative of the fact that this fertiliser is a pure
chemical compound and not a mixture, as is kainit.
When tested for chlorides by nitric acid and silver
nitrate, only the slightest opalescence should be
obtained.

Incompatible Mixtures. A soil often requires manuring with
regard to more than one constituent, and it is convenient to
mix the separate fertilisers. Certain of the substances
mentioned above cannot be left in contact without undergoing
a loss of valuable constituents, and care should be taken
not to make a mixture of fertilisers that deteriorates in this
way.

EXPERIMENT 27. Superphosphate and Nitrate
of Soda (or Nitrate of Lime).

Equal parts of nitrate of soda and superphosphate
are well mixed, placed in a stoppered bottle, and
allowed to stand overnight. If the air in the bottle
be tested with moist blue litmus paper next day,
it will be found to be distinctly acid. This acidity

30 MANURES AND FERTILISERS [CHAP.

is due to the production of free nitric acid, the
evolution of which naturally results in the loss of
part of the fertilising constituent (nitrate) of the
nitrate of soda.

EXPERIMENT 27. Basic Slag and Sulphate
of Ammonia.

A test similar to the last is carried out with these
two fertilisers, a piece of red litmus paper being
employed. The alkalinity detected is due to the
volatilisation of ammonia liberated by the action of
the free lime in the basic slag. (Similarly, lime or
chalk and sulphate of ammonia should not be mixed
in practice.)

Lime and chalk, although not direct plant foods, are largely
used for the treatment of soil, and should doubtless be more
frequently applied than is often the case. The beneficial
effect of these substances is due to several different actions : —
(i.) Neutralisation of acidity, especially in those soils that tend
to become sour after repeated heavy dressings of dung ; (ii.)
a favouring of the growth of the nitrifying and other bacteria
in soils ; (iii.) liberation of insoluble potash compounds,
especially in heavy clay soils ; (iv.) improvement in the
texture of heavy land. Although both lime and chalk act
similarly, the former should not be brought into contact with
plants, owing to its caustic nature, but should only be applied
to soil which is at the moment fallow.

EXPERIMENT 29. Examination of Lime.

(i.) A sample of lime is sprinkled with a little
water, when a considerable rise in temperature

IIL] LIME 31

should be noticed, and the lime should swell up and
fall to powder. This phenomenon is due to the
slaking of the lime, and the quality of the latter
can be roughly gauged from the vigour of the action,
poor or " grey " limes showing practically no change.

CaO + H2O = CaH2O2

(Quicklime) (Slaked lime)

(ii.) A small quantity of the lime is boiled with
strong hydrochloric acid in a test-tube. The greater
the undissolved residue, the poorer the quality of the
lime.

(iii.) Some lime is exposed to the air for about
twenty-four hours, is then placed in a test-tube and
treated with dilute hydrochloric acid. The effer-
vescence noticed is due to the fact that the lime has
been converted into chalk by absorption of the
carbon dioxide of the air. CaO + CO2 = CaCO3.
This action of course takes place in the field when
lime is applied, and it might be thought that it
would be more economical to employ, in the first
instance, the cheaper chalk. This is not entirely so,
however, as (i) the cost of carriage of lime is cheaper
than for an equivalent quantity of chalk ; (2) the lime
on slaking falls to a fine powder which is much more
easily distributed than chalk, unless the latter be
finely ground ; (3) lime exerts a certain sterilising
action on harmful organisms in the soil, a property
not possessed by chalk.

CHAPTER IV

CHEMISTRY OF SPRAYS AND WASHES

WASHES and sprays of various compositions are used largely
for combating the different insect and fungous pests from
which fruit trees, flowers, and vegetables are liable to suffer.
The sprays in general use may be conveniently considered in
the following classes : —

Insecticides. — (a) Toxic washes for caterpillars and other
biting-mouthed insects. Arsenic in some form or another is
the poisonous constituent of most of these sprays.

(6) Contact washes for aphides and other sucking-mouthed
insects. As these insects live on the sap of the plants, they
are naturally not poisoned by treating the plants superficially
with toxic washes, and have to be dealt with by the use of
sprays that either block up their breathing pores and act as
corrosives (e.g. soft soap, paraffin) or exert a poisonous action
on their bodies (e.g. nicotine). Quassia is also employed for
the sake of the astringent and cleansing properties it possesses.

(c) Winter washes of caustic alkali for use on dormant
wood. The hibernating quarters of many insects are thus
removed.

Fungicides. — (d) Various copper compounds.

(2) Sulphur, either in the free form (flowers of sulphur) or
else combined (liver of sulphur, lime-sulphur).

82

CHAP, iv.] LEAD ARSENATE WASH 33

EXPERIMENT 30. Preparation of Lead Ar senate
Wash.

