Ira Remsen.

A laboratory manual containing directions for a course of experiments in general chemistry systematiclly arranged to accompany the author's Elements of chemistry online

. (page 5 of 6)
Online LibraryIra RemsenA laboratory manual containing directions for a course of experiments in general chemistry systematiclly arranged to accompany the author's Elements of chemistry → online text (page 5 of 6)
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pour off some of the clear solution.

What takes place when some of the solution is ex-
posed to the air ?

When the gases from the lungs are passed through it?

When carbon dioxide is passed through it ?

What takes place when dilute sulphuric acid is
added to lime-water ?

Is calcium sulphate difficultly or easily soluble in
water?

Has lime-water an alkaline reaction ?

What reaction would you expect to take place be-
tween lime and nitric acid ?



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CALCIUM.
Experiment 98.

Gypsum ; porcelain crucible ; barium chloride.

1. Heat some powdered gypsum in a porcelain
crucible, using as small a flame as.will cause water to
be given off".

2. Examine what is left and see whether it will be-
come solid when mixed with a little water so as to
form a paste.

3. See whether gypsum itself will act in the same
way with water.

Explain what you have done.

4. Make a solution of calcium sulphate by letting
about 50 c.cm. of water stand in contact with 3-4
grams of powdered gypsum.

The presence of a sulphate in solution can be de-
tected by the same reaction as that used in the case of
sulphuric acid.

What is this reaction ?

5. See whether calcium sulphate' is in the solution
prepared under 4.



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COPPER
Experiment 99.

Copper sulphate ; strip of zinc ; strip of sheet-iron.

1. Into a solution of 2 or 3 grams of copper sulphate
in 15-20 c.cm. of water insert a strip of zinc.

Explain what takes place ?

Compare the action with that which takes place
when zinc acts upon sulphuric acid.

2. Perform a similar experiment, using a strip of
sheet-iron instead of zinc.

Compare this with the previous experiment.

Experiment 100.

Copper sulphate ; caustic soda or potash.

1. Add some caustic soda or potash to a small
quantity of a cold solution of copper sulphate in a
test-tube.

What do you notice ?

2. After noticing the appearance of the precipitate
first formed, heat.

What change takes place ?

Explain this.

Express the chemical change by the proper equation.

* For test- tube experiments use a solution containing about 10
grams of either caustic soda or potash id 100 c.cm. water. Add 5-10
drops of such a solution to a solution uf copper sulphate prepared
by adding 5-10 drops of such a solution as that used in Exp. 99 to
8-10 com. water.



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COPPER.

EXPEKIMENT 101.

Copper sulphate ; hydrochloric acid ; hydrogen sulphide ; dilute
nitric acid ; ammonia.

1. Prepare a dilute solution of copper sulphate (see
note to Exp. 100), and add to it 5-10 drops of dilute
hydrocljoric acid.

2. Pass hydrogen sulphide through this solution for
some time.

The insoluble substance formed is copper sulphide,
CuS.

3. Filter and wash. Treat with 5-10 c.cm. dilute
nitric acid, and then add 5-10 c.cm. water. What is
in the solution thus formed ?

4. Add ammonia to 1-2 c.cm. of this solution.
How could you detect copper ?



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SILVER

EXPEBIMEHT 102.

bnver coin ; dilute nitric acid ; common salt ; filter ; porcelain
crucible ; small piece of sheet-zinc ; dilute sulphuric acid ;
evaporating-dish ; water-bath ; bottle wrapped in dark paper.

1. Dissolve a ten or twenty-five cent piece in dilute
nitric acid.

What action takes place ?

2. Dilute the solution to 200 to 300 c.cm. with water.
What is the color of the solution ?

What does this indicate ?

Does this color prove that copper is present ?

3. Add a solution of common salt (prepared by add-
ing 100 ccm. water to 15-20 grams of salt and filtering
after the salt has dissolved) until it ceases to produce
a precipitate.

