UNIVERSITY OF CALIFORNIA DEPARTMENT OF EDUCATION GIFT OF THE PUBLISHER No./ ! may be pushed through it. Slip over one branch of the L-tube one end of a piece of rubber tubing about 30 cm - long, whose other end is slipped over a delivery tube ! ! . Set the flask on a wire gauze ] 2 on a ring of a stand and secure the neck of the flask with a second ring (Fig. 16). Alternate Apparatus. (Fig. 17.) A retort is pro- vided with a delivery tube and is supported on a ring stand over a wire gauze or sand bath 1 2 . Place the mixture in the flask or retort, and heat with a small flame, removing the flame if the evolution of the gas becomes too brisk. Collect five receivers full by water displace- ment 13 , and pass to Experiment 14. NOTE 8. To Per- forate Corks. To perforate a cork, a round ("rat-tail") file about i$cm. long is required. A cork is chosen of such a size that its narrower end fits a little loosely in the neck of the flask, retort, etc. The cork is softened in a cork squeezer or by rolling it on (i) the table top under a board ; or (2) on the floor under the sole of the shoe. The tip of the tang of the file is heated to redness and the red-hot point used to burn a small and regular hole through the axis of the cork. This hole is then enlarged with the file until the glass tube can just be passed through it by employing a twisting motion. Fig. l6 HEATING A SUBSTANCE IN A FLASK AND COLLECTING THE GAS EVOLVED Experiments Fig. 17 HEATING A SUBSTANCE IN A RETORT AND COLLECTING THE GAS EVOLVED BY WATER DISPLACEMENT Cork borers may also be used. These are tubes of brass or steel, with a cutting edge, and are of various sizes, so as to cut a hole of very nearly the desired diameter at once. NOTE 9. To Cut Glass Tubing. To cut glass tubing, a three- cornered file about 25 cm. long is needed. The tube is laid flat upon the table, and a deep scratch made with the file at the point where the tube is to be cut. The tube is then grasped with the two hands, one on each side of the scratch, while the thumbs are brought together just at the scratch, but on the side opposite. While the fingers are pulling on the tube in the direction of its length, a slight push with the thumbs across the axis of the tube usually suffices to break it squarely off. When a piece of glass tubing is cut the ends have sharp edges which may cut rubber tubing slipped over them. The edges should be smoothed down or " fire polished" by gradually heating them in a flame, all the while twirling the tubing so that the edges are heated uniformly, until the glass softens and the sharp edges become rounded off, but care should be taken that the bore of the tube is not at all lessened. NOTE 10. To Bend Tubing. To bend glass tubing, hold it in a flat luminous flame, such as that offered by an ordinary gas jet (a so-called "bat-wing," "fish-tail," or "wing-top" may be put on the Bunsen burner). Rotate the tube and move it to and fro so as to heat a portion of the tube at least ^cm. in length. When the tube begins to soften let it almost by its own weight bend around to the desired shape. Do not try to bend it suddenly or apply any considerable force. The bend should be very gradual and the bore of the tube remain unchanged in the bend. Always i8 Elementary Chemistry " fire-polish " the ends of the tube. Such a tube is often called an "L-tube," from its resemblance to the letter L. NOTE ii. Putting Apparatus Together. In putting together the parts of an apparatus, it is very necessary that they make tight joints. The corks should be well softened and the tubes inserted firmly. It is a good plan to lubricate glass tubing with glycerin, vaseline, or even water. The best way to test an apparatus for gas-tightness is either to compress the air in it by blowing or draw some out by suction. As usually some part of the apparatus is under water, the water will thereby be made to rise or fall in a tube, and if there is any leak, this water will change its level when the opening where the lips were applied is closed. To attempt to use leaky apparatus is to lose time and labor, and to insure the failure of the experiment. NOTE 12. Heat- ing Glass Vessels. In heating glass ves- sels, wire gauze (best of copper) is usually employed. Sand baths may also be used, and consist of a shallow iron dish containing a little sand. Serviceable ones may be made out of tin-pail or tin-can covers. Squares of asbestos paper are also used in many laboratories. The object of thus interposing a screen is to distribute the heat and render the glass less liable to crack. NOTE 13. Collecting Gases by Water Displacement. This method consists in filling wide-mouthed vessels brimming full of water, covering them tightly with a piece of paper, cardboard or glass, inverting them with the cover pressed against the mouth, placing them mouth downward in a dish filled with water (techni- cally named a pneumatic trough), and removing the cover. The pressure of the atmosphere keeps the water in the vessels, or receivers, as they are commonly called. Most pneumatic troughs are provided with a shelf less than an inch below the surface of the water (Fig. 17), on which the receivers are set. The gas which is evolved is made to pass up into the receiver by means of a delivery tube, and to displace the water. Only gases which are but slightly soluble in water can be col- lected by water displacement. Fig. 1 8 STOPCOCK FUNNEL GAS GENERATOR AND CYLINDER FOR COLLECTING THE GAS Experiments Fig. 19 HOME-MADE STOPCOCK FUNNEL, NO. I EXPERIMENT 13. Oxygen from Sodium Peroxid by Action of Water. Fit a dry flask (200 to 300^-) with a delivery tube and stopcock fun- nel 14 . Place about 20^- ( 7 cm - circle) of sodium peroxid in the flask and allow water to drop slowly upon it from the funnel. Collect five receivers full by water displacement 13 and pass to Ex- periment 14. NOTE 14. Gas Generators. Gas gener- ators are employed when a gas may be formed by the interaction of a solid and a liquid. Of these there are many styles, of which those provided with a stopcock funnel are the best, but stopcock funnels are expensive. A serviceable stopcock funnel may be made by the student as follows : Choose a piece of rubber tubing that will just slip into the stem of a funnel and cut off a piece about -2cm. long (Fig. 19). Cut a hole about i mm - in diameter near one end and, warming the rubber a little, rub cement (made by melting in a dish two parts of beeswax with one of rosin) around trie lower half so as to form a thin coating. Very cautiously (remember that funnels are made of thick glass and are very liable to break if heated rapidly or unevenly) warm the stem of the funnel where it commences to flare out and push the rubber tube into it. When the glass is cold the cement will hold the rubber in position very firmly. Put a little vaseline on a glass rod 15 that slips easily but snugly into the rubber tubs. To close the stopcock, push the rod down so that it may cover the lateral hole. To open it, raise the rod more or less so as to uncover more or less the hole. Such a stopcock cannot of course be used with liquids which have any action on rubber. Pick out a good cork fitting the neck of the flask (or use a rubber stopper), soften it, and perforate it with two holes, through one of which the stem of the funnel passes, and through the other one of the L-tubes, forming a delivery tube (Fig. 18). Another form of home-made stopcock funnel is the following : A funnel tube is cut off short and connected with a long piece of glass tubing by means of a bit of rubber tubing which can be closed with a pinchcock (Fig. 20). Still another form consists of an ordinary thistle or funnel tube, into the stem of which fits a bit of rubber tubing slipped over a glass rod. By pushing the rubber tube into the stem of the funnel and holding it there by the glass rod, the stopcock is closed. Fig. 20 HOME- MADE STOPCOCK FUNNEL, NO. 2 20 Elementary Chemistry EXPERIMENT 14. Properties of Oxygen. The first receiver of gas caught in the three preceding experi- ments contains the air that was in the generator and is to be rejected. Attach a piece of charcoal to a wire, heat it in a flame until it begins to glow, and then removing the glass plate from one of the receivers, insert it into the gas (Fig. 21), replacing the glass plate as far as possible. The wire may be thrust through a card so that the charcoal can be supported in the center of the receiver. Place a little sulfur in a combustion spoon 16 , set it on fire by directing a flame down upon it, and lower it into the second receiver. Put a little red phosphorus in a combustion spoon, light it thoroughly and thrust it into the last receiver. Keep the receiver covered so that the fumes cannot escape into the room. Attach a piece of picture cord wire to a stiff wire, fray out its end a little, heat it and dip it into sulfur so that some may cling to the wire. Set this on fire and at once introduce into a jar full of oxygen. To prevent the intensely hot oxid of iron which is formed from breaking the receiver, it should be a quarter full of water, or a layer of wet sand may first be put into the vessel. The object of tipping the frayed end of the cord with sulfur is to raise the temperature of the iron to the kindling point so that it too will burn. What do these experiments teach about combustion in air and in oxygen ? Fig. 21 BURNING A SUB- STANCE IN OXYGEN Experiments 21 a b c d Fig. 22 COMBUSTION SPOONS NOTE 15. Stirring Rods. To make a glass stirring rod, cut off a piece of solid glass rod of the desired length and round its ends by holding it in the flame of a Bunsen burner. Stirring rods may also be made out of tubing by heating its ends until the glass runs together and closes them up. NOTE 16. Combustion Spoons. Combustion or deflagrating spoons are little cups to hold combustible materials to be burned in a receiver of gas. Besides those procurable at the dealer in chemical apparatus (Fig. 22 a), ser- viceable ones may be improvised by (i) fastening an iron or aluminum thimble about half full of plaster of Paris (which has been mixed with water and allowed to set) to a wire handle (Fig. 22 6) ; (2) hollowing out a piece of chalk and fastening it to a wire handle (Fig. 22 c) ; and (3) twisting a wire around a bit of asbestos paper (Fig. 22 d\ OZONE EXPERIMENT 15. Preparation of Ozone. Put a few drops of ether in a small flask and cork it tightly. The ether will vaporize and a mixture of air and ether vapor will presently fill up the flask. Heat a stout glass rod to redness, and plunge it into the mixture of air and ether vapor. Smell of the product cautiously. Hold a piece of iodo-starch paper over the mouth of the flask and note any change of color. Does ether vapor alone produce any change of color ? CAUTION. Ether is very inflammable. Do not have any flames near when pouring it from a bottle. EXPERIMENT 16. (Quantitative^ To Find the Weight of One Liter of Oxygen. Put about 5^- (i cm - circle) of powdered manganese dioxid in a clean, dry evaporating dish and heat it as hot as possible for at least fifteen minutes so as to dry it thoroughly. In the meantime assemble an apparatus like that shown in 22 Elementary Chemistry Fig. 23. AB is a nine-inch test tube fitted with a two- hole rubber stopper. Through one hole passes a short bit of glass tubing over which a rubber hose provided with a Hofmann cock or pinchcock is slipped ; through the other passes an L-tube, the shorter branch of which fits into the two-hole stopper of an aspirating bottle 17 . The aspirating bottle, D, is filled full of water, and , an " acid bottle, " about half full of Fig. 23 APPARATUS FOR FINDING THE WEIGHT OF A LITER OF OXYGEN temperature of the room. Take about 20^- (5 cm - circle) of dry potassium chlorate and mix it on a piece of smooth paper with the manganese dioxid, which should still be warm. Transfer the mixture to the test tube, which has been previously thoroughly dried, wipe out any dust that may cling to the upper part of the tube, and insert just below the stopper a loose plug of glass wool or a coiled strip of previously ignited asbestos paper, its object being to prevent the oxygen from car- rying off any solid particles in passing from the tube. Experimen ts 23 Weigh the test tube and contents to a centigram as soon as possible after rilling. Holding the tube horizontally, tap it gently so as to make the mixture spread out and lie along the tube, and connect with the aspirating bottle, the tube being supported on a ring of a retort stand. Opening the clips at F and at H (use clip at //), force water into E by blowing at F, so as to drive all air from the long rubber tube. Then by suction draw water back into D until its level reaches nearly to the stopper, raise E so that the water in D and in E is at the same level, and close F tightly. Close H and very cautiously remove the rubber tube from E in such a manner that no water escapes from the tube. Empty the water out of E and drain it for a few seconds. Then place the end of the rubber tube in E and open the clip at H. A little water will flow out because the level in D is higher than that in , but there should not be a continual flow, as that would indicate that the apparatus was leaky. With a small flame gently heat the test tube, begin- ning near its mouth. If the mixture begins to froth at the point heated, heat another portion of it. The flame must not be held steadily at one place, but played to and fro through a distance of about 3 cm -. The glass should not be heated red-hot, as there is then danger of a hole being blown through it. When the "acid bottle" is about three-quarters full, discontinue the heating and let the apparatus stand until it cools to the temperature of the room. In the meanwhile read the barometer. Then lift E up or down (it can be lowered by bringing it down over the side of the table), hold it so