In 100 c.c. of water is dissolved \ gram of
anhydrous sodium arsenate or J gram of the crystal-
line salt, and in another 100 c.c. water is dissolved i
gram of lead acetate (sugar of lead). The latter
solution is then slowly added to the former with
constant stirring, when a precipitation of insoluble
lead arsenate in a finely divided form takes place.

2Na3AsO4+ s(CH3 . COO)2Pb

= Pb3(AsO4)2+6CH3.COONa

(Lead arsenate)

The wash so prepared when sprayed on to the
leaves will rapidly kill caterpillars, but containing as
it does both soluble arsenic and free acetic acid, may
produce a certain amount of scorching of the foliage
in some cases.

(For making the wash in quantity, use 2 ozs.
anhydrous or 3| ozs. crystalline sodium arsenate to 5
gallons water, and 7 ozs. lead acetate to another 5
gallons, and mix as directed.)

Soft soap is used alone in solution for combating the
attacks of various insects such as aphides, while it is also
employed in conjunction with nicotine and quassia in many
cases, giving greater adherence to the sprays. It is also
valuable for diminishing the surface-tension of water in the
preparation of paraffin emulsions, and a permanent emulsion
of paraffin can be prepared for use when required by melting

E

34 SPRAYS AND WASHES [CHAP.

together soft soap and paraffin to give a paraffin jelly in which
the oil is in the form of an emulsion.

EXPERIMENT 31. Determination of Lathering
Power of Soap.

The value of soap when used either alone or in
conjunction with other substances depends upon
its lathering power, a property which varies both
with the quality of the soap and the hardness of
the water used. Five grams of soft soap are dissolved
in dilute alcohol, and made up to 500 c.c. with dis-
tilled water. Fifty cubic centimetres of tap water
are placed in a flask, and a few cubic centimetres of
the soap solution run in from a burette. On shak-
ing, no lather will generally be produced, the soap
having been precipitated in the form of a curd by the
calcium and magnesium compounds in the water.
More soap solution is then added, the mixture being
well shaken after each addition, and the procedure
repeated until a permanent lather is formed. The
volume of soap solution required to produce the
lather is then noted.

The lathering power of soap with any certain
water is generally given in pounds of soap required
to produce a permanent lather with 100 gallons of
water ; this value can be calculated from the number
of cubic centimetres of soap solution required in the
above titration, thus :—

Suppose 20 c.c. soap solution were required to
produce a lather. Then 20 c.c. soap solution = -2

iv.] PARAFFIN EMULSION 35

grams soap, for 5 grams of soap are present in 500
c.c. of the soap solution prepared.
Hence -2 grams soap lather with

50 c.c. = 50 grams tap water,

therefore -2 x 20 ( = 4) grams soap lather with
50 x 20 = i coo grams tap water ;

or, expressed in pounds,

1000 Ibs. tap water require 4 Ibs. soap,
100 gallons tap water require 4 Ibs. soap.

It may be generally stated that with a water of 16-
20 degrees of hardness (a medium hard water), a
good soap should be found to have a lathering power
of from 3 \ to 4.

As stated above, paraffin has a distinct insecticidal value,
but cannot be applied in the concentrated form. It will not
dissolve in water, but can be made to form an emulsion,
especially in the presence of soap.

EXPERIMENT 32. Preparation of Paraffin
Soft- Soap Emulsion.

Thirty-five grams of soft soap are dissolved in i litre
of water in a suitable vessel, and TOO c.c. of paraffin
poured on to the surface of the liquid. By means of
an ordinary garden syringe, with a "rose" nozzle
containing a large number of fine openings, the
paraffin layer and some of the water is sucked up,
and then forced vigorously into the bulk of the liquid.
This operation is performed several times, in fact

36 SPRAYS AND WASHES [CHAP.

until there is no visible oily layer on the surface.
The emulsion so prepared will contain the paraffin
suspended in extremely small globules in the body
of the soap solution. The emulsion cannot be kept,
as the paraffin will gradually rise to the surface.

(For the preparation of the emulsion in quantity,
take water, 10 gallons; soap, 3^ Ibs. ; paraffin, i
gallon.)

EXPERIMENT 33. Preparation of Paraffin Jelly.

Fifty cubic centimetres of paraffin and 8 grams soft
soap are placed in a beaker, which is then covered
with a plate of glass. The covered beaker and its
contents are heated until the mixture boils, and i c.c.
of water is then poured in. On cooling, the liquid
becomes a jelly, of which i gram is taken and stirred
with 40 c.c. of water. The jelly will readily dissolve
to give a liquid suitable for spraying, and, as the jelly
will keep for any length of time, furnishes a con-
venient means of preparing an emulsion at short
notice for treatment of red spider, aphis, etc.

