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Walter Scott Hendrixon.

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with the wash bottle catching the water as it runs off, or to wrap the
ends with cotton or filter paper and keep it saturated with water.




Fig. 15.



40 LABORATORY MANUAL OF GENERAL CHEMISTRY

Using loose plugs of asbestos fiber or steel wool ^confine near the
middle of the tube about 15 grams of granular iron pyrite. Connect
the outer end of the tube with the compressed air system. If this is
not available a bulb pump, foot-bellows or even a bicycle pump may be
used to force through the air. Instead of forcing through the air the
other end of the apparatus may be connected with the exhaust
system or a filtering pump.

Place in the test tube 3 c.c. of con. nitric acid, preferably fuming
acid, and to the larger bottle, connected with it add about 5 c.c. of
water. The smaller bottle contains a solution of sodium hydroxide to
absorb the excess of noxious gases,

Heat the tube containing the pyrite, preferably with a wing burner
and force or draw through a moderate stream of air. When the bot-
tles are filled with white fumes it may be known that the pyrite is oxi-
dizing. Moderate the heat to avoid distilling off unburned sulfur, and
regulate the air so that only a small amount of fumes escape from the
smaller bottle. Continue the operation 10 to 20 minutes. To avoid
sucking back remove the air connection and then the burner.

Transfer the liquids in the test tube and larger bottle to a
weighed porcelain dish, rinse with a little water and add this to the
dish. With a free flame evaporate till the steam and nitric acid va-
por give place to the dense gray fumes of sulfuric acid. Let the dish
cool and weigh it. Three to four grams of con. acid should be made in
a 10 minutes run. Show that the acid will carbonize a splinter dipped
into it. Dilute a few drops of it and test with barium chloride. Re-
move and examine the contents of the ignition tube. What results
from burning iron pyrite in air?

73. Sodium Sullite ami Thiosulfate: Dissolve 10 grams anhydrous
sodium carbonate in 50 c.c. of water with aid of heat if necessary, cool
and place just one half of the volume in a large test tube. Pass into
the solution in tube sulfur dioxide made by heating in a flask with
thistle tube 25 grams of copper turnings with 25 cc. of concentrated
sulfuric acid. The delivery tube should reach to the bottom of the
test tube. When the flow of gas begins the heat should be reduced so
as to avoid a too rapid stream. As the carbon dioxide is set free the
liquid shows a tendency to froth. The reaction is completed in about
15 minutes when small bubbles disappear, the sulfur dioxide appar-
ently is no longer absorbed, and the liquid smells strongly of the gas.
The result is acid sodium sulfite. Now add this solution to the re-
served half of the sodium carbonate solution which will give normal
sodium sulfite. Why? Place the combined solutions in a dish and boil
for two or three minutes. If evaporated nearly to dryness on a water
bath and allowed to cool crystals of sodium sulfite would be obtained.
The whole of the salt may, however, be converted into sodium thiosul-



LABORATORY MANUAL OF GENERAL CHEMISTRY 41

fate. For .this purpose add to the solution three grams of powdered
sulfur and boil gently for twenty minutes replacing from time to time
the water evaporated. Filter off the sulfur and evaporate the filtrate
over a water bath till crystals begin to form and let the solution be-
come cold.

Pour off the solution from the crystals and use it to study the
properties of sodium thiosulfate.

To a small volume of a solution of iodine add the solution of thio-
sulfate till the iodine solution is decolorized.

Make a little silver chloride by adding a few drops of a solution
of some chloride to a few drops of silver nitrate. Now add the thio-
sulfate solution, a little at a time with shaking, till the silver chloride
dissolves. What is the use of sodium thiosulfate, "hypo," in photo-
graphy ?

To the remainder of the solution of thiosulfate add an excess of
dilute hydrochloric acid, warm and note the precipitation of sulfur
and the odor of sulfur dioxide. Account for the gas and the sulfur.

Here as elsewhere study the experiment with aid of a reference
book till all is clear and write the equations.