that the level of the water remains the same for a minute or so in both bottles, always keeping the end of the rubber tube under water, and close the cock at H. Elementary Chemistry Disconnect the test tube and weigh it again. The difference between this weight and the one previously found is the weight of the oxygen evolved. Remove R without disturbing the water in the rubber tube, and measure the volume of water it con- tains by pouring it out into graduated vessels (Appen- dix BY or by weighing it on a platform balance and subsequently weighing the empty and drained bottle. Take the temperature of the water and reduce the volume of the oxygen to standard conditions. If this reduced volume be denoted by v and if the weight of the oxygen be denoted by zv, the weight of a liter may be computed by means of the pro- portion : v : iv :: 1,000 : x The accepted value for the weight of a liter of oxygen is 1.43^-. What possible sources of error can you point out in the determination of your value ? NOTE 17. Aspirators. A large bottle, Z>, is fitted with a two-hole stopper carry- ing two L-tubes (Fig. 24). A rubber tube a little longer than the bottle is slipped over the outlet tube and may be closed with a pinchcock, //. To aspirate a gas, fill the bottle with water, insert the stopper with its tubes, connect the inlet tube with the apparatus furnishing the gas, B ', remove the pinchcock, start the water flowing so that as it goes out the gas may be drawn into the bottle. Aspirating bottles may also be used to store gases ; when the bottle is full of a gas, slip a bit of rubber tubing over the inlet tube and close it with a pinchcock, and then close the outlet tube. The gas may be forced out by connecting the aspirator with a second one filled with water and placed at a higher level. The water may be made to siphon over from the second bottle into the first, thus expelling the gas. The gas may also be driven out at B by connecting the outlet tube with the water supply of the laboratory. FlR. 24 ARRANGEMENT OF TUBES IN AN ASPIRATING BOTTLE Experiments EXPERIMENT 17. (Quantitative^) To Find the Per- centage of Oxygen in Potassium Chlorate. Clean and dry a porcelain crucible and cover, place upon a pipestem triangle (Fig. 25), and heat gently at first so as not to break the cru- cible, and then as hot as possible for two or three minutes. When the crucible is cool, weigh it to a centi- gram (Appendix B}. Put about 1.5^. (2. circle) of dry pow- dered potassium chlo- rate in the crucible and weigh again. Place the covered crucible on the tri- angle and heat with a Fi 8- 25 HEATING IN A PORCELAIN CRUCIBLE flame about 5 cm - high, which just reaches to the bottom of the crucible. Lift the cover up from time to time with the forceps and regulate the flame so that the melted potassium chlorate is seen to give off its oxygen but slowly. If any should spatter up on the cover, remove the flame, place the cover bottom side upper- most on a clean piece of smooth paper, and with a pin loosen the layer of chlorate and return it to the cruci- ble, being very careful that none is lost. When the bubbling is seen to slacken, increase the size of the flame, and finally heat for ten minutes with a flame large enough to reach to the top of the crucible when its yellow spot is just below the bottom of the crucible. Let cool and weigh, 26 Elementary Chemistry Again heat very hot for about five minutes, and cool and weigh as before. If the weight does not change, pass to the calculations. If the weight is less, heat again, and continue in this way until two successive weights are the same. This operation is called heating to constant weight. The loss of weight is equal to that of the oxygen. The percentage of oxygen in the chlorate is calculated thus: Weight of potass, chlorate : weight of oxygen : : 100 : x The accepted value for the percentage of oxygen in potassium chlorate is 39.2. What is the percentage of error in your result ? Point out any sources of error. Fig. 26 GAS GENERATOR, PNEUMATIC TROUGH, AND RECEIVERS HYDROGEN EXPERIMENT 18. Hydrogen from Acids by Action of Zinc. Arrange a gas generator as shown in Fig. 26. A wide-mouthed bottle is fitted with a two-hole stopper (best of rubber), through which pass a funnel tube 18 and an L-tube. A piece of rubber tubing connects the L-tube with a second one, thus forming a delivery tube. Experiments 27 Cover the bottom of the bottle with granulated zinc, fit in the stopper, push the funnel tube down so that it nearly touches the bottom of the bottle, and run in through the funnel tube enough water to just cover, and thus seal its end. Pour dilute sulfuric or concentrated hydrochloric acid 19 through the funnel so as to cause a brisk evolution of gas, and after testing its purity 20 , collect four receivers full by water displacement and pass to Experiment 19. As an alternate apparatus a stopcock funnel gener- ator (Fig. 1 8) may be used. Zinc is placed in the bot- tle, covered with water, and strong hydrochloric acid dropped in just fast enough to make the gas come off briskly. NOTE 18. Funnel Tubes. Funnel tubes are tubes of glass with one end flared out to form a funnel, or they may be described as small funnels with long stems. The style shown in Fig. 26 is sometimes called a " thistle tube," from its fancied resemblance to the head of a thistle A funnel tube should always have its lower end dip below the liquid in a generator so as to seal it. NOTE 19. To Moderate Action of an Acid. If hydrochloric acid is used and so much is introduced into the generator that hydrogen is given off too rapidly, a little water poured through the funnel will dilute the acid and thus moderate its action. CAUTION. Hydrogen mixed with air is very explosive. NOTE 20. Testing Hydrogen. Never perform experiments with hydrogen until you have convinced yourself that the hydrogen is free from air in the following way : Fill a small test tube with the gas by water displacement. Place the thumb over the mouth of the test tube while it is still under water and, bringing it close to a flame, open it so that the gas may pass into the flame (Fig 27). If the gas ignites with an almost inaudible report, it is pure ; if with a loud report, or sharp whistle, it is mixed with air. Continue to gener- ate the gas until it is pure before collecting it. Fig. 27 DISCHARGING GAS FROM A TEST TUBE INTO A FLAME 28 Elementary CJieviistry EXPERIMENT 19. Properties of Hydrogen. Hold- ing a receiver full of hydrogen in an inverted position (Fig. 28), thrust a lighted splinter up into the gas and then very slowly remove it. Does hydrogen burn ? If so, what is the appearance of its flame ? Set a receiver full of hydrogen, with its mouth upward, on the table, and after waiting at least three minutes, insert a blaz- ing splinter. How do you account for the result ? What property of hydrogen is hereby shown? See if you can pour hydro- gen upward. How can you make sure that hydrogen is in the upper receiver? Pressing a glass plate or a piece of cardboard tightly against the mouth of a receiver full of hy- drogen, place it in- verted upon a receiver of the same size filled with air, and slip out the plate or card (Fig. 14). After at least five minutes remove the UDDCT rCCeiVCT and . keeping it inverted, insert a lighted splinter (Fig 28). Account for the result. What general property of gases is hereby illustrated ? EXPERIMENT 20. Transpiration of Hydrogen. Hold down over the delivery tube (a straight tube is substituted for the L-tube) of a gas generator, from which hydrogen is issuing rapidly, a dry glass tube, Fig. 28 - INTRODUCING A LIGHTED SPLINTER OF WOOD INTO A GAS LIGHTER THAN AIR Experiments 29 closed at one end with a plug of plaster of Paris, with the thumb pressed over the plug-. In a few minutes slowly lift the tube up, keeping it closed with the thumb all the while, until it is clear of the delivery tube ; then dip the open end under water in a beaker or tumbler and remove the thumb (Fig. 29). Let the tube stand for at least fifteen minutes, examining it from time to time. Explain what occurs. EXPERIMENT 21. Combustion of Hydrogen. Wrap several folds of a towel over and around your gas generator so that in case of an explosion the broken glass can be prevented from flying about. Test the purity of the hydrogen 20 , which should be escaping quite rapidly, and then attach a straight glass tube drawn out to a jet 21 to the rubber tube. Ignite the hydrogen and thrust the jet up into an inverted beaker. What col- lects in the beaker ? Pinch the rubber tubing so as to extinguish the flame, dry the inside of the beaker, and as before thrust the jet with unlighted hydrogen escaping from it into the inverted beaker. What occurs ? NOTE 21. Jet Tubes. To make a jet tube, select a piece of glass tubing about i2- long and ^mm. bore with a rather thick wall. Heat the middle in a Bunsen flame, twirling it so as to heat it uni- formly. When it begins to soften, slowly draw it out as shown in Fig. 30. Cut it off at the narrowest point, and fire-polish the wider ends of the two jet tubes thus made. Fig. 2Q APPARATUS FOR SHOWING TRANSPIRATION OF A GAS Fig. 30 STAGES IN MAKING A JET TUBE 3O Elementary Chemistry EXPERIMENT 22. Oxidation and Reduction. Scrape a few bits of copper foil or wire bright and clean and put them into the middle of a glass tube about 30 cm - long. Heat the tube gently just below the copper, sup- porting it on a ring stand with interposed wire gauze, and in a slanting position so that a draft of air may pass through it. Do not heat the glass to redness. The blackening of the copper is due to the formation of copper oxid ; the copper is oxidized. Fig- 31 PASSING A GAS OVER A SUBSTANCE HEATED IN A TUBE Let the tube cool and then slipping over one end of it a delivery tube, and connecting the other end with a hydrogen generator, pass hydrogen through it (Fig. 31). After the hydrogen has been found by test to be pure, heat the copper. What does the change of color go to show ? EXPERIMENT 23. Hydrogen from Water by Action of Sodium. With dry fingers and knife cut off a piece of sodium not more than 5 mm - in diameter 22 and scrape it bright and clean. Wrap the bit of sodium up snugly in a scrap of filter paper which has been moistened in kerosene 22 , and using tongs bring it under a large test tube filled with water and inverted in a pneumatic Experiments trough. Let go of the sodium so that it may rise into the tube. If not enough gas is generated to fill the test tube, use a second piece of sodium. Lift up the tube, keeping its mouth down, and bring it to a flame. How do you know it contains hy- drogen ? NOTE 22. Sodium Must be Kept Dry. Be sure that everything that is used in handling so- dium is dry. The object of dipping the paper in kerosene is to prevent a too rapid access of the water to the metal. Too much paper should not be used, else the water will be prevented from com- ing in contact with the sodium. EXPERIMENT 24. Hydrogen from Steam by Action of Magnesium. Draw out one end of an L-tube so as to form a jet 21 and thrust the other end through a Cork fitting a Small Fig. 32 HYDROGEN FROM STEAM BY THE flask (Fig. 32). Put a little (only a pinch, for if too much is used the heat of the reaction may be so great as to break the tube) powdered magnesium in the tube and shake it down so that it lies along the branch next to the jet. Put a little water in the flask, insert the cork, and heat the water to boiling so that a moderate current of steam passes Elementary Chemistry Fig. 33 HYDROGEN FROM STEAM BY THE ACTION OP IRON through the jet. Apply a flame to the issuing- steam and see if it can be ignited. The little flashes of light are due to the burning of tiny particles of magnesium, which are caught up and carried along by the steam. With a second Bunsen flame heat all the horizontal branch of the L-tube hot enough to prevent the conden- sation of moisture in it. Then heat steadily the portion of the magnesium farthest from the jet until a reaction begins, and at once remove the flame. Can the gas now issuing from the flame be set on fire ? Compare with Experiment 21. EXPERIMENT 25. Hydrogen from Steam by Action of Iron. Place enough small brads in a piece of gas- pipe (or, better, bicycle tubing) 40 cm - to 50^- long and about 2 cm. bore, to fill the middle of the pipe for a distance of about 20 cm - f and then fasten the pipe with wire across a wide ring of a stand (Fig. 33). Attach a Experiments 33 delivery tube to one end of the pipe and to the other an L-tube, with a long pieee of rubber tubing, making connections with a second L-tube inserted in a flask supported on a second ring above the pipe. Bend a thick piece of asbestos board into a gable-roof shape and place it over the pipe. Put a little water in the flask and arrange the ring supporting it so that it nearly touches the asbestos. Heat the middle of the gaspipe as hot as possible, using two burners. Place bits of wet filter paper over the ends of the pipe and keep them dripping wet all the time so as to prevent the charring of the corks. If the water in the flask boils too vigorously, raise the ring supporting it a little. Collect some of the gas given off and test it. EXPERIMENT 26. Hydrogen from Solutions of Caustic Alkalis by Action of Aluminum. Place a few bits of aluminum in a test tube and fill it about a fourth full with caustic soda or potash solution. If effer- vescence is not very brisk, heat a little. Close the tube with the thumb, and after a minute or so open it so as to discharge the gas into a flame (Fig. 27). Account for what occurs. EXPERIMENT 27. Hydrogen from Sodium Hydroxid by Heating with Iron Powder. Make an intimate mixture in a mor- tar of i g- (6 mm -) of sodium hydroxid and 20^- (4^- circle) of iron powder, and introduce it into a hard glass test tube provided with a cork and delivery tube (Fig. 34). Fig. 34 HEATING