(For preparation in quantity, 5 gallons paraffin, 8
Ibs. soft soap, i pint water when boiling. For use,
10 Ibs. jelly to 40 gallons water.)

"Bordeaux mixture" is a copper fungicide that is very
largely used. Its method of preparation is due to the fact that
the copper must be obtained in the form of an insoluble precipi-
tate of sufficient fineness not to settle rapidly nor to clog the
fine nozzle of the spraying machine. The presence in the mix-
ture of any soluble copper results in a scorching of the foliage.

iv.] BORDEAUX MIXTURE 37

EXPERIMENT 34. Preparation of Bordeaux Mixture.

Eight grams of crystallised copper sulphate are
dissolved in 500 c.c. water, and the same weight of
quicklime is shaken up with an equal volume of
water. The copper sulphate solution is then
gradually added to the other solution with con-
stant stirring, and the mixture poured into a tall gas
jar or measuring cylinder. The blue precipitate of
basic copper sulphate will gradually fall to the
bottom, and the longer this settling takes, the more
satisfactory may be regarded the preparation.

A few cubic centimetres of the supernatant liquid
are filtered, and the filtrate tested for soluble copper
by adding some potassium ferrocyanide solution.
The production of a chocolate precipitate must be
regarded as unsatisfactory, as indicating the presence
of soluble copper compounds.

(For preparation in quantity, 4 Ibs. copper sulphate
in 25 gallons water, and 4 Ibs. quicklime in 25 gallons
water.)

" Lime-sulphur " is a new fungicidal wash of American origin
which is undergoing extensive trials in this country. The
sulphur is in a completely soluble form, but after spraying is
deposited in a very finely divided condition which has the
advantage over flowers of sulphur in that it is not washed off.
The successful application of the wash so as to avoid a certain
amount of damage demands, however, a considerable amount
of skill.

38 SPRAYS AND WASHES [CHAP iv.

EXPERIMENT 35. Preparation of " Lime- Sulphur"

Wash.

One hundred c.c. of water are placed in a litre
flask or other vessel, and 50 grams of quicklime
added. After well mixing, 100 grams of flowers of
sulphur are added, and the whole stirred to a thin
homogeneous paste. Four hundred c.c. of water are
then poured into the mixture, and the solution
boiled for half an hour. The orange-red liquid, con-
sisting of a solution of polysulphides of calcium,
contains a certain amount of undissolved sulphur
and impurities from the lime, and should be filtered
through cloth. The concentrated wash so obtained
must not be exposed to the air, but should be kept
in closed bottles until required. Before use, the
stock solution is diluted with twenty or forty times
its volume of water according to the variety of plant
to be treated, the dilute solutions so obtained
possessing specific quantities of i-oi and 1-005
respectively.

(For preparation of stock solution in quantity, 10
gallons water, 48 Ibs. quicklime, 96 Ibs. flowers of
sulphur ; mix, and add 40 gallons water.)

APPENDIX

IN most cases, the solutions mentioned in the text are
prepared of any convenient concentration, and need be
made of no especial strength.

Special reagents, which are required of certain definite
concentrations, should be made according to the follow-
ing directions : —

Fehling's solution should be made in the form of two
solutions, which are mixed in equal volumes for use as
required.

Solution A. 17.32 grams copper sulphate dissolved in
150 c.c. water, and the cold solution made up to 250 c.c.

Solution B. 35 grams stick caustic soda and 90 grams
sodium potassium tartrate (Rochelle salt) dissolved in
150 c.c. water, and the cold solution made up to 250 c.c.

Iodine in potassium iodide solution. 5 grams potassium
iodide dissolved in 100 c.c. water and J gram iodine
added.

Schweizer^s reagent consists of an ammoniacal solution
of cupric hydroxide. 10 grams copper sulphate are dis-
solved in 200 c.c. water, a little ammonium chloride
solution added, and then caustic soda solution in
sufficient amount just to precipitate all the copper as
copper hydroxide. The precipitate is collected on a
piece of linen, well washed with cold water, and squeezed
as dry as possible. The copper hydroxide so obtained is

40 APPENDIX

then added to a mixture of I part strong ammonia
solution and 3 parts water until no more of the
hydroxide dissolves.

Syrupy caustic soda is prepared by dissolving successive
quantities of solid caustic soda in water until the solution
so obtained is quite viscous and treacly in consistency.

Sodium cobaltinitrite solution is prepared by dissolving
a little of the salt in water as required. The solution
deteriorates on keeping.

Diphenylamine in sulphuric acid is made by dissolving
sufficient of the solid in pure nitrate-free sulphuric acid,
so that a few drops of the solution obtained give a dis-
tinct milkiness when added to i c.c. distilled water.

PU1NTKD BY OLIVKB AND BOYD, EDINBURGH

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