PHOSPHORUS.

70: ..White and Red Phosphorus, Allotropic Forms: (Caution:
Handle white phosphorus only with the forceps. Keep trace of all
pieces used and any remaining must not be left about the laboratory
desk or thrown in waste jars, but put into a vessel of water provided
for that purpose).

Place a piece of white phosphorus as large as a*grain of wheat in
water in a test tube and boil. Phosphorus vapor goes off with the
water vapor but burns Jo oxide on reaching the air. Try red phos-
phorus in the same way. Does it volatilize?

Heat a little red P in a dry narrow test tube and note sublimate
of white P on wall of tube. Change white P to red P by dropping a
small crystal of iodine upon white P in a dry test tube and warming.

Dissolve a little white P in about 3 c.c. of carbon disulfide in a dry
test tube, pour the liquid upon filter paper, place this upon the ring
of a retort stand and let dry. Try to dissolve red P in a little carbon
disulfide. Do not have a flame near carbon disulfide. What is meant
by "allotropic forms"?

"7. Phosphine: Drop a piece of fresh calcium phosphide into a
small bottle or beaker full of water. The gas set free is mainly phos-
phine, PH 3 , but it is mixed with another hydride, P 2 H 4 , which takes fire
spontaneously.

78. (Caution: The following experiment is a beautiful one, but
it is attended with some danger. It may be undertaken by a small



42 LABORATORY MANUAL OF GENERAL CHEMISTRY

class under constant supervision) . Set up apparatus as in the prepara-
tion of nitrogen, but place the end of delivery tube in a dish of water,
fig. 12. Place in the flask about 20 cc. of sodium hydroxide, made by
dissolving the solid in three times its weight of water. Add two or
three small bits of white P, then about 1 c.c. of ether having no flame
near, stopper the flask and heat. When the gas begins to ignite on
reaching the air, moderate the heat so as to maintain a rate of one
bubble every two or three seconds. Carefully insert the delivery tube
into a test tube of alcohol by which the P 2 H 4 is dissolved. Does the es-
caping gas now take fire?

When cold carefully remove the stopper, fill flask with water, wash
the remaining P and place in vessel of water provided.

79. Chlorides of Phosphorus and Hydrolysis. Refer to 34, 63. In
a dish place one drop of water and add one drop of phosphorus tri-
chloride, best from a dropping bottle. What acid gas is given off?
What acid of P remains? In another dish place about the same amount
of water and phosphorus pentachloride of about the bulk of a pea,
handling it with the spatula. What gas is here given off? Save the
liquid to test for phosphoric acid in the next experiment.

80. Tests for the Radical P0 4 and Phosphoric Acids: (a) To a

few c.c. of sodium phosphate add one-fourth its volume of ammonium
chloride, make alkaline with ammonia and then add magnesium sul-
fate. The slowly forming precipitate is ammonium magnesium phos-
phate, (NH 4 ) Mg P0 4 , and this is a good test for phosphoric acid pro-
vided arsenic acid is not present. Add water to the second dish in the
preceding experiment, boil, transfer to a test tube and test for PO 4 .

(b) To test for phosphate in a substance insoluble in water dis-
solve a small portion in dilute nitric acid, and to a few drops of the
solution add twice its volume of ammonium molybdate and warm. A
yellow precipitate shows phosphate, provided arsenic acid is known to
be absent. If practicable secure a piece of bone, place it in dilute ni-
tric acid, and near the end of the period test the solution for phos-
phate by this method.

(c) To solutions of sodium phosphate HNa 2 PO 4 and "microcosmic
salt, NH 4 HNaP0 4 , add silver nitrate. Note color of precipitate the
same in both cases and try its solubility by adding to one tube dilute
nitric acid and to the other an excess of ammonia.