What change takes place ?

4. Filter off the white silver chloride and carefully
wash with hot water.

5. Dry the precipitate on the filter, by putting the
funnel with the filter and precipitate in a warm place.

6. Remove the precipitate from the filter and put it
into a porcelain crucible. Heat gently with a small
flame until the chloride is melted.

7. Cut out a piece of sheet-zinc large enough to
cover the silver chloride. Lay it on the silver chlo-
ride. Now add 15-20 drops of water and 4r-5 drops
of dilute sulphuric acid, and let the whole stand for
twenty-four hours.

What takes place ?

8. Take out the piece of zinc and wash the silver
with a little dilute sulphuric acid, and then with water.

9. Dissolve the silver in dilute nitric acid and evap-
orate to dryness on the water-bath, so that the excess
of nitric acid is driven off. Dissolve the residue in
water, and put the solution either in a bottle of dark
glass or one wrapped in dark paper.

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SILVER.
Experiment 103.

Solution of silver nitrate prepared in last experiment ; test-tubes;
sodium chloride; potassium bromide; potassium iodide; ammonia.

1. To 8-10 cubic centimeters of water in a test-tube
add 5 to 10 drops of the solution of silver nitrate just
prepared.

2. To this dilute solution add a few drops of a solu-
tion of sodium chloride.

What takes place ?

3. Place it aside where the light can shine upon it,
and notice the change of color which gradually takes
place.

4 In the same way make the bromide by adding
potassium bromide, and the iodide by adding potas-
sium iodide to silver nitrate.

What extensive practical use is made of the change
produced in silver salts by light ?

5. Try the effect of adding a few drops of a solution
of ammonia to each of the test-tubes used in 4. (Use
the solution prepared in Exp. 41.)

What differences do you notice ?

Given hydrochloric acid or common salt, how could
you distinguish between a silver salt and a copper
salt?



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IRON.

EXPEBIKEHT 104.

Iron wire ; dilute hydrochloric acid ; solution of sodium hydroxide ;
concentrated nitric acid.

1. Dissolve three or four pieces of iron wire, each
an inch or two long, in 8-10 c.cm. dilute hydrochloric
acid in a test-tube.

What is given off?
What is the cause of the odor ?
What remains undissolved ?
What is in solution ?

Write the equation representing the action of the
acid on the iron.

2. To four or five drops of the solution in 8-10 ccm.
water in a test-tube add at once as many drops of .a
dilute solution of sodium hydroxide.

What is the chemical change ?
Compare with Experiment 100.
Write the equation.

3. Let the tube with its contents stand open, and
shake it up from time to time.

What changes do you notice ?

Explain what you have seen.

4 Prepare a dilute solution of ferrous chloride as
iu 2, and heat to boiling ; then add a few drops of
concentrated nitric acid, and boil again. Repeat this
two or three times.

What change in color takes place ?

What is now in solution ?



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EXPEMMENT 104— (Continued).

5. Add four or five drops of sodium hydroxide to
the solution.

What is the chemical change ?

Compare the precipitate with that in the tube which
you have put aside (see 3).

How could you pass back from ferric to ferrous
chloride ?



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CHROMIUM.
Experiment 105.

Potassium dichroraate ; potassium hydroxide ; evaporating-dish ;
water-bath ; dilute nitric acid.

1. To a solution of 10 to 20 grams potassium
dichromate slowly add a solution of potassium hy-
droxide* until the color has turned pure yellow.
Evaporate to crystallization.

What is the product?
Explain the change ?

2. To the solution of the yellow salt just obtained
add dilute nitric acid until the color has turned red*
Evaporate to crystallization.

What is the product ?
Explain the change ?

Experiment 106.

Potassium chromate ; potassium dichromate ; hydrochloric acid ;
test-tubes.

Treat a gram of potassium chromate and a gram of
potassium dichromate separately in test-tubes with
hydrochloric acid.