A SUBSTANCE IN A TEST TUBE AND COLLECTING THE GAS EVOLVED 34 Elementary Chemistry Fig. 35 A COMMON FORM OF WATER BATH Supporting" the tube on wire gauze and under a ring, heat the upper part of the mixture first so as not to cause too brisk an evolution of the gas, and collect it by water displacement. EXPERIMENT 28. Hydrogen from Calcium Hydroxid (Lime) by Ac- tion of Iron Powder or Zinc Dust. Make an intimate mixture of equal volumes (2 cm - circle) of dry calcium hydroxid and iron powder, put it into a hard glass test tube provided with a cork and delivery tube, and heat, using a test tube holder, collecting the hydrogen evolved over water. Zinc dust may be used instead of iron powder in Experi- ments 27 and 28. WATER EXPERIMENT 29. Dis- solved Matter in Differ- ent Waters. Slip a small rubber band over a test tube about a third of the way from its closed end, fill it up to the band with distilled water, pour the water thus measured into a clean evaporating dish (watch glass or saucer), and evaporate to dryness on a water bath 2 3 or sand bath (asbestos board) 12 . Note the nature and Fig. 36 AN IMPROVISED WATER BATH amount of any residue. Repeat these operations with hydrant water and other natural waters which may be available. Compare natures and amounts of residues. Experiments 35 NOTE 23. Water Baths. To avoid raising the temperature of a substance above that of boiling water, water baths are used. A common form (Fig. 35) consists of a copper vessel with a cover made of a series of rings. By removing one or more of these, a dish may be set down nearly to its rim on the bath. Water is kept gently boiling in the bath so that the dish may be surrounded by steam. Care must be taken to replace from time to time the water which boils away, else the temperature will be raised too high. A serviceable water bath may be improvised with a beaker (best with a lip) and stand (Fig. 36). EXPERIMENT 30. Distillation. Fit one end of a long straight tube to a retort or to an L-tube inserted through the neck of a flask. The other end passes into a test tube set in a dish of water. Fill the flask (Fig. 37) or the retort (Fig. 38) about a third full of water and add a piece of copper sulfate (3 >>.). Boil the water in the flask gently and collect a test tube full of the distillate. It is well to cover the part of the test tube which is not under water with a piece of filter paper which is kept wet so as to aid in the condensa- tion. What is the color of the distillate ? Can copper sulfate be totally separated from water by distillation ? Fig- 37 SIMPLE DISTILLING APPARA TUS, FLASK FORM Fill an evaporating dish about a fourth full of alco- hol and set fire to it. While the alcohol is burning, add Fig 38 _ water in small portions at a time with constant stirring until the flame goes out. Clean out the retort or flask, and empty the mixture of alcohol and water into it. Distill the mixture, collecting SIMPLE DISTILLING APPARA- TUS, RETORT FORM 36 Elementary Chemistry enough of the distillate to fill the test tube about a fourth full. Pour the distillate into the evaporating dish and try to set it afire. What does your result prove about the possibility of separating alcohol and water by distillation ? Which is the more volatile, water or alco- hol ? Which has the higher boiling point ? EXPERIMENT 31. Coagulation Filters. Put a pinch of clay in a test tube and fill with water. Shake the water and clay well together and filter (Fig. 10) a por- tion of the muddy water (a suspension of clay in water). Is the filtrate clear? Filter the filtrate a second time and see if it becomes clear. Can clay and water be separated by filtration ? Now add to the muddy water a few drops of alum solution, shake up thoroughly, and filter through a fresh filter. Is the filtrate clear? If not, add a little more alum and filter again. EXPERIMENT 32. Conditions Affecting Solution. (a) fineness of Division. Choose two crystals of po- tassium dichromate, alum or copper sulfate, both just small enough to slip into a test tube, and powder one finely in a mortar. Put the crystal and the powder in separate test tubes and fill both the tubes about half full of water. Close the tubes with the thumbs and shake vigorously. In which case does solution take place the more rapidly ? In which case is the surface of contact between the solid and the liquid the larger ? To save time in dissolving a solid, what preliminary operation ought it to be subjected to ? (b) Temperature. Put about 6 - (3 cm - circle) of powdered potassium dichromate in a test tube, and fill it about a third full of water. Shake the solid and liquid well together for some time. Does the solid all dissolve? Is there a limit to the solubility of a sub- stance at a given temperature ? Heat to boiling for a minute or so. Does the solid all dissolve now ? Cool Experiments 37 the tube and contents by letting cold water run over it. What happens ? What effect has temperature upon the solubility of a substance ? EXPERIMENT 33. (Quantitative^) To Determine the Solubility of Potassium Dichromate in Water. Fill a flask (200 to 300 c - c -) a fourth full of powdered potassium dichromate, and add sufficient water to fill the flask about three-fourths full. Cork the flask tightly and place it in a pneumatic trough filled with water at the temperature of the room. Put a thermometer in the trough and read its temperature at intervals of about two minutes, and each time shake well the solid and liquid in the flask. The temperature should not vary by more than a degree for at least fifteen minutes. Filter a portion of the solution thus saturated into a weighed evaporating dish so as to fill it about half full. Weigh the evaporating dish and solution and then evaporate to dryness on a water bath 23 . Be very careful not to lose any of the solid by spurting. Let the dish and con- tents cool and again weigh. Calculate the percentage composition of the solution. EXPERIMENT 34. (Quantitative.} To Determine the Solubility of Air in Water. Shake a large bottle filled about half full of water vigorously for several minutes so as to saturate it thoroughly with air. The water should be at the temperature of the room, and care should be taken not to warm it up in shaking by the heat of the hands. Fit a small flask (200 to 300 c - c -} with a stopper (best of rubber) and a delivery tube of narrow bore (not more than 2 mm -) of the form shown in Fig. 39. Set the flask on a ring of a stand with interposed wire gauze so that its delivery tube may come under a test tube placed in a beaker set on a second ring of the same stand. Fill both the beaker and the test tube with water, invert the filled test tube in the beaker, and pour out as much Elementary Chemistry water as possible from the beaker without the water in the test tube escaping. Take the temperature of the water in the bottle and fill the flask brimful. Then insert the stopper so that the delivery tube will be filled with water also. There must not be any bub- bles of air either in the flask or the delivery tube. Weigh the flask, delivery tube, and con- tents to decigrams, set the flask upon the wire gauze so that its deliv- ery tube engages un- der the test tube, and heat with a small flame, making the water boil vigorously until a cracking sound is heard, indicating that all the air has been expelled from the water. Remove the delivery tube from the water in the beaker and stop heating. Fill the beaker with water at the temperature of the room, lift the test tube up so that the level of the water inside and outside is the same, and mark it with a small level rubber band slipped over the test tube. Remove the test tube and determine the volume of the air driven out of the water either with a burette (Appendix B) or by weighing the water which fills the tube up to the rubber band. Dry flask and delivery tube and weigh. Record results thus: Fig. 39 APPARATUS FOR DETERMINING THE SOLUBILITY OF AIR IN WATER Experiments 39 Weight of water filling flask and delivery tube = A , and after shaking out the solid mixture, fill the rubber tubing brimful of water, close it with the thumb and place the tubing under water. Now open clamp A What happens? With a rubber band or piece of cotton cord mark the volume of the gas remaining. What gas is it ? Ascer- tain the volume of this and that of the nitric oxid taken 72 Elementary Chemistry at first by running 1 in water from a burette or by weigh- ing-. What conclusion do you draw as to the volume of oxygen and nitrogen composing nitric oxid ? * EXPERIMENT 97. Nitrogen Dioxid. Heat in a test tube a few crystals of manganous nitrate, Mn(NO 3 ) 2 , or lead nitrate, Pb(NO 3 ) 2 . The main gaseous product is nitrogen peroxid. Is it soluble in water ? EXPERIMENT 98. Illustration of the Law of Vol- umetric Proportions* Prepare two gasometric tubes as follows : Obtain two test tubes about 2$ cm - long and i cm - wide. Fill the small tube even full of water and empty it into one of the large tubes, and mark the position of the water level with a rubber band. Add a second tube full and mark the position of the water level, and continue in this way until the tube is full. Proceed in like manner with the second large tube. Introduce into one of the gasometric tubes two vol- umes of nitric oxid (best prepared from nitric acid and ferrous sulfate), and into the other, five volumes of air. Pass the contents of one tube into the other. 31 What is observed ? In two or three minutes read the volume of the residual gas. What gas is formed when nitric oxid comes in contact with oxygen ? Is it soluble in water ? Explain the contraction. Repeat this procedure at least twice, so as to be sure of the results, each time transferring the residual gas into a receiver so that it may be examined and tested as follows : Measure out from the receiver three volumes and add a measured volume of air. Is there any con- traction ? If so, add some more air, and see if there is any contraction. In the same fashion, add volumes of nitric oxid to a measured volume of the residual gas and continue the additions until there is no contraction. Point out in detail how this experiment illustrates the law in question. Experiments 73 NOTE 31. Transferring Gases. To transfer gases from ne vessel into another, the pneumatic trough must be deep enough to allow of the complete submerging of the vessels. They are then placed so that the gas from one may rise and displace the water in the other. EXPERIMENT 99. Preparation and Properties of Nitric Acid. Put into a retort about 15 ff. (5 cm - circle) of powdered soditim or potassium nitrate and add about 30 c.c. of strong sul- furic acid. Arrange the apparatus (Fig. 53) so that the retort's neck passes nearly to the bottom of a test tube or flask set in a dish filled with cold water. Heat gently with interposed wire gauze, noting the be- havior of the mixture in the retort. When the test tube is about a quarter full of the distillate remove the flame ; be sure that the end of the retort's neck is not dipping below the surface of the acid in the test tube. CAUTION. Be very careful not to spill nitric acid on the hands; it produces very bad burns. Note the color of the nitric acid thus prepared, and compare it with that of a freshly-opened bottle of the commercial "c. p." article. How do you account for the difference ? Cautiously note its odor. Pour a few drops on a glass plate or watch crystal and place beside it a glass plate or watch crystal containing a little strong ammonia water. How do you account for the result ? Put a bit of litmus paper in a dish and add a few drops of acid from the test tube ; repeat after Fig. S3 PREPARING NITRIC ACID 74 Elementary Chemistry diluting the acid with about four times its volume of water. Take up a drop on a stirring" rod and touch it to your finger-nail or a quill ; wash it off promptly and put on a drop of ammonium hydroxid. Test its action both when cold and when hot on a little of the follow- ing metals placed in separate test tubes : iron, copper, zinc, lead, and mercury. Pour a drop or so into a little indigo solution. Put a drop on a piece of newspaper and on a piece of the best linen writing paper. Is the difference in the action sufficient to distinguish news- paper (which is made from wood pulp) from writing paper (which is made from Jinen rags)? What is the paper of your notebook made of, wood pulp or linen? EXPERIMENT 100. Decomposition of Nitric Acid by Heat. Support a long-stemmed tobacco pipe on a stand so that its mouthpiece just dips below the water in a dish, Heat the stem red-hot with a Bunsen flame and then pour a few drops of concentrated nitric acid into the bowl so that it may flow down through the heated portion. What makes the bubbles have a reddish-brown color while the gas which collects in the receiver is colorless ? Into what three substances is the nitric acid decomposed ? EXPERIMENT 101. Reduction of Nitric Acid to Ammonia. Put a little granulated zinc into a test tube and add about 5 c - c - of dilute sulfuric acid. After the hydrogen is escaping freely, add a drop at a time (a "medicine dropper" will be found convenient, or a little pipette easily made by drawing out to a jet a piece of glass tubing), very dilute nitric acid, noting carefully what happens when each drop is added. Add only about a dozen drops of the nitric acid. After a few minutes pour part of the solution into another test tube and add an excess of caustic soda solution. Warm a little and cautiously smell of the contents of the tube. Experimcn ts 75 What evidence is there that ammonia is being given off ? Verify your conclusion by the use of litmus paper and by Nessler's solution. How do you explain the formation of the ammonia ? EXPERIMENT 102. Reduction of a Nitrate to a Nitrite. Heat 15^- of sodium or potassium nitrate with 30^- of lead in an iron dish (sand bath pan), stirring