81. Other Acids of Phosphorus: In a crucible heat a small
amount of ordinary solid sodium phosphate and after the water of
crystallization has been driven off continue with full flame for five



LABORATORY MANUAL OF GENERAL CHEMISTRY 43

minutes. When cold dissolve some of the fused mass and test with
silver nitrate. The ordinary sodium phosphate, Na 2 HPO 4 has been
changed to sodium pyrophosphate, NaiPaOi. Repeat this experi-
ment using microcosmic salt. While the water is evaporating
test for ammonia with turmeric paper, and note odor. This salt is
changed by heating to sodium metaphosphate, NaPOs, at high tempera-
ture. Let the crucible cool, dissolve most of the metaphosphate and
test with silver nitrate. Compare the silver tests for phosphate, pyro-
phosphate and meta-phosphate.

ARSENIC.

S2. Acidify strongly with dilute HC1, dilute solutions of sodium
arsenite NasAsOj and arsenate NasAsO4 and without heating pass into
each H 2 S, for a few moments. Do you get a precipitate in the second
solution? Now heat each nearly to boiling and pass in the gas again
till the precipitation is complete. Filter on 3 the arsenic sulfide, As 2 S^,
and wash it on the filter. Try to dissolve a part of the substance in
con. HC1 in a dish. Now, boiling only gently add very small bits of
potassium chlorate from time to time till nearly all the 1 sulfide is dis-
solved. Add a little more con. HC1 to replace that boiled away, if ne-
cessary. Make alkaline with ammonia the solution in the dish and fil-
ter, and to the filtrate add a solution of magnesium sulfate or chlo-
ride. Compare this test for arsenate with that in the next section, and
with the test for phosphoric acid. (80a.)

Remove most of the remaining sulfide to a clean dish, add about o
c.c. of ammonium sulfide and heat but do not boil. This is a method of
separating arsenic sulfide from many other sulfides. To the solution
add an excess of dilute HC1 which will reprecipitate the arsenic sulfide
together with some sulfur.

83. Treat dilute solutions of sodium arsenite and arsenate with
silver nitrate and note carefully the colors of the precipitates. Try
the solubility of portions of each with dilute nitric acid and with am-
monia. Treat a solution of the sodium arsenate with ammonium chlo-
ride, make alkaline with ammonia and add a solution of 'a magnesium
salt. Compare the precipitate with that obtained in (82) in the same
way and also under phosphoric acid. How may an arsenate be dis-
tinguished from a phosphate? Given a mixture of arsenate and phos-
phate how could you remove the AsO 4 and test for the PO 4 ?

84. Tests for Small Amounts of Arsenic: One of the following
may be used:



44



LABORATORY MANUAL OF GENERAL CHEMISTRY




Fig. 16.



(a) The Modified Gutzeit Test: Good filter
paper should be wet with a solution of mercuric
chloride, allowed to dry, and cut into strips
narrow enough to slip into the horizontal tube, fig.
16. An arsenic solution containing 0.01 mg. per
c.c. and another containing 1 mg. per c.c. is made
up for class use. On no account should ordinary
arsenic solutions be used in this or the next, (b).

Place a strip of the pap*kr in the tube, and about
10 grams of coarsely granulated zinc in the bottle,
and add 15 c.c. of dilute HC1 with an equal volume
of water. After a little time look to see whether
the paper shows by brownish color that the mater-
ials used contain arsenic, and if not add 5 c.c. of
the arsenic solution of 0.01 mg. of arsenic. Let
stand 20 minutes and observe color of paper.

(b) Set up apparatus as in fig. 17, the outer section of delivery
tube being of hard glass. Place in flask 10 grams pure zinc and add

pure dilute sulfuric acid.
When air is expelled light
the gas with a test tube.
Now heat the tube and add

f~7 5 c.c. of the solution mark-

^ ed .01 mg of arsenic to 1

c.c. After several minutes
examine arsenic mirror
beyond the heated por-
tion. Move flame toward
mirror. Is the latter easily
volatilized? Now remove
lamp and add to flask 5
c.c. of the solution marked
1 mg. of arsenic to 1
c.c. Hold in the flame a

porcelain evaporating dish

Fig. 17. or crucible lid. Examine

the spots of arsenic form-
ed, and try the action of a solution of sodium hypochlorite upon them.
Antimony also gives a similar mirror and spots, but it is not soluble in
the hypochlorite.