Explain what takes place.

* Prepared as recommended in foot-note to Exp. 100.



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CHROMIUM.
Experiment 107.

Potassium chromate or dicbromate ; barium chloride ; lead acetate
or nitrate ; potassium or sodium sulphate.

1. Add a little of a solution of potassium chromate
or dichromate to a solution of barium chloride, and
to a solution of lead acetate or nitrate.

Explain what takes place.

2. Do the same thing using potassium or sodium
sulphate instead of potassium chromate.

How do the results compare with those obtained
with the chromate ?

Compare the composition of potassium chromate
with that of potassium sulphate.

What resemblance is there ?

* The solutions here referred to are prepared by dissolving 1 part
of each salt in 10-15 parts of water. Of such solutions use only
5-10 drops in 8-10 c.cm. water in a test-tube.



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EXPEBIMENT 108.

Potassium dicbromate; dilute hydrochloric acid; alcohol; ammonia ;
ammonium sulphide ; sodium hydroxide.

1. To 5-10 c.cm. of a solution of potassium dichro-
mate (see note to Exp. 107) in a test-tube add 10-15
drops of hydrochloric acid and 10-15 drops of alcohol,
and boil. What change takes place ?

[Under the conditions the chromium is changed to
ehromic chloride, CrCl„ and the potassium to potas-
sium chloride, while some of the oxygen of the di-
chromate acts upon the alcohol, converting it into al-
dehyde :

K a Cr,0 7 + 8HC1 = 2KC1 + 2CrCl 8 + 4H a O-f 30 ;
3C,H 6 + 30 = 3C a H 4 + 3H a O.]

Alcohol. Aldehyde.

2. To 10-15 drops of the solution of chromic chlo-
ride obtained in 1 add 5-10 ccm. water, and then add
a few drops of ammonia and of ammonium sulphide.*

Chromium does not form a sulphide, but, under the
conditions named, the hydroxide, Cr(OH)„ is precipi-
tated.

3. To a little of the dilute solution of chromic chlo-
ride (same strength as in 2) in a test-tube add a few
drops of a cold solution of sodium hydroxide.

The precipitate first formed is chromic hydroxide.

4. Add more of the solution of sodium hydroxide.
The salt NaCrO, is soluble in water.

[Cr (OH). + NaOH = NaCrO, + 2H,0.]
How could you detect chromium ?

* To prepare ammonium sulphide pass hydrogen sulphide gas into
50-100 c.cm. of a water solution of ammonia, as obtained in Exp. 41,
until the gas is no longer absorbed, and then add an equal volume
of the same solution of ammonia. The solution has a disagreeable
smell, and blackens the skin.



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LEAD.
Experiment 109.*

Lead acetate ; acetic acid ; wide-mouthed bottle ; strip sheet-zinc.

Dissolve 30-40 grams lead acetate (sugar of lead) in
a liter of water, add a few drops of acetic acid, and
put the solution in a wide-mouthed bottle. Suspend
a piece of sheet-zinc in the middle of the solution, Lnd
let it stand for a day or two.

Describe what has taken place.

Compare with the action of zinc on copper sulphate.

Compare with the action of iron on sulphuric acid.

Give the equations expressing each of the reactions
referred to.

* It will be best for the teacher to perform this experiment and
then set the vessel aside. Sometimes the lead-tree formed is very
beautiful.



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LEAD.
Experiment 110.

Sheet-lead ; shallow dish or plate ; hydrochloric acid ; sulphuric
acid ; hydrogen sulphide ; lead acetate ; piece of iron ; potas-
sium ferrocyauide.

1. Out a piece of sheet-lead an inch or two square
and partly cover it with water in a shallow dish. Al-
low it to stand for several days, renewing the- water
from time to time. Then filter oft and examine the
solution to see whether there is any lead in solution.