the melted mixture with a stiff iron wire or long nail until most of the lead has disappeared. Transfer the cooled mass to a mortar, grind it to a powder, add hot water, stir well and filter. To a portion of the filtrate add a few drops of concentrated sulf uric acid, or potassium or barium nitrate. The yellowish-brown powder formed during the heating is lead oxid. What is the source of the oxygen combining with the lead ? How must the nitrate have been changed ? PREPARATION AND PROPERTIES OF ACIDS, BASES, AND SALTS EXPERIMENT 103. Preparation of a Salt (Mercury lodid) by Direct Union of the Elements. Weigh on a watch glass 2.5^- of mercury 32 , and then also on a watch glass ^.2^- of iodin 33 . Place the mercury in a clean mortar and just cover it with alcohol 34 . Add about a quarter of the iodin and rub it gently into the mercury until the iodin as such seems to have dis- appeared. Then mix in a second quarter-portion and continue until all the iodin is added and the mixture is dry and of a bright red color. Transfer the product to a test tube and add about 5 c - c - of alcohol. Heat the alcohol to boiling for a minute or so by immersing the end of the tube in boiling water contained in a beaker. Pour the solution into an evaporating dish and set aside to cool. Examine carefully the crystals of mer- cury iodid which separate out. Place a few of them 76 Elementary Chemistry in a dry test tube and cause them to sublime by heat- ing the rounded end of the tube. How do you account for the different colors of the sublimate ? Rub it with a glass rod and note any change of color 35 . NOTE 32. Pipette for Handling Mercury. A convenient way to handle small quantities of mercury is by means of a little pipette made by drawing out a piece of narrow glass tubing to a long, tapering point. Mercury is drawn up into the pipette by suction. If the tube then be held in an almost horizontal position, the mercury will not run out, and may be nicely discharged where wan ted" by inclining the pipette a little. NOTE 33. Danger of Corrosion. As both mercury and iodin corrode brass, great care must be exercised not to let them or their fumes come in contact with the brass parts of a balance. Be sure to collect any of either element whteh may become scattered about the balance through careless handling. NOTE 34. Addition of Alcohol. The reason for adding alcohol is to keep down the temperature (the heat of the reaction will be expended largely in evaporating the alcohol) and to bring the iodin and mercury in more intimate contact. The alcohol does not participate in the reaction at all. NOTE 35. Iodin Stains. Iodin stains may be removed by means of sodium sulfite or ammonium sulfid solution. EXPERIMENT 104. Preparation of a Salt (Zinc Sul- fate) by the Solution of a Metal (Zinc) in an Acid (Sulfuric). Place about 5^- of zinc in a beaker or flask and add about 40 c - c - of dilute sulfuric acid. When the evolution of hydrogen has nearly ceased, filter the solu- tion into an evaporating dish and gently heat 3 6 over a wire gauze nearly to boiling, until a thin film appears on the surface of the solution. Then set it aside so that it may cool slowly. At frequent intervals for several days examine the crystals which separate out and carefully note their form. Remove them from the solution and dry them by pressing between folds of filter paper. Do the crystals contain water of crystal- lization ? NOTE 36. Slow Evaporation. Instead of evaporating off the water rapidly by heating, the dish may be set aside so that the water may slowly evaporate during several days. If this be done, better and larger crystals will be obtained. Experiments 77 EXPERIMENT 105. Preparation of a Salt (Ammo- nium C/tlorid) by the Neutralization of Ammonium Hydroxid by Hydrochloric Acid. Dilute 25 c-c. of con- centrated hydrochloric acid with an equal vol- ume of water, mix well, and fill a burette with the mixture 3 7 . Fill a second burette with concentrated ammonium hydroxid (Fig. 54). Run 5.0^- of the acid into an evaporat- ing dish which has pre- viously been weighed to centigrams, and add just enough litmus solution to impart a distinctly pink color. Note the reading on the burette containing the ammonium hydroxid, and run the solution, a few drops at a time, into the acid, with constant stirring, until the red color turns to blue. Then run in the acid, drop by drop, stirring after each addition, until the color is half-way between blue and red. Evaporate the solu- tion to dryness on a water bath 2 2 (the ammonium chlorid volatilizes at a higher tem- perature), let cool and weigh. Again heat for a quarter of an hour and weigh, continuing in this way until the salt is perfectly dry, as shown by no further loss in weight. Fig. 54 BURETTES ARRANGED FOR NEU- TRALIZING A BASE BY AN ACID TO PRO- DUCE A SALT 78 Elementary Chemistry The equation for this neutralization reaction may be written thus : NH 4 OH + HC1 -> NH 4 C1 + H 2 O How many grams of NH 4 C1 have you prepared ? Calcu- late how much NH 4 OH and HC1 were needed. How much NH 4 OH and HC1 were contained in the volume of the solutions used? Calculate how many grams of NH 4 OH and of HC1 there would be in a liter of a solu- tion of the same concentration. NOTE 37. Drying the Burette. If the burette is not perfectly dry, it should be rinsed out, delivery tube and all, with a few cubic centimeters of the acid before filling. The ammonium hydroxid burette should also be rinsed out with that liquid. EXPERIMENT 106. The Solubility Product. Pre- pare a saturated solution of sodium chloric!, NaCl, by shaking the solid in a test tube with water until no more is dissolved. The solution will not be accelerated by heating, as sodium chlorid is nearly as soluble in cold water as in hot. Fill a test tube a quarter full with this saturated solution. Put a few cubic centi- meters of concentrated hydrochloric acid in a test tube provided with a cork and delivery tube, heat gently, and pass the hydrogen chlorid expelled from solution into the solution of salt. Prove experimentally that the white substance precipitated is sodium chlorid, and explain its formation. THE HALOGENS AND THEIR HYDROGEN COMPOUNDS EXPERIMENT 107. Chlorin by Oxidization of Hy- drochloric Acid. Into separate test tubes put a pinch of potassium chlorate, of red lead, and of potassium dichromate, and add a little strong hydrochloric acid to each. If a reaction does not take place promptly, warm a little. Note the physical properties of the gaseous Experiments 79 product, and then stop the action by filling the tube up with water. What are the color and other properties of this solution ? EXPERIMENT 108. Preparation of Chlorin. I. (Hood.) Into a flask (200 to 300 c - c -} fitted with a delivery tube and an interposed safety bottle (Fig. 55), put about 20 ff- (5^- circle) of manganese dioxid and add to it 50^- strong hydro- chloric acid. The delivery tube should reach to the bottom of the receiver, which should be snugly covered with a piece of cardboard pierced with a hole for the pas- sage of the delivery tube. Heat the flask gently and collect by downward displacement four receivers full of the gas. You can tell by the greenish color when the receivers are full, and the full receivers should be covered with glass slips smeared with a little vaseline so as to make gas-tight joints. Pass to Experiment no. EXPERIMENT 109. Preparation of Chlorin. II. (Hood.) Into a gas generator fitted with a stopcock funnel (Fig. 18) put about enough of bleaching powder to cover the bottom of the generator to a depth of a centimeter. The delivery tube should reach to the bot- tom of the receiver, which should be covered with a piece of cardboard with a hole through it for the passage of the delivery tube. Let strong hydrochloric acid drop from the funnel upon the bleaching powder just fast Fig. 55 PREPARING CHLORIN 8o Elementary Chemistry enough to keep up a brisk evolution of the gas, and col- lect four receivers full by downward displacement, cov- ering a receiver when full (as shown by the green color) with a glass slip smeared with vaseline. Pass to Ex- periment no. EXPERIMENT no. Properties of Chlorin. (Hood.) Thrust a piece of flaming paper into a receiver filled with chlorin, moving the glass slip only a little aside and at once covering the receiver again so as to prevent the fumes from escaping. Is the gas combustible? Does it support combustion ? Moving the glass slip aside again, sprinkle a pinch of powdered antimony into the gas. Also introduce a loose bundle of very fine brass or copper wires which have been heated to redness. Is the gas a supporter of combustion ? Com- pare it in this respect with oxygen. Into a second receiver put some paper with writing (both by ink and by pencil) on it and some pieces of dry calico, and into a third some paper with writing on it and some pieces of moistened calico. What differ- ences are to be observed in the bleaching action in the two receivers ? Repeat with the fourth receiver any of the above experiments, the results of which you are in doubt about and wish to verify. EXPERIMENT m. Chlorin Water. Drop into a test tube a few small crystals of potassium chlorate, cover them with concentrated hydrochloric acid diluted with an equal volume of water, warm a little, and as soon as the chlorin begins to escape from the tube, fill it nearly full of water. Pour a little indigo solution into a test tube and add an equal volume of the chlorin water. Is the color discharged ? Try the action of the chiorin water on solutions of litmus, of cochineal, and of copper sulfate. Explain any differences in the bleaching action. Experiments 81 EXPERIMENT 112. Preparation and Properties of Bromin. Put about 10^- (^ cm - circle) of potassium bromid in a mortar and add an equal bulk of man- ganese dioxid. Mix them well together and introduce the mixture into a dry retort, and then add about io c - c - of concentrated sulfur ic acid. Support the re- tort on the stand so that its neck may enter a test tube or flask set in a dish filled with cold water (Fig. 56). Put a little water in the test tube and ad- just so that the neck of the retort just dips into the water. Heat the retort very gently and collect the bromin given off until no more red vapor is seen in the retort. Note the phys- ical properties of the bromin. Pour a drop or so of bromin into a dry receiver, cover with a piece of paper or a glass slip, and shake and invert the receiver so that the bromin may rapidly vaporize and its vapors fill the vessel. Try its bleach- ing action as was done with chlorin and compare results. Pour what bromin is left into the bottle labeled "Bromin" which is standing on the side table. EXPERIMENT 113. Preparation and Properties of lodin. Grind well together in a mortar a half dozen crystals of potassium iodid with an equal bulk of man- ganese dioxid, put the mixture in an Erlenmeyer flask, and add about 15^- of a mixture of equal volumes of concentrated sulfuric acid and water. (Pour the acid 82 Elementary Chemistry into the water, not the water into the acid.) Set the flask on a wire gauze on a ring stand, and insert in its neck loosely a perforated cork holding a small test tube filled with cold water (Fig. 57). Another appara- tus is a tall, slender beaker with a watch glass cover- ing it and filled with cold water (Fig. 58). Heat the flask with a very small flame, just enough to cause the iodin liberated from the potassium iodid to vaporize and collect on the sides of the test tube kept at a low temperature by the cold water. When the test tube is covered with crystals of iodin, dis- continue the heating, re- move the test tube, and scrape the iodin into an evaporating dish. Note its physical properties. Fig. 57 PREPARING IODIN ' ln J 1 . Heat a small crystal in a dry test tube and when the tube is filled with the vapor, invert it and draw conclusions as to the relative weights of air and iodin vapor. Touch your finger to a crystal. What is the color of the stain ? Will water remove it ? Will alcohol ? Will a solution of potassium iodid? In which of these three liquids is iodin readily soluble? Place the rest of the iodin in the bottle labeled " Iodin " which is standing on the side table. EXPERIMENT 114. Tests for Free Bromin and Iodin. Prepare a test tube full of chlorin water (Ex- periment in). Dissolve a bit of potassium iodid and of potassium bromid not larger than a pinhead in a small Experiments test tube a quarter full of water, a different test tube for each substance. Make some thin starch paste by rubbing up a small lump (5 mm -) of starch with a little water in a mortar to the consistence of cream, and then boiling it in an evaporating dish with about 50^- of water until it is clear. Pour three or four drops of this starch paste into 10^- of water in a test tube and shake it up well ; then add a drop of an aqueous solution of iodin. What is the change in color? Heat the solution gently until the color disappears, and then cool it by immersing in cold water. This is a very delicate test for iodin when not in Combination. Repeat Fig. 58 ANOTHER APPARATUS FOR PREPAR- this test, using bro- min water instead of an iodin solution. Is the test as decisive as for iodin ? Pour three or four drops of starch paste into 10^- of water in a test tube, shake it up well, and add a drop or so of the solution of potassium iodid you have pre- pared. Is there any change of color ? Now add a dozen or so drops of the chlorin water. Explain what occurs. Repeat with the solution of potassium bromid instead of the iodid. Compare the results. Put a couple of drops of an aqueous solution of iodin in about io c - c - of water in a test tube, add about 84 Elementary Chemistry 2 c-c. of carbon bisulfid, and shake the two liquids well together. Does the color of the carbon bisulfid change ? Repeat, using a solution of bromin instead of iodin. Compare