85. If desired to use either of the tests for arsenic for practical
purposes, prepare five standard papers or five standard tubes con-
taining .01, .02, .03, .04 .05, mg. of arsenic by using 1, 2, 3, 4 and 5 c.c.
of the solution containing .01 mg to 1 c.c.




LABORATORY MANUAL OF GENERAL CHEMISTRY 45

Now cut a piece of highly-colored wall-paper for example, one
decimeter square, tear into bits, place in a dish, heat with 5 c.c. con.
sulfuric acid, until the paper is completely charred. Let cool, treat
contents of dish with 25 c.c. of water, stir well and filter. Test the
solution for As as above, using only so much as necessary to obtain a
mirror or paper containing .01 to .05 mg. of arsenic. Compare with
standards, and calculate the amounts of As to one sq. meter of wall
paper. A similar proceeding will suffice for cotton fabric.

AtfTIMOXY.

86. Heat about 0.5 gram of finely powdered antimony with about
10 c.c. con. HC1. Does it dissolve? Now add to the test tube about 1
c.c. of con. HNO 3 , being careful that the liquid does not froth over on
the hand. When most of the metal is dissolved pour a little of the so-
lution into test tube of water, and another portion into a solution of
salt. Compare the precipitate of antimony oxy-chloride SbOCl in the
two tubes, allowing for salt which may precipitate in the second tube
and quickly settle. Add con. HC1 to the first tube till the precipitate
just dissolves, and pass an excess of H 2 S into the two solutions. Also
pass the gas into solutions of tin chloride and bismuth chloride. Fil-
ter off the precipitated antimony sulfide and wash on filter. Remove a
little of the precipitate Sb 2 S 3 to a dish and boil with a little con. HC1.
How may antimony be separated from arsenic? See 82.

Dissolve a portion of the sulfides of antimony and tin by warming
in a dish with yellow ammonium sulfide, and try to dissolve bismuth
sulfide in the same way. To the solutions of Sb and Sn sulfides add an
excess of dilute HC1 when the sulfides will be reprecipitated. How
may antimony, arsenic and tin in solution be separated from bismuth
and most other heavy metals?

To illustrate the separation of antimony and tin dissolve their sul-
fides together in hot con. HC1, boil for a few moments, dilute the so-
lution with twice its volume of water, put in "card teeth" or steel wool
and boil persistently. Filter off the black scales of Sb and to the fil-
trate 'add a solution of mercuric chloride. A white precipitate of mer-
curous chloride shows stannous chloride, SnCl 2 , was present. Dissolve
the black scales on the filter with a very little aqua regia, dilute with
20 times its volume of water and pass in H 2 S which will precipitate
antimony sulfide.

CARBOff.

87. In a test-tube held in a clamp with its mouth slightly lower
than the other end, heat a block of wood. Light the gas given off and
let any liquid distilled fall into a vessel not worth cleaning. Examine



46 LABORATORY MANUAL OF GENERAL CHEMISTRY

liquid and test for acid. When the volatile products cease to come off
examine the charcoal left in tube as to its form, structure, lightness.

In a small flask boil solutions of litmus, cochineal, and indigo with
powdered bone charcoal and filter. Use about 3 g. fresh charcoal with
25 c.c. of each solution. If any one of the filtrates is not clear return
it to the flask, boil again and filter.

90. Preparation of Carbon Dioxide: Provide a bottle or flask

with thistle tube and two-piece delivery tube as in 68. Put in 25-50
grams of, calcium carbonate, cover it and the tip of thistle tube with
water, and add a little con. HC1 from time to time to maintain a mod-
erate flow of COv. Three or four jars of gas may be collected in the
same way as chlorine.