(a) To 8-10 c.cm. of the solution in a test-tube add
2-3 drops of hydrochloric acid.

Is a precipitate formed ?

(b) To another small portion of the solution add a
few drops of sulphuric acid.

Is a precipitate formed ?

(c) Into a third portion pass a little hydrogen sul-
phide.

What takes place?

(d) Try the same experiments with a very dilute so-
lution of lead acetate, prepared by dissolving a piece
the size of a small pea in 8-10 c.cm. water.

Of what practical importance is the above experi-
ment?

2. Try the same experiment with a piece of iron.

Is there any iron in solution ? [The easiest way to
find this out is to add a few drops of a solution of po-
tassium ferrocyanide * or yellow prussiate of potash,
when, if iron is in solution, a blue color will be seen.]

* See Experiment 8.



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LEAD.
Experiment 111.

Minium or red lead ; dilute nitric acid.

Treat a gram or two of minium with 8-10 c.cm.
ordinary dilute nitric acid in a test-tube, and note the
change in color.

Does lead pass into solution ?

How do you know ?

Experiment 112.

Lead peroxide ; dilute hydrochloric acid.

Treat a gram or two of lead peroxide with 8-10 ccm,
dilute hydrochloric acid in a test-tube.

In what form is the lead after the experiment ?
Is the product soluble or insoluble in water?



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FERMENTATION.
Experiment 113.

Apparatus as shown in Fig. 24 ; commercial grape-sugar or table-
syrup ; fresh brewer's yenst ; lime-water ; potassium hydroxide*

Dissolve 20 to 30 grams commercial grape-sugar, or
20 to 30 ccm. table syrup, in 1 to 2 liters of water in a

flask. Connect the flask
by means of a bent glass
tube with a cylinder or




bottle containing clear
lime-water. The vessel
containing the lime-water
must be provided with a
Fia24 - cork with two holes.

Through one of these passes the tube from the fer-
mentation-flask ; through the other a tube connecting
with a vessel containing solid caustic potash, the ob-
ject of which is to prevent the air from acting upon
the lime-water. The arrangement of the apparatus is
shown in Fig. 24. Now add to the solution of grape-
sugar or syrup some fresh brewer's yeast ; close the
connections and allow to stand.
What changes take place ?
Explain all you have seen.



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SOAP.
Experiment 114.

Small iron pot ; lard ; sodium hydroxide ; common salt.

1. In a small iron pot boil for an hour or two an
ounce or two of lard with a solution of 20 grams caustic
soda or sodium hydroxide in 250 c.cm. water. After
cooling add a concentrated solution of common salt.

Explain what takes place.
What is the product ?

2. Dissolve some of the product in water.



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HARD WATER.
Experiment 115.

Carbon dioxide gas ; lime-water ; solution of soap.

1. Make some hard water by passing carbon diox-
ide through 200-300 c.cm. lime-water until the pre-
cipitate first formed has dissolved again. Filter.

2. Make a solution of soap by shaking up a few
shavings of soap with water. Filter.

3. Add the solution of soap to the hard water.
Is a precipitate formed ?

4. Rub a piece of soap between the hands wet with
the hard water.

Explain what you observe.

Experiment 116.

Powdered gypsum ; bard water made as in last experiment.

Make some hard water by shaking a liter or two of
water with two or three grams of powdered gypsum.
Perform with it the same experiments as those first
performed with the water containing calcium car-
bonate.



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TANNIC ACID.
Experiment 117.

Powdered nutgalls ; ferrous sulphate.

1. Boil 10 grams of powdered nutgalls with 60 c.cm.
water, adding water from time to time. A solution
of tannin is thus obtained. Filter after standing.

2. In a test-tube add to 8-10 ccm. of this solution
a few drops of a solution of copperas (ferrous sul-
phate).

What is formed ?



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PEEPAEATION OF SOLUTIONS.