the two results. Repeat, using a solution of chlorin water. Does this give a decisive test ? Add about 2 c - c - of carbon bisulfid to the solution of potassium iodid prepared and shake them well together. Does the color change? Add a few drops of chlorin water and shake. What result? Repeat, using the solution of potassium bromid. Compare results. Could you prove by these tests that bromin was present in a solution of unknown composition if iodin was also pres- ent? Try it on a mixture of potassium bromid and potassium iodid solutions. EXPERIMENT 115. Action of Concentrated Sulfuric Acid on Halid Salts. Place in separate test tubes a couple of small crystals of sodium chlorid, of potassium bromid, and of potassium iodid, and add to each about 2 c - c - of concentrated sulfuric acid. Cautiously compare the smells of the gases evolved. Heat gently and note the appearance of any colored gases, if they have not been noticeable without heating. What elements are set free ? Put a pinch of calcium fluorid (fluorspar) in a small test tube and add about 2 c - c - of concentrated sulfuric acid. Heat until a gas is given off vigorously. Note the physical properties of this gas and after five min- utes or so pour out the reacting mixture into a plentiful supply of water. Wash out the test tube and see if the glass has lost its transparency in spots, and if so, account for it. To clean the test tubes pour their contents out into a large amount of water. Do not run water into tJie tubes upon the hot sulfuric acid, as there is danger of an explosion. Experiments EXPERIMENT 116. Preparation and Properties of Hydrochloric Acid. Put io c - c - of cold water in a beaker and add to it slowly and with constant stirring, SQC.C. of concentrated sulfuric acid. Set the mixture aside to cool. Put about 30^- (6 cm - circle) of common salt in a flask provided with a safety bottle and delivery tube, to the end of which may be attached a small funnel (Fig. 59) or a straight piece of large glass tub- ing. Add the cold acid and heat gently with the funnel attached to the end of the delivery tube, un- til the gas given off is nearly all absorbed by the water in which the rim of the funnel just dips. Then collect by down- ward displacement four dry receivers of the gas, cov- ering them with glass plates when full. Let the gas pass into some distilled water contained in a dish, using the funnel attachment, and save the solution for Expe- riment 1 1 8. Invert a receiver full of the gas and, holding its mouth under water in a pneumatic trough, open it. How do you account for what happens ? What other gas studied has exhibited a similar property ? Thrust a blazing splinter of wood into a second receiver. Does the gas burn or support combustion ? Hold a piece of wet filter paper over the mouth of another receiver. Fig. 59 PREPARING HYDROCHLORIC ACID 86 Elementary Chemistry What is the cause of the phenomenon? Drop in the last receiver a piece of filter paper moistened with strong" ammonia water. What happens ? What is the substance formed ? EXPERIMENT 117. Analysis of Hydrogen Chlorid. (a) Place a bit (3 ) of sodium in a bulb tube (Fig. 60), support it horizontally, and connect it on one side with a generator from which a brisk current of hydrogen chlorid (generated by dropping con- Fig. 60 sutB TUBE centrated sulfuric acid into concentrated hydrochloric acid contained in a stopcock generator) is issuing, and on 'the other with a delivery tube. As soon as all the air has been swept from the tube (How can that be told?), heat the sodium cau- tiously until it takes fire. Now collect in a test tube a sample of the gas given off and discharge it into a flame. What is the gas ? When the sodium no longer burns, disconnect the generator (letting the gas pass into water by means of a funnel, as described in Experiment 116), and, after the bulb tube has cooled, break it open and prove by appropriate tests that common salt, NaCl, has been formed. In the burning of the sodium, what substances were the combustible and the supporter of combustion, respectively ? (b) Put some manganese dioxid into an evaporating dish and heat as hot as possible for about ten minutes so as to remove all moisture from the dioxid. Arrange an apparatus . as shown in Fig. 31. Place in the tube some of the manganese dioxid and connect with the gas generator. As the hydrogen chlorid passes through the tube, heat the manganese dioxid gently by just brushing a flame along the tube. Collect the gas given off over water and establish its identity by suitable tests. Experiments 87 How do you account for the moisture that collects just beyond the dioxid ? EXPERIMENT 118. Tests for Chlorids, Bromids, and lodids. Prepare dilute solutions (about 3 per cent) of sodium chlorid, of potassium bromid, and of potas- sium iodid. To a few drops each of these solutions add an equal volume of silver nitrate solution. Compare the colors and properties of the precipitates. Boil the solutions and note the behavior of the precipitates. Add ammonium hydroxid until pieces of litmus paper placed in the tubes are blue, shake well, and note which pre- cipitates dissolve. What is the effect of adding enough nitric acid to make the litmus red ? Add silver nitrate solution to a little of the solution of hydrogen chlorid prepared in Experiment 116, and to as many chlorids, bromids, and iodids as are available. How do all the results compare ? How can a test for a fluorid be devised from Experiment 115 ? EXPERIMENT 119. {Quantitative.} To Find the Atomic Weight of Chlorin. Clean, dry, and weigh to centigrams an evaporating dish. Fill it about one- fourth full of finely powdered sodium chlorid and heat until decrepitation ceases. Let cool and weigh. Cover the salt with strong nitric acid, evaporate to dryness on a water bath, and heat with free flame until the sodium nitrate which has been formed just begins to melt. Let cool and weigh. To make sure that all the chlorin has been expelled, moisten the salt with concentrated nitric acid, heat and weigh again, repeating until a constant weight is obtained. The reaction is : NaCl + HN0 3 > NaNO 3 + HC1 A known weight (a) of sodium chlorid is converted into a known weight (6) of sodium nitrate. If the atomic weight of chlorin be denoted by .r, and those of sodium, nitrogen, and 88 Elementary Chemistry oxygen arc 23, 14, and 16, respectively, then the molecular weight of NaCl is: + ^ and that of NaNO 3 is : 23 + 14 + (3 X 16)1=85 a 23 + x Then -= b 8 85 a 23 b and x = b EXPERIMENT 120. (Quantitative^ To Ascertain the Strength of a Given Sample of Hydrochloric Acid. Fill a burette with the acid to be tested. Put about IQC-C- of a 5 per cent solution of sodium hydroxid in an evaporating dish, and add a few drops of some indicator. Run the acid into the alkali with constant stirring until neutralization is obtained. Evaporate to dryness without spattering. Heat the dish to constant weight. Calculate the weight of hydrogen chlorid in one liter of the solution. The equation for the neutralization of sodium hydroxid by hydrochloric acid is : NaOH + HC1 > NaCl + H 2 O 40 + 36.5 58-5 + 18 from which it is seen that 58. $& of NaCl are formed when 36. 5 of HC1 are used. The weight of the HC1 in the volume of the solution taken stands then in the same ratio to the weight of the NaCl found as does 36.5 to 58.5. The weight of HC1 contained in a liter of the acid solution is calculated by means of the pro- portion : Volume of acid taken inc-c. Weight of acid found 1,000 c - c - x EXPERIMENT 121. (Quantitative^] To Find the Strength of a Given Sample of Nitric Acid. The directions of Experiment 1 20 apply to rinding the strength of a given sample of nitric acid ; sodium nitrate is formed. Experiments 89 THE ALKALI METALS EXPERIMENT 122. Properties of Sodium and Potassium, (a) Examine a small piece of sodium ; note its most obvious properties, such as color, luster, and hardness. Cut a slice off it and immediately note the metallic luster. Review Experiment 23 (action of sodium on water). Cautiously dissolve a small piece in a little water in an evaporating dish. What is the action of the solution on litmus ? Evaporate to dryness and examine residue carefully. What is it ? (b) Repeat (), using" potassium. EXPERIMENT 123. Preparation and Properties of Potassium Carbonate, (a] Fill a test tube half full of hardwood ashes, cover with water, shake well together, warm gently and filter. Test the filtrate (i) with both blue and pink litmus paper, (2) for potassium (Experi- ment 127), and (3) for a carbonate (add HC1 ; a result- ing effervescence indicates CO 2 ). (b} Put about 5^- (4^- circle) of cream of tartar (acid potassium tartrate) in an iron dish and heat strongly in the hood until the residue is white. Grind the residue in a mortar with water, filter, and apply the same tests as in (a). (c) Mix thoroughly about 5^- (^ cm. circle) of pow- dered potassium nitrate with an equal bulk of powdered charcoal, and place the mixture in an evaporating dish. Heat an iron dish or plate red-hot and, standing at arm's length and grasping the evaporating dish with tongs, pour the mixture upon the iron. If it does not deflagrate at once, heat still hotter, being careful not to have your face or hands above the mixture. When deflagration has occurred and the product is cool, grind it in a mortar with a little water, filter, and test the ni- trate as in (a}. 90 Elementary Chemistry EXPERIMENT 124. Preparation and Properties of Sodium and Potassium Hydroxids. Make a solution of about 50 & (10 cm - circle) of sodium carbonate in about 300 c-c. of water and place it in an iron dish. To about 20 ff- of lime add enough water to slake it and make a milky mixture, "milk of lime." Heat the sodium car- bonate solution to gentle boiling, add the milk of lime and boil for five minutes, stirring constantly with a large nail or a file. Let the precipitate settle, draw off a little of the clear liquid with a tube drawn out so as to form a small pipette, 3 2 transfer it to a test tube and add an equal volume of dilute hydrochloric acid. If there is effervescence, all of the 'sodium carbonate has not been changed into the hydroxid ; so add a little more milk of lime and boil. If there is no effervescence, decant the clear liquid into a beaker. As sodium hydroxid attacks glass and porcelain, it is not advisable to evaporate the solution to dryness. The solution may be preserved in a rubber-stoppered bottle, labeled "Sodium Hydroxid," for use in subsequent work. Examine a piece of commercial sodium hydroxid and note its most prominent physical properties. Potassium hydroxid is to be prepared according to the same directions as given for sodium hydroxid, using potassium carbonate instead of sodium carbonate. EXPERIMENT 125. Preparation and Properties of Ammonium Amalgam. Put about 2 c - c - of mercury into a dry test tube, add a small piece (2 "**) of sodium, cork the test tube very loosely, and heat gently. As soon as a flash of light has indicated that the sodium has formed an amalgam with the mercury, introduce another piece of sodium, heat, if necessary, as before, and continue in this way until the amalgam has become solid. (An evaporating dish may be used instead of the test tube.) Experiments 91 Put about io c - c - of a strong solution of ammonium chlorid in an evaporating dish, and introduce into it about a quarter of the sodium amalgam. (The test tube will probably have to be broken to get the amal- gam out.) How does the amalgam change ? Take up some of the substance in the fingers and describe its "feel." What class of substances give this " feel " ? Put the rest of the sodium amalgam into a test tube, fill nearly full with strong ammonium chlorid solution, and when the ammonium amalgam begins to run out of the tube, fill it completely full with water, close with the thumb and invert over water. Try to keep as much of the ammonium amalgam as possible under the mouth of the test tube so that the gas which forms may be collected therein. When the test tube is full, test the gas. What is it? EXPERIMENT 126. Solvay Process of Sodium Car- bonate Manufacture. Prepare saturated solutions (about 100 <:) of ammonium carbonate and of sodium chlorid by shaking the finely powdered salts for some time with water. Decant the saturated solutions and pass washed carbon dioxid into the ammonium car- bonate until no more is absorbed. Now mix the two solutions, stir well, and run in carbon dioxid. If a pre- cipitate does not appear in a few minutes, shake well for some time, and run in carbon dioxid again. When a considerable amount of the precipitate has formed, prove it to contain carbon dioxid and sodium by appro- priate tests. EXPERIMENT 127. Flame Tests. Wash apiece of platinum wire as clean as possible and then hold it ir> a Bunsen flame until the latter is no longer tinged by vt. Dip its end in some sodium compound and bring into the flame ; note the color. Clean the wire again, dip into some potassium compound, and hold in the 92 Elementary Chemistry flame. Unless the potassium compound is entirely free from an admixture of sodium compounds, its character- istic color will be masked by that of sodium. When the flame is observed through cobalt blue glass, however, as the sodium flame color is absorbed, that of potassium alone is seen. If a lithium salt is available, familiarize yourself with its flame test also. EXPERIMENT 128. Preparation and Properties of the Nitrates of the Alkali Metals, (a) Put a little sodium hydroxid (or carbonate) into a dish, add a little water, and with constant stirring dilute nitric acid until a slightly acid reaction, (litmus paper) is obtained. Set the dish aside and examine it from day to day. (b) Go through similar operations with potassium hydroxid or carbonate instead of sodium. (c) When crystals have formed from both solutions, remove several specimens of each and compare