Now pass the gas into a test tube half full of clear lime water till
the precipitate of normal calcium carbonate, CaCOs, formed at first
completely dissolves as it is changed into the acid carbonate, H 2 Ca
(CO 3 ) 2 . Reverse the reaction by boiling one half of the solution. To
the other lialf add lime water which will 'precipitate the normal car-
bonate. (See 116).

Pass CO 2 into 5 c.c. 3-normal sodium hydroxide, slowly enough to
make absorption apparent. Na 2 CO 3 is formed at first, but later the acid
carbonate, HNaCOs, which being sparingly soluble, is precipitated. Re-
verse the reaction to the Na 2 CO 3 by boiling. Test a few drops of the
solution and also small amounts of other carbonates for carbon diox-
ide thus : Place a little of the carbonate in one test tube 'and a few c.c.
clear lime water in a larger one. Add an excess of dil. HC1 to the car-
bonate a,nd pour the gas set free, but no liquid, into the lime water,
shielding the mouths of the tubes from air currents as shown in lec-
ture room. A white precipitate in the lime water shows carbon diox-
ide and a carbonate.

91. Introduce into a jar of carbon dioxide rapidly burning phos-
phorus. Place a bit of burning candle in a beaker and pour carbon
dioxide upon it from a jar. Which is more dense, CO 2 or air?

Determine whether a candle v/ill burn in the exhaled breath by
filling the lungs to capacity, exhaling through a tube into a jar, and
without delay lowering into it a bit of. burning candle.

92. Carbon dioxide may be prepared by heating acid sodium car-
bonate, "soda," or magnesite, MgCO* as in Fig. 13 but turning the de-
livery tube downward. Soda decomposes into the normal carbonate
so easily that a test tube may be used. For magnesite the iron tube
is better. In this case the reaction is similar to that in making lime
by heating CaCO 3 .

93. (a) Carbon Monoxide: Set up the apparatus as in Fig 18,
having the bottles two-thirds full of NaOH, one part of the solid to
three of water. Place in flask 20 grams oxalic acid and 40 c.c. con.



LABORATORY MANUAL OF GENERAL CHEMISTRY



47



HiS04. Prepare a tube with copper oxide as in Fig 5, if (b) is assigned.

Heat the flask so as to maintain a stream of gas slow enough to
permit the absorption in the bottles of the CO 2 which comes off with
the CO.




Fig. 18.

After a jar full of gas has come over, place delivery tube in a test-tube
of lime water. It should not become turbid. If turbid, decrease the
rate of flow. Collect two jars full of gas. Remove cover of one jar,
quickly pour in lime water, seal and shake. Burn the gas in the jar
and shake again. Apply a flame to the mouth of the other jar, add
lime water, seal and shake. What is formed by burning CO?

Disconnect flask from bottles and place its delivery tube in a test-
tube of lime water. What other gas is mixed with the carbon monox-
ide? To determine the amount of this gas fill a slender test-tube with
the mixture by displacement of air, slowly withdraw the delivery tube
and cover mouth of test tube with the wet finger. Place mouth of tube
under sodium hydroxide in porcelain dish and let it remain until the
volume of gas no longer decreases. Estimate the volume of remaining
gas as compared with the original volume of the mixture and test it
with a flame.

(b) Disconnect the delivery tube and substitute for it the tube pre-
pared with copper oxide. Support this tube on a ring, connect with a
test tube of lime water. Heat the copper oxide and pass over it a slow
stream of carbon monoxide. Use more oxalic acid in the generating
flask if necessary. Is the copper oxide reduced? What is formed by
its action on carbon monoxide? For the great importance of this pro-



48 LABORATORY MANUAL OF GENERAL CHEMISTRY

perty of carbon monoxide see the chemistry of the blast furnace in the
text book.

94. Methane, Marsh Gas: Mix intimately in a mortar 10 grams of
fused sodium acetate CH 3 C0 2 Na and 10 grams of soda lime. Place in a
retort of gas pipe, provided with a two-piece delivery tube and heat as
in the preparation of oxygen, collecting two jars of gas. Light the gas
and study the degree of luminosity of the flame. Hold the. flame under
the mouth of a dry bottle or jar and note appearance of moisture. Put
lime water in the jar and shake. Pass the gas through lime water in
a test tube. What evidence have you that methane contains hy-
drogen and carbon?