For the work now to be done various solutions will
be needed. The preparation of most of these has
already been described. For the others observe the
same general rules. In case of a solid, dissolve 1 part
in 10 parts water, and in working with this solution
in test-tubes use only 5-10 drops diluted with 8-10
c.cm. water. In some cases it may be necessary to
use more concentrated solutions. Whenever a solu-
tion, for the preparation of which the general rules
will not suffice, is referred to after this, the method of
preparation will be described. Whenever the direct
tion is given to " add a little," add a few drops of the
dilute solution at first and if, for any reason, it ap-
pears desirable to add more, do so, and note the ef*
feci



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CHLORIDES.

Experiment 118.

1. Determine which of the chlorides are insoluble
or difficultly soluble in water.

This you can do by adding hydrochloric acid or a
solution of some soluble chloride, as sodium chloride,
to a solution of a soluble salt of the element you wish
to experiment upon. Thus, for example, suppose you
wish to know whether copper chloride is soluble or
insoluble in water. You know that copper sulphate
is soluble in water, as you have worked with its solu-
tion. If copper chloride is insoluble in water, then
on adding hydrochloric acid or a solution of sodium
chloride to the solution of copper sulphate, a precipi-
tate of copper chloride will be formed.

2. In your experiments use salts of potassium, cal-
cium, magnesium, zinc, copper, mercury (both mer-
curic and mercurous * salts), silver, aluminium, iron
(both ferrous and ferric salts), manganese, chromium,
lead, and tin. Which are the insoluble chlorides ?

3. Try the action of sulphuric acid on several chlo-
rides. What is given off? How do you know ?

* A solution of mercurous nitrate, HgN0 8l is prepared by treating
a small globule of mercury the size of a pea with 4-5 cm. dilute ni-
tric acid. The quantity of acid should not be sufficient to dissolve
all the mercury. Dilute the solution thus obtained with 5-10 times
its bulk of water.



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NITKATES.

EXPEBMENT 119.

1. Determine which of the nitrates are insoluble or
difficultly soluble in water.

Work in the same way as with the chlorides.

2. Try the action of sulphuric acid on several ni-
trates.

What is given off ?
How do you know ?

3. Heat some nitrates to a high temperature in a
crucible.

What takes place ?

How could you distinguish between a chloride and
a nitrate, if both were soluble ?



Experiment 120.

1. Determine which of the sulphates are insoluble
or difficultly soluble in water ?

Which are they ?

2. Try the action of hydrochloric and of nitric acid
on some sulphates.

Do you notice any change ?

How could you distinguish between a chloride, a
nitrate, and a sulphate ?
See Experiments 79 and 98.



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CARBONATES.

Experiment 121.

1. Determine which of the carbonates are insoluble
or difficultly soluble in water. After having obtained
a precipitate, determine whether it is a carbonate or
not by filtering, and treating the washed precipitate
with hydrochloric acid.

Which carbonates are difficultly soluble or insoluble
in water ?

Which salts give, with a soluble carbonate, precipi-
tates which are not carbonates ?

2. Try the action of hydrochloric, of nitric, and of
sulphuric acid on several carbonates.

What is given off?
How do you know ?



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SULPHIDES.

Experiment 122.

1. Determine with which metals hydrogen sulphide
forms insoluble sulphides, by making solutions con-
taining salts of the different metals, and passing hy-
drogen sulphide through them successively.

Which are the insoluble sulphides ?

2. Prepare solutions of salts of the same metals
used in 1, and add a little hydrochloric acid to each.
Then pass hydrogen sulphide through those solutions
with which hydrochloric acid does not give precipi-
tates.

With which ones does hydrogen sulphide give pre-
cipitates ?

3. To those solutions with which hydrogen sulphide
does not give precipitates add ammonium sulphide.

Which solutions give precipitates with ammonium
sulphide ?



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HOW TO ANALYZE SUBSTANCES.