their shape carefully. Write a careful description of each. Do you now see any reason for calling sodium nitrate cubical niter, as is sometimes done ? (d) Heat a few crystals of potassium nitrate in a test tube until they melt and effervesce. Now drop into the tube a piece (2 ) of charcoal. Describe what happens. Repeat with sulfur instead of charcoal. EXPERIMENT 129. Test for a Nitrate. Fill a small test tube about a fifth full of clear crystals of ferrous sulfate (green vitriol), and then about half full of water. Shake until a clear solution results. To this add a crystal of potassium nitrate about the size of a pin- head. Fill another test tube about a sixth full of concen- trated sulfuric acid and, holding both test tubes as nearly horizontal as possible, run the solution upon the sulfuric acid so that the two liquids mix as little as Experiments 93 possible. The brown ring shown where the solution floats upon the acid indicates the presence of a nitrate. Make a fresh solution of ferrous sulfate, and repeat the test without adding 1 potassium nitrate. Does the brown ring appear? EQUIVALENT WEIGHTS EXPERIMENT 130. (Quantitative^) Equivalent of Sodium. Weigh out to centigrams a piece of clean lead foil about 10 cm - square. Cut off a piece of sodium (about 4 mm - long and 2 mm - cross section), scrape off the coating of oxid and, after wiping it dry on filter paper, roll it into a cylindrical form. The weight of this cylinder should be about 0.9^-. Carefully roll the sodium up in the foil, leaving one end open, but pinch- ing the other end tightly together. By this arrange- ment the exposed surface of the sodium alone can be acted upon by water, and the evolution of hydrogen is quite steady. Weigh to centigrams the sodium and foil. The weight of the sodium is found by subtracting the weight of the foil from that of the foil and sodium. Fill a 500 c - c - graduated cylinder with water, close it with a piece of paper, and invert it in a pneumatic trough containing only a shallow depth of water. Drop the sodium wrapped in the foil in the water and at once place over it the inverted cylinder to catch all of the escaping hydrogen. When no more gas is given off, bring the water inside and outside the cylinder to the same level by raising the cylinder or by pouring water into the trough, and read off the volume. Also read the barometer and the thermometer. Reduce the vol- ume to standard conditions, correcting for aqueous ten- sion, and multiply the reduced volume by 0.09 (the weight of a liter of hydrogen) to find the weight of hydrogen evolved. The quotient obtained by dividing 94 Elementary Chemistry the weight of the sodium by that of the hydrogen is the equivalent of sodium. EXPB:RIMENT 131. (Quantitative^) Equivalent of Zinc. I. Weigh out to centigrams about 5 & of zinc (chemically pure, if possible), and put it into a gas gen- erator provided with a stopcock funnel. Connect the generator with an aspirating bottle (Fig. 24) of at least 2 l - capacity. Cover the zinc with a little \vater and close the stopcock. The delivery tube is placed in a vessel of water with the levels of the liquid in the ves- sel and in the aspirator the same when the delivery tube is open. Close the delivery tube and place it in a tared bottle or beaker holding at least 2 / -. Measure out with a pipette or a graduate 50^- of strong hydrochloric acid, put a portion of it in the stop- cock funnel, open the cock cautiously and let the acid run into the generator; be very careful to prevent any air being drawn into the generator. Add the acid from time to time so as to keep up a rapid evolution of the gas. When no more hydrogen is given off, add all of the acid, if it has not already all been added, arrange the aspirating and receiving bottle so that their water levels are the same and, opening the stopcock, let the acid drain into the generator. Let the apparatus stand for several minutes to come to the temperature of the room, and then close the delivery tube and lift it out of the receiving vessel. Weigh or measure the volume of the water expelled from the aspirator by the hydrogen, read the barometer and thermometer, and reduce the volume to standard conditions, allowing for aqueous tension. Multiply this reduced volume by 0.09 (the weight of a liter of hydrogen) to get the weight of the hydrogen evolved. Divide the weight of the zinc by the weight of the hydrogen ; the quotient is the equiv- alent of zinc desired. Experiments 95 EXPERIMENT 132. (Quantitative^ Equivalent of Magnesium. The apparatus and operations are like those in Experiment 131 : about 2?- of the metal should be taken. EXPERIMENT 133. (Quantitative.} Equivalent of Zinc. II. (Hood.) Clean, dry, and weigh to centi- grams an evaporating dish, together with a funnel, which, when inverted, fits securely into the dish. Put 3 to 4-?- of zinc (preferably chemically pure, although ordinary or mossy zinc will do) in the dish, replace the funnel and weigh to centigrams. Support the dish on a ring of a stand, and pour in beside the funnel a little strong nitric acid so that it can flow under the funnel and attack the zinc. As soon as the action subsides a little, add more acid, and continue in this way until all the acid is dissolved. Now evaporate to dryness, using a large flame. When the contents of the dish appear dry, gradually increase the heat, finally heating as hot as possible for at least five minutes. Let the dish cool and weigh it. Again heat to redness for several min- utes and weigh, continuing in this way until the dish and contents do not lose more than 3 c s- on heating. The substance remaining is zinc oxid ; the zinc nitrate at first formed is decomposed by the heating. How many grams of zinc oxid have you obtained? How much oxygen has combined with the zinc taken ? What is the ratio of the weights of the zinc and oxy- gen ? Taking the equivalent of oxygen as 8, what is the equivalent of zinc as deduced from this experi- ment? EXPERIMENT 134. (Quantitative^ To Determine the Vapor Density of Alcohol by Dumas' Method. Fit a clean, dry flask (100 to 250 c - c -) with a one-hole rubber stopper through which is thrust a bit of glass tubing with its upper end drawn out to a diameter of Elementary Chemistry about a millimeter (Fig. 61), and after rubbing the stopper with a little vaseline so as to make it fit gas-tight, weigh the apparatus to centigrams (or better, milligrams). Take the temperature and pressure of the air. Put about 20 c - c - of alcohol into the flask and immerse it up to its neck in boiling water contained in a beaker or can, hold- ing it submerged by means of a clamp. Take the temperature of the boiling water. When the alcohol has almost all boiled away bring a Bunsen flame to the tip of the glass tube, and as soon as the alcohol flame goes out (an in- dication that the flask contains only alcohol vapor) seal off. Weigh the flask again with the same degree of accuracy as before. Hold the neck of the flask under water and with tongs or pinchers break off the tip of the sealed tube. The flask should promptly fill almost completely with water; if it does not, the experiment must be repeated. Weigh the flask thus filled with water, to decigrams only, on a platform balance. The difference Fig. 6l DETERMINING THE VAPOR DENSITY OF ALCOHOL A short piece of rubber tubing, closed by a pinch- cock, is substituted for the glass tip Experiments 97 between the weights of the flask filled with water and with air gives the weight of the water, which, as one cubic centimeter of water weighs one gram, also gives the volume of the air and of the alcohol vapor. The calculation of the results are given on page 215 of the text. SULFUR AND ITS COMPOUNDS EXPERIMENT 135. Properties of Sulfur, (a) Re- view the observations you made on sulfur in Experi- ments i and 2. (b) Fill a test tube nearly half full of sulfur and, grasping it with a holder, heat it carefully. What is the color of the sulfur just after it melts ? Pour a drop or so into cold water and compare the product with the original sulfur taken. Heat the tube so as to raise the temperature of the melted sulfur gradually, and from time to time tilt the tube. What changes occur in its color and viscosity ? Do you find that at a certain tem- perature the sulfur becomes so viscid that you can invert the tube without the sulfur running out ? Heat to boiling. Pour the boiling sulfur slowly and in a thin stream into cold water contained in a dish or beaker, moving the tube around so that the sulfur may solidify in a long spiral rod. Examine the product, especially as to color, hardness, and elasticity. Put it away in the desk and examine it from time to time for a week or so. What changes take place ? (c) Fill a combustion cup with sulfur, set it on fire, and then put the cup in the bottom of a wide-mouthed bottle, covering it with a piece of cardboard. When the sulfur ceases to burn, introduce a piece of dry blue litmus paper. What change of color ? Then put in a piece of wet blue litmus paper and note result. (d) Review Experiment 7, I. 98 Elementary Chemistry NOTE. Experiment ij6 must be performed in the hood. EXPERIMENT 136. Preparation and Properties of Hydrogen Sulfid. Place a little ferrous sulfid in a test tube and add some dilute sulfuric acid. If a gas is not given off, heat gently. Attach a delivery tube and collect a small test tube full of the gas by down- ward displacement (Fig. 44). Ignite the gas and see if you can detect the odor of burning sulfur. Pass the gas for several minutes into about 2 C - C - of strong nitric acid in a test tube. When the inside of the end of the delivery tube becomes coated with a yellow substance, substitute a new delivery tube and put it into a second test tube filled with water. This will yield a solution of hydrogen sulfid. Rinse out the first delivery tube, pick out some of the deposit and by means of appropri- ate tests establish its identity. Add some of the hydrogen sulfid solution to a little dilute copper sulfate, CuSO 4 , solution. Result ? Repeat with lead acetate, Pb(C 2 H 3 O 2 ) 2 , solution; with cad- mium sulfate, CdSO 4 , solution ; with potassium perman- ganate (KMnO 4 ) solution, bromin water, and chlorin water. What is the result in each case ? If copper, lead, cadmium, and sulfur are all bivalent elements, what are the formulas of the products ? Write the equations for the reactions. Repeat these tests, delivering the hydrogen sulfid gas directly into the solutions of the salts. EXPERIMENT 137. Preparation of Sulfur Dioxid. (a) By the burning of sulfur. Review Experi- ment 2. (b) By the decomposition of sulfuric acid by copper. Put about 10^- of copper in a flask provided with a cork and delivery tube with interposed "safety bottle" (Fig. 55), and add about 40 c - c - of strong sulfuric acid. Heat the flask cautiously, removing the flame when the Experiments 99 effervescence may become too brisk, and collect two receivers full by downward displacement. Cover the bottles well and reserve for use in Experiment 138. Let the gas pass into a beaker half full of water for a few minutes, so as to prepare a solution of sulfur dioxid (sulfurous acid). (c) By t/ie action of dilute sulfuric acid on sodium sulfite. Put a layer of sodium sulfite nearly a centi- meter thick in the bottom of a gas generator, barely cover it with water, and add through the funnel tube from time to time dilute sulfuric acid so as to keep up a rapid evolution of gas. Collect t\vo receivers full by dow r nward displacement, cover them well and reserve for Experiment 138. Prepare a solution of sulfur dioxid by passing the gas into some water in a beaker or a bottle, and save for Experiment 139. EXPERIMENT 138. Properties of Sulfur Dioxid. Bleaching Action, Place in a receiver full of sulfur dioxid a piece of moistened calico, some petals of a red flower (carnation), cover and allow to stand for half an hour or so. What happens ? Remove the object intro- duced and place it in a dish containing very dilute sul- furic acid. What change in color ensues ? Oxidation by Nitric Acid. Pour a few drops of strong nitric acid into a receiver filled with sulfur dioxid, cover and move the receiver around so that its inside walls may become moistened with the acid. What visible evidence is there that the nitric acid is being reduced ? To prove that the sulfur dioxid has been changed into the trioxid (which dissolves in the water to form sulfuric acid), rinse out the receiver with a little water, pour into a test tube and add barium chlorid solution. The appearance of the white precipi- tate of barium sulfate indicates the presence of sulfuric acid. ioo Elementary Chemistry EXPERIMENT 139. Properties of Sulfurous Acid. Test the action of the solution of sulfur dioxicl prepared in Experiment 137 on litmus paper. Cautiously taste a drop of it on a stirring rod. Pour some of it into an evaporating dish, add a few drops of litmus solution or other indicator, neutralize with sodium hydroxid solu- tion and evaporate the solution to dryness. How can you prove that the white residue is the salt, sodium sulfite, Na 2 SO 3 ? Add a drop or so of potassium permanganate solu- tion to a little sulfurous acid in a test tube. Repeat, using potassium dichromate instead of permanganate. Compare results. EXPERIMENT 140. Properties of Sulfuric Acid. Decomposition by /teat : Place not more than one drop of strong sulfuric acid in a porcelain dish and heat. Heat generated on mixing with water : Pour a few drops of strong sulfuric acid into a test tube half filled with water. Action of organic substances: Try the action successively of a few drops of strong sulfuric acid on (a) a splinter of wood, (/;) a piece of paper, (c) a piece of colored cloth, (d) a little sugar, (c) a little starch. It may be necessary to heat gently in the last two cases. PHOSPHORUS CAUTION. All experiments with phosphorus should be carried out with the utmost caution, as the ready inflammability of the yellow modification of the element makes such experiments dangerous. The waxy modification should never be touched with the fingers and should be handled and cut UNDER WATER. At the conclusion of an experiment all bits of phosphorus left over should be carefully collected and burned. Experiments 101 EXPERIMENT 141. Physical Properties of Phos- phorus. Examine both red and yellow phosphorus, carefully noting their chief characteristics. Put a piece (3 mm.) of yellow phosphorus in a small dry test tube and add about 3 c - c - of carbon bisulfid. CAUTION. Be sure that no flames are near. Shake carefully for a minute or so. Pour the solu- tion, every bit of if, upon two or three pieces of filter paper laid on a ring of a retort stand and set the stand back out of the way. While waiting for the carbon bisulfid to evaporate, put a pinch of red phosphorus in a small dry test tube, add about 3 c - c - of carbon bisulfid, shake for a minute or so, filter through a dry filter paper, catch the filtrate in a watch glass, and allow to evaporate (in the hood). Is red phosphorus soluble in carbon bisulfid ? What hap- pens to the solution of yellow phosphorus poured on the filter paper? How do you account for the result? EXPERIMENT 142. Conversion of Red Phosphorus into Yellow Phosphorus. Put a pinch of red phos- phorus in the bottom of a small ignition tube 7 , hold the tube horizontally with the tongs, and gently heat the bottom of the tube. When nearly all the red phos- phorus has disappeared, let the tube cool, then make a scratch just below the deposit that has collected in the cooler part of the tube and break the tube. Rub the deposit with a glass rod or match stick. How do you know that yellow phosphorus has been formed ? Do not neglect to heat both parts of the tube to redness so as to burn up all the phosphorus. EXPERIMENT 143. Preparation and Properties of Phosphin. Fill a test tube fitted with a two-hole cork, through which pass tubes as shown in Fig. 62, about one-fourth full with sodium hydroxid solution, and put into it a piece (4 *) of phosphorus. Connect the tube 102 Elementary Chemistry which dips into the soda solution with the gas supply and pass through the apparatus ordinary illuminating gas until the air is expelled. How can you prove this to be the case? Shut off the gas and gently heat the contents of the test tube, keeping the end of the delivery tube below water in a dish. How do you account for the rings of smoke that appear ? EXPERIMENT 144. Preparation of Me- taphosphoric Acid. Put a little heap of red phosphorus on a piece of asbestos paper (or in a porce- lain crucible) set in a crockery plate, ignite the phosphorus and invert over it a perfectly dry wide-rnouthed bottle. When the phosphorus ceases to burn set the bottle upright. Pour a few drops of cold water on the phos- phorus pentoxid formed, noting any hissing noise, and test the solution with blue litmus. Put the solution into a test tube and add silver nitrate solution. What is the precipitate formed ? EXPERIMENT 145. Preparation of Orthophos- phoric Acid. Put a little (i cm - circle) red phosphorus in an evaporating dish, cover it with nitric acid, and heat gently. When the action has ceased, filter, if the solution is not clear, and evaporate the filtrate on the water bath. Redissolve the sirup which remains in a little water. What is its action on blue litmus paper? FlG. 62 CONVENIENT APPARATUS FOR PRE- PARING PHOSPHIN Experimen ts 103 Add silver nitrate solution and note nature of the pre- cipitate of silver orthophosphate, Ag 3 PO 4 . If the pre- cipitate is of a dark color, it is evident that some phos- phorus acid was formed also. In that case it is well to add silver nitrate solution to a solution of commercial orthophosphoric acid. EXPERIMENT 146. Reactions of Phosphates. To a solution of sodium hydrogen phosphate, Na 2 HPO 4 , add some calcium chlorid, CaCl 2 , solution. The pre- cipitate is secondary calcium phosphate, CaHPO 4 . Prepare some "magnesia mixture" by mixing a little ammonia hydroxid and ammonium chlorid with magne- sium sulfate, and add it to a solution of acid sodium phosphate. The precipitate is magnesium ammonium phosphate, (NH 4 )MgPO 4 . ARSENIC AND ANTIMONY EXPERIMENT 147. Properties of Arsenic. Note the physical properties of arsenic. In what respects does it resemble metals? Heat a small particle of the element on a porcelain crucible cover, noting particu- larly any odor. EXPERIMENT 148. Arsin. {Marsh's Test for Arsenic.) Generate hydrogen in a generator provided with a long ( 2 5 cm ') glass delivery tube drawn out to a jet. Use none but chemically pure materials. When the air is displaced, light the hydrogen at the tip. Heat the glass tube nearest the generator with a Bunsen flame. If a deposit appears in the cold part of the tube, the zinc or sulfuric acid is impure and the experiment should be discontinued and other materials used. If no subli- mate appears and the hydrogen burns with colorless or slightly yellow flame, and leaves no spot on the bottom of a porcelain dish pressed down upon it an instant, pour a few drops of an arsenical solution down the IO4 Elementary Chemistry funnel tube. Heat the tube and note the appearance of sublimate and the color of hydrogen flame. Press the porcelain dish in the flame a moment and add a couple of drops of sodium hypochlorite solution to the spot. Soak pieces of green paper in water and test the water for arsenic as above. EXPERIMENT 149. Arsenic Trioxid, Trichlorid, and Trisulfid. (a) Mix a pinch of arsenic trioxid with an equal bulk of powdered charcoal, put the mixture in an ignition tube, and slip down over it a loosely fitting plug of charcoal. With the tongs hold the tube in a flame so as to keep the charcoal plug red- hot while heating the mixture of charcoal and oxid. What is the nature of the deposit that forms in the cooler part of the tube ? How can you prove this deposit to be arsenic ? (b) Heat carefully a pinch of arsenic trioxid with sodium hydroxid solution. Sodium arsenite, Na 2 AsO 3 , is formed. (c) Boil a little of the trioxid with concentrated hydrochloric acid. Result ? Dilute with an equal vol- ume of water. Arsenic trichlorid is formed. (d) Pass hydrogen sulfid into the solution from (c). What is the color and appearance of the precipitate ? Let the precipitate settle, pour off the supernatant liquid, add some ammonium sulfid to the residue, warm gently, and shake well for some time. Soluble ammonium sulfo-arsenite, ( ) 2 AsS 3 , is formed. To a little of this solution add a slight excess of hydrochloric acid. What happens ? EXPERIMENT 150. Arsenic Acid. Boil a little arsenic with nitric acid for some time, then add just enough ammonium hydroxid to effect neutralization. To part of this solution add silver nitrate solution, and Experiments 105 to another, "magnesia mixture." Compare results with those obtained in Experiment 146. EXPERIMENT 151. Properties of Antimony. Note the physical properties of various samples of antimony that may be available. EXPERIMENT 152. Stibin. Follow the directions in Experiment 148, substituting antimony trichlorid (Experiment 153) for the arsenical solution. EXPERIMENT 153. Antimony Trioxid, Trichlorid, and Trisulfid. (a) Repeat Experiment 149 (a), substi- tuting antimony trioxid for arsenic trioxid, and com- pare results. (b) Boil a little powdered antimony with sodium hydroxid solution and compare results with those obtained in Experiment 149 (#). (c) Place some powdered antimony in a test tube and add about 3 c - c - of concentrated hydrochloric acid and one cubic centimeter of concentrated nitric acid. If a reaction does not start promptly, warm a little, and let it continue for at least ten minutes. Then dilute with five times its bulk of water and, if the solution is not clear, filter it. Pass hydrogen sulfid into the solu- tion of antimony trichlorid thus prepared. If a precip- itate does not soon form, add more water. Treat the precipitate of antimony trisulfid, Sb 2 S 3 , as directed in Experiment 149 (c) and (d). (d) Heat some powdered antimony with concen- trated nitric acid and compare results with those obtained in Experiment 150. BISMUTH EXPERIMENT 154. Properties of Bismuth. Note the physical properties of bismuth. Try to dissolve a bit of it in (i) concentrated hydrochloric and (2) con- centrated nitric acid. io6 Elementary Chemistry EXPERIMENT 155. Reactions of Salts of Bismuth. Place a few small crystals of bismuth nitrate in a test tube, fill the tube a quarter full with water, and add small amounts of concentrated hydrochloric acid until a clear solution is obtained. Pour a few drops of the solution into water, nearly filling- a test tube. The white precipitate is bismuth subnitrate, BiONO 3 . Pass hydrogen sulfid through the rest of the solution. Filter out the bismuth sulfid, Bi 2 S 3 , and treat with warm yel- low ammonium sulfid. Filter and acidify the filtrate with hydrochloric acid. Compare the result with Ex- periments 149 (d) and 153 (c). How can sulfid of bis- muth be separated from those of arsenic and antimony ? MAGNESIUM EXPERIMENT 156. Properties of Magnesium. Scrape a piece of magnesium wire or ribbon bright and note its most obvious physical properties. Grasp one end of a short piece with tongs and hold it in a Bunsen flame. What is the product and what are its properties ? Treat a little magnesium in a test tube with dilute hydrochloric or sulfuric acid. What gas is evolved? EXPERIMENT 157. Reactions of Magnesium Salts. To a little magnesium sulfate solution add sodium or ammonium carbonate solution. Also add sodium or ammonium carbonate solution to magnesium chlorid solution. Compare results. What are the products? To about 5 c - c - of magnesium sulfate solution add about one cubic centimeter each of ammonium hydroxid and ammonium chlorid solution. Then add disodium hydrogen phosphate solution. The precipitate is mag- nesium ammonium phosphate (NH 4 )MgPO 4 . EXPERIMENT 158. Preparation of Magnesium Sulfate. Place about 20 #- of magnesite in a beaker or flask and add 30 to 40 c - c - of dilute sulfuric acid. If Experiments 107 effervescence is not vigorous, heat a little. When solu- tion is complete, filter and evaporate the filtrate to crystallization on a water bath. Pour off the mother liquor from the crystals and dry them by pressing between folds of filter paper. EXPERIMENT 159. Preparation and Properties of Calcium Oxid (Lime) and Hydroxid (Slaked Lime). Test a piece of marble (12 mm -) with wet red litmus paper. What reaction does it show ? Support the lump on a frame of iron wire laid across a ring of a stand, and heat as hot as possible, using two Bunsen flames, or, better, a blast lamp. After heating for about fifteen minutes remove the flames, and as soon as the lump is cold, test it again with wet red litmus paper. What change has supervened ? Place the lump of quicklime in a dish or saucer and pour water upon it drop by drop as long as it is taken up readily. Do not .add too much water. Keep the lump under observation for some time, and note any changes (heat, volume, appearance). Put some of this slaked lime in a bottle and fill the bottle with distilled water. Shake up well, let settle, and decant the clear liquid into another bottle, and label it "Lime Water." EXPERIMENT 160. Some Properties of Several Calcium Compounds. Review Experiment 67. Place a piece of old mortar in a test tube, add dilute hydro- chloric acid, and identify the gas. Stir up some (5 cm - circle) plaster of Paris with enough water to make a thick paste. Spread the paste on a piece of paper and lay on it a coin covered with a thin coating of vaseline, embedding it slightly in the paste. (Do not delay to wash out the dish, as the plaster of Paris is hard to remove after it has set.) Carefully remove the coin after the plaster has set for io8 Elementary Chemistry an hour or more. To about 2 c - c - of a solution of calcium salt (chloric! or nitrate) add ammonium or sodium car- bonate solution. Repeat, using ammonium oxalate solution instead of a carbonate solution. Try the flame test (Experiment 127) with (i) cal- cium chlorid and (2) calcium sulfate. Review Experiment 38 for water of crystallization of gypsum. EXPERIMENT 161. Reactions of Strontium and Barium Salts, (a) To a little strontium chlorid solu- tion in a test tube add a few drops of ammonium car- bonate solution. Also ascertain the reaction between a solution of strontium chlorid and dilute sulfuric acid. (I?) Test solutions of barium chlorid with ammonium carbonate and dilute sulfuric acid. Try the flame tests, using (i) strontium chlorid, (2) strontium nitrate, (3) barium chlorid, and (4) barium nitrate. Look at the flames through a spectroscope or through a diffraction grating, if these instruments are at hand. BORON AND SILICON EXPERIMENT 162. Preparation of Boric Acid. Put about 2$#- (7 cm - circle) of borax in a beaker and add about ioo c - c - of water. Heat and stir until the borax is all dissolved ; filter if the solution is not clear. To the hot solution add enough strong hydrochloric acid to make it decidedly acid to litmus paper. Allow the solution to cool and stand for some time. Then filter off the boric acid crystals which have formed, and purify them by recrystallization from the smallest pos- sible amount of boiling water. EXPERIMENT 163. Characteristic Reaction of Boron Compounds. Dissolve a pinch of boric acid in about 2 c - c - of strong alcohol contained in an evapo- rating dish. Dip a tuft of asbestos into the solution Experiments 109 and, holding it with tongs, set the alcohol on fire. What is the color of the name ? Ignite the rest of the solu- tion in the dish. EXPERIMENT 164. Borax Bead. Make a small (less than a millimeter in diameter) loop at the end of a piece of platinum wire by winding it around the point of a lead pencil. Heat it and touch it to a small lump (2 **) of borax. Then heat the borax until a clear, glass-like bead is obtained in the loop. Bring the hot bead in con- tact with a minute particle of some cobalt or iron com- pound and heat in the flame. What color is imparted to the bead ? EXPERIMENT 165. Preparation of Magnesium Sil- icid and of Silicon Hydrid. Mix well on a piece of paper equal parts (2 cm - circle) of powdered magnesium and very fine sand, place the mixture in a small test tube and, grasping it with a test tube holder or paper and tongs, with its mouth pointing so that any of the substance which may be projected from the tube can do no harm, hold it steadily in the tip of a Bunsen flame. After the completion of the reaction break the test tube and throw small portions of the product (mag- nesium silicid) into dilute hydrochloric acid contained in an evaporating dish or beaker. What takes place ? What compound of silicon is spontaneously inflammable ? EXPERIMENT 166. Preparation of Silicic Acids. To about 5 c - c - of a concentrated solution of " water glass " (a crude mixture of sodium and potassium sili- cates) add in small proportions hydrochloric acid until the mixture is strongly acid to litmus paper. Put a little of the thick, gelatinous mass (a mixture of ortho- silicic and metasilicic acids) on a piece of platinum foil, evaporate to dryness, and heat strongly. Add a drop of water to the white residue, and test it with litmus paper. What is the powder ? no Elementary Chemistry ZINC EXPERIMENT 167. Properties of Zinc. Ascertain the most obvious characteristics of as many different forms (mossy, granulated, powdered, stick) of zinc as possible. Review Experiments 18 and 104. In Experi- ment 1 8 hydrogen and zinc chlorid were formed ; in Experiment 104 hydrogen and sodium zincate. EXPERIMENT 168. Reactions of Zinc Salts, (a) Fill a test tube about a fourth full of zinc sulfate or chlorid solution and add a drop or two of sodium hydroxid solution. What is the precipitate formed ? Now add little by little enough sodium hydroxid solu- tion to redissolve the precipitate formed at first. The alkalin solution contains sodium zincate. (b) Fill a test tube about a third full of zinc sulfate solution and add a drop of dilute hydrochloric acid. What is the reaction of the mixture (litmus) ? Pass in hydrogen sulfid for a few minutes. Result ? No\v transfer the mixture to a beaker and add half its vol- ume of ammonium sulfid. The precipitate is zinc sul- fid. Test with litmus. What must the reaction of a zinc salt solution be in order that the sulfid may be precipitated ? EXPERIMENT 169. Blowpipe Reactions. Heat a small piece of zinc on charcoal in the oxidizing flame of a blowpipe. Moisten the incrustation with a drop of cobalt nitrate solution and heat again in the oxid- izing flame. Result? CADMIUM EXPERIMENT 170. Properties and Reactions. Examine a piece of the cadmium, and note its most obvious properties. Into a dilute solution of cadmium chlorid or sulfate pass hydrogen sulfid gas. The precipitate which forms Experiments 1 1 1 is cadmium sulfid, CdS. Make the solution acid by adding a few drops of hydrochloric acid. Is cadmium sulfid soluble in dilute hydrochloric acid ? Wash the precipitate by decantation and add ammo- nium sulfid solution. Is the precipitate redissolved? How can cadmium sulfid be distinguished from other yellow sulfids? Add sodium hydroxid solution in excess to a solution of a cadmium salt. Is the hydroxid precipitated solu- ble in caustic alkali solution? MERCURY EXPERIMENT 171. Preparation of Mercury. Put a little cinnabar near one end of a glass tube (15"*- long) open at both ends, and heat the glass under the cinnabar strongly, holding the tube in a slanting posi- tion and rotating it constantly. What gaseous products are formed? What is deposited in the cooler part of the tube ? Mix a pinch of mercury chlorid with two or three times its bulk of dry powdered sodium carbonate, and heat the mixture in an ignition tube. Note the nature of the sublimate. EXPERIMENT 172. Mercurous Nitrate. Fill the rounded end of a test tube nearly full of mercury, add about 5 c - c - of water, and then about $ c - c - of concentrated nitric acid. Let the action go on for an hour or so. In the meantime perform Experiment 173. Pour the contents of the tube off from any mercury that is left into a small beaker, dissolve in the least possible amount of water any crystals which may have formed, rinse out the tube with about 2O C - C - of water, put the rinse water into the beaker, and add one or two drops of concen- trated nitric acid, so as to have a clear solution. Save the solution for Experiment 174. H2 Elementary Chemistry EXPERIMENT 173. Mercuric Nitrate. Dissolve about half as much mercury as was used in Experiment 172 in about io c - c - of concentrated nitric acid. Dilute the solution of mercuric nitrate thus formed with an equal volume of water. EXPERIMENT 174. Reactions of Mercurous Salts. To 2 c - c - of mercurous nitrate solution add hydrogen sulfid. The precipitate is a mixture of mercuric sulfid and mercury. Add to separate portions of the solu- tion, hydrochloric acid and potassium iodid solution, respectively. Add ammonium hydroxid to the precipi- tate from hydrochloric acid. What are the precipitates ? Put a strip of zinc and of copper (or copper wire) into portions of the mercurous nitrate solution. In a few minutes remove them and rub them dry. What has happened ? Rub a cent or a dime with a piece of paper' wet with mercurous nitrate solution. EXPERIMENT 175. Reactions of Mercuric Salts. Pass hydrogen sulfid into the mercuric nitrate solution. The precipitate is mercuric sulfid, HgS. Add to sepa- rate portions of mercuric nitrate solution, hydrochloric acid and potassium io^id solution (this drop by drop). What are the precipitates ? ALUMINUM EXPERIMENT 1 76. Properties of Aluminum. Exam- ine as many different forms of aluminum as are avail- able, also of its alloys ; note their most prominent physical features. EXPERIMENT 177. Action of Acids and Alkalis on Aluminum. Fill the rounded end of a test tube with aluminum, add about twice its volume of concentrated hydrochloric acid, and warm and test the gas evolved. Repeat, using sodium hydroxid solution (cf. Experi- ment 27). The solution contains sodium aluminate. Experiments 113 EXPERIMENT 178. Action of Mordants. Soak a piece of white cotton cloth in a strong solution of cochi- neal or indigo for a minute or so ; then wring it out and dry it. Try to wash out the color, using soap. Dip a similar piece of cloth in a solution of aluminum acetate and dry it. Then soak it in the cochineal or indigo solution and dry it. Try to wash out its color. EXPERIMENT 179. Alums. Weigh out to a decigram quantities of aluminum sulfate, A1 2 (SO 4 ) 3 -(- i8H 2 O, and potassium sulfate, K 2 SO 4 , in the ratio of their molecular weights, i. e. 770 : 137. Fifteen grams of the first salt to 3 grams of the last are good working quan- tities. Dissolve each in the smallest possible quantity of boiling water in a test tube. Mix the two solutions hot in an evaporating dish and set aside to cool and crys- tallize. Note taste and form of crystals, Mix equal volumes of solutions of aluminum sul- fate and ammonium sulfate saturated at the boiling temperature. Set aside to crystallize. The product is ammonium alum. NOTE. Large crystals may be obtained by hanging a thread or string in the solution. EXPERIMENT 180. Reactions of Aluminum Com- pounds. Add a dilute solution of sodium carbonate to a dilute solution of alum. Filter the precipitate and wash it thoroughly. Transfer to a test tube, cover it with water, and add -hydrochloric acid. If the precipi- tate is a carbonate, there will be effervescence. Add ammonium sulfid solution to a solution of alum. Filter and wash the precipitate and, placing it in a test tube, add hydrochloric acid. If the precipitate is a sulfid, hydrogen sulfid gas will be evolved. To some aluminum sulfate solution in a test tube add about one-fifth as much sodium hydroxid. Transfer 114 Elementary Chemistry about half of the precipitate of aluminum hydroxid, A1(OH) 3 , thus formed to another test tube, and add an excess of sodium hydroxid. Sodium aluminate is formed. Is it soluble ? To the other half of the pre- cipitate add dilute hydrochloric acid. Compare results with those obtained for zinc in Experiment 168. TIN EXPERIMENT 181. Physical Properties. Examine a stick of tin and a piece of tin foil, and note the physical properties of the metal. Bend a stick of tin when held close to the ear. What information does your sense of hearing give you in regard to tin ? EXPERIMENT 182. Crystallization of Tin. Hold- ing a piece of tinplate by means of tongs, heat it in a flame until the tin coating commences to melt. Then immediately plunge it into cold water. Rub it over with a piece of filter paper wet with dilute aqua regia, then with paper wet with a solution of a caustic alkali. Note the crystalline figures brought out by the action of the solvents. EXPERIMENT 183. Action of Acids on Tin. Fill the rounded end of a test tube with granulated tin, and add enough concentrated hydrochloric acid to fill the test tube about a sixth full. Heat gently (in the hood) until effervescence commences and regulate the heat- ing so as to cause the hydrogen to be given off rapidly. When the action is about at an end, fill the test tube full of water, and save the solution of stannous chlorid thus formed for Experiments 184, 185, and 186. Put a small piece of tin in a test tube and add a little concen- trated nitric acid. As soon as the reaction begins set the tube in a bottle in the hood. The white product is metastannic acid. Heat a little tin with strong sulfuric acid in a test tube. Result ? Experiments 1 1 5 EXPERIMENT 184. Preparation of a Solution of Stannic Chlorid. Fill a small test tube about a sixth full of the stannous chlorid solution prepared in Experi- ment 183, and add a little aqua regia, or add bromin in small portions until its color ceases to be discharged, and boil to expel the excess of acid or bromin. What is the action of the aqua regia or the bromin ? Preserve the solution for use in Experiment 185. EXPERIMENT 185. Distinction Between Stannous and Stannic Salts, (a] To a little of the stannous chlorid solution prepared in Experiment 183 add a few drops of mercuric chlorid solution. Note the white precipitate of mercurous chlorid, HgCl. Add more of the mercuric solution and heat gently. The gray tinge imparted to the precipitate is due to mercury resulting from the reduction of the mercurous chlorid. (b) Add a few drops of mercuric chlorid solution to some of the stannic chlorid solution prepared in Experiment 184. What is the result? (c) Saturate with hydrogen sulfid (i) a little of the stannous chlorid solution, and (2) of the stannic chlorid solution, and compare results. (it) Neutralize the contents of each of the test tubes with ammonium hydroxid and add yellow ammo- nium sulfid. Shake up the mixtures in each case and compare results. Take fresh portions of the solutions of stannous and stannic chlorid, and add to each sodium hydroxid solution, a drop or two at a time. EXPERIMENT 186. Replacement of Tin by Zinc. Fill a test tube about one-fourth full of the stannous chlorid solution prepared in Experiment 183, and fill up with water. Put a narrow strip of sheet zinc in this diluted solution and examine after a little while. What is the appearance of the zinc ? 9 1 1 6 Elementary Chemistry EXPERIMENT 187. (Quantitative.'] (Hood.) To Determine the Equivalent of Tin. Weigh about 5.00^- of tin foil in an evaporating dish. Put most of it on a piece of paper and moisten what is left in the dish with strong nitric acid. When the action slackens, put a little more foil into the dish and then a little more acid. Use as little acid as possible, but be sure that all the tin is attacked and that there is no loss of metal from spattering. Cautiously evaporate to dryness with free flame, and finally heat as hot as possible for at least ten minutes. Weigh when it is cool, and after moistening with the acid heat again ; continue in this way until the weight remains practically unchanged. The product is a compound of oxygen. Taking the equivalent of oxygen as 7.94, calculate that of tin. If tin is quadrivalent in this compound, what is its atomic weight ? The specific heat of tin is 0.056 ; what is its atomic weight as deduced by Dulong and Petit's Rule ? LEAD EXPERIMENT 188. Physical Properties of Lead. Examine as many different samples of lead as possible. Cut a piece of lead with a knife and note appearance of freshly cut surface. EXPERIMENT 189. Deposition of Lead by Zinc. Fill a test tube nearly full of a solution of lead acetate (about 10 per cent) and put in it a narrow strip of sheet zinc. Examine after an hour or so. Pour off a little of the solution and test it for zinc. To remove the lead that may still be present add dilute sulfuric acid to the solution. As lead sulfate is not wholly insoluble in water, add an equal bulk of alcohol, in which the sulfate is quite insoluble. Filter off the lead sulfate, neutralize the filtrate with ammo- nium hydroxid, and add ammonium sulfid ; a white pre- cipitate of zinc sulfid results. In case all the lead has Experiments 117 not been removed from solution by sulfuric acid, the precipitate caused by ammonium sulfid will not be white, but more or less of a blackish color, depending tipon the amount of lead sulfid also precipitated. Hy- drogen sulfid is a better precipitant of lead than sulfuric acid, and it is possible to remove all the lead by its use. Acidify the solution with hydrochloric acid, pass hydro- gen sulfid through it, filter, and add ammonium hydroxid and then ammonium sulfid. EXPERIMENT 190. Action of Acids on Lead. Scrape three small pieces of lead bright and