To the other jar of CH 4 add a little bromine water and shake. Does
methane absorb bromine?

95. Acetylene: Cuprous chloride is required, and should be
freshly prepared as in 126. For the prepaartion of acetylene fit up the
apparatus in Fig. 10, but substitute a small flask for the test tube.
Place in flask about 10 grams of calcium carbide, and by means of the
funnel and clamp let in upon the carbide water, a few drops at a time.
When the air has been expelled as shown by collecting and burning a
test tube of the acetylene, collect three bottles of the gas. Insert the
delivery tube into a solution of cuprous chloride made alkaline with
ammonium hydroxide. The red precipitate is cuprous acetylide, Cu 2 C:>.
In the same way precipitate silver acetylide from a solution of silver
nitrate made alkaline with ammonia. These acetylides are explosive
and should be washed into the sink before they become dry.

Insert the delivery tube into a test tube half full of bromine water
and let the gas run for several minutes. Also, shake in one of the bot-
tles a little bromine water with acetylene. Compare its action on bro-
mine to that of methane.

Uncover one bottle of gas, wait a moment, then apply a flame. Why
is there a bright flash followed by quiet combustion giving a very
smoky flame?

96. Flame. Regulate a Bunsen burner so as to produce a small
slightly luminous flame. Observe the three parts, lower and inner por-
tion which is non-luminous, luminous portion, outer non-luminous por-
tion. Compare with a candle flame. With a short piece of glass tub-
ing draw off gas from lower part of flame and burn it at the end of
the tube. Try the same with candle flame. Hold a piece of wire gauze
in candle flame just above the wick and observe interior. Can you light
unburned gas above the gauze? Hold a piece of paper for an instant
in the same position and examine under surface. Repeat experiments
with gauze and paper using the flame of a Bunsen burner. Also turn
on gas, hold gauze close to the burner tube and light gas above gauze.
Now move gauze to one side.



LABORATORY MANUAL OF GENERAL CHEMISTRY 49

97. Oxidizing and Reducing Flames. Regulate a burner so as to
produce a small luminous flame, and find by trial the best position
for tip of blowpipe to produce a long slender blowpipe flame with
well-marked inner blue reducing and the outer non-luminous, oxidizing
portions.

Make a cavity with butt of pliers or a small coin in a piece of char-
coal, place in it a small quantity of lead oxide and heat in the reduc-
ing flame of the blowpipe. Continue until a globule of lead remains.
Caution: After using charcoal with the blowpipe always extinguish
any fire by holding it under the faucet and then return it to the char-
coal tray.

98. Fermentation of Glucose. In a 500 cc. flask dissolve 25 grams
of glucose, 1 gram each of sodium-potassium tartrate, ammonium nitrate
and soclic phosfate in about 250 cc. of hydrant water. Rub with a little
water in a mortar one-tenth of a cake of yeast and wash into flask.
Connect the flask with a gas washing bottle nearly full of clear lime
water, set in a warm place and let remain three or four days. Observe
from time to time the carbon dioxide given off. Take out a drop of the
liquid, place on a slide, cover and examine for cells of the yeast plant
with a microscope.

Arrange the flask as in fig. 6 and distill off 20 c.c. keeping dis-
tillate well cooled. Clean the flask, put in the 20 c.c. and distill off
about 5 c.c. Test this second distillate for alcohol, first testing for it
in a known solution as follows: to about 5 c.c. water add about 1 c.c.
alcohol and a few crystals of iodine, and shake. Warm the tube and
add gradually a solution of sodium carbonate till the iodine disappears,
lodoform will appear, at any rate on cooling. Let a few drops cool on
a watch glass and examine with the low power of a microscope. . Now
examine for alcohol the distillate above.

99. Reducing Power of Sugars. Invert Sugar. Fehling's solution


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