In order to analyze substances chemists make use
of reactions like those you have studied in Experi-
ments 118, 119, 120, 121, and 122. To learn to analyze
complicated substances, long practice and careful
study of a great many facts are necessary. But simple
substances can be analyzed by the aid of such facts
as you have already learned. You have learned, for
example, that certain chlorides are insoluble in
water ; that certain sulphides are insoluble in dilute
hydrochloric acid; and that other sulphides which
are soluble in dilute hydrochloric acid are insoluble
in neutral or alkaline solutions. Advantage is taken
of these and other similar facts to classify substances
according to their reactions. A convenient classifica-
tion for purposes of analysis is the following :

Group I. Metals whose chlorides are insoluble or dif-
ficultly soluble in water. This group includes:
Silver, lead, and mercury in mercurous salts.

Group II. Metals not included in Group I, whose
sulphides are insoluble in dilute hydrochloric or
nitric acid. This group includes : Copper, mer-
cury (as mercuric salt), bismuth, antimony, arsenic,
and tin.



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Group III. Metals not included in Groups I and II,
whose sulphides are precipitated by ammonium
sulphide and ammonia. This group includes :
Aluminium, chromium, nickel, cobalt, iron, zinc, and
manganese.

Group IV. Metals not included in Groups I, II, and III,
which are precipitated by ammonium carbonate,
ammonia, and ammonium chloride. This group
includes : Barium, strontium, and calcium.

Group V. Metals not included in Groups I, II, III,
and IV, which are precipitated by di-sodium
phosphate, HNa a P0 4 , ammonia, and ammonium
chloride. This group includes : Magnesium.

Group VI. Metals not included in Groups I, II, III,
IV, and V. This group includes : Sodium, po-
tassium, and ammonium.

1. Now, suppose you have a substance given you
for analysis. The first thing to do is to get the sub-
stance in solution. See whether it dissolves in water.
If it does not, try dilute hydrochloric acid. If it does
not dissolve in hydrochloric acid, try nitric acid ; and
if it does not dissolve in nitric acid, try a mixture of
nitric and hydrochloric acids. If concentrated acid
is used, evaporate to dryness on a water-bath before
proceeding further. Then dissolve in water, and add
a few drops of hydrochloric acid. If a precipitate is
formed, continue to add the acid drop by drop until a
precipitate is no longer formed. Filter and wash.

What may this precipitate contain ?

2. Pass hydrogen sulphide through the filtrate for
some time and let stand. Filter and wash.



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If a precipitate is formed, what may it contain ?

3. Add ammonia and ammonium sulphide to the
filtrate. Filter and wash.

If a precipitate is formed, what may it contain ?

4. Add ammonium carbonate, ammonia, and am-
monium chloride to the filtrate. Filter and wash.

If a precipitate is formed, what may it contain ?

5. Add di-sodium phosphate, ammonia, and am-
monium chloride to the filtrate. Filter and wash.

If a precipitate is formed, what may it contain ?
What may be in the filtrate ?



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EXAMPLES FOE PKACTICE,

Before attempting anything in the way of systematic
analysis it will be well to experiment in a more general
way, with the object of determining which one of a
given list of substances a certain specimen is.

The list below contains the names of the principal
substances with which you have thus far had directly
to deal in your work. You have handled them and
have seen how they act toward different substances.
Suppose now that a substance is given you, and you
know simply that it is one of those named in the list,
how would you go to work to find out which one it is ?
You have a right to judge by anything in the appear-
ance or in the conduct of the substance. If you reach
a conclusion, see whether you are right by further
experiments. After your work is finished write out a
clear account of what you have done, and state clearly
your reasons for the conclusion which you have
reached.

For example, suppose sodium chloride is given
you. You see it is a white solid. On heating it in


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Online LibraryIra RemsenA laboratory manual containing directions for a course of experiments in general chemistry systematiclly arranged to accompany the author's Elements of chemistry → online text (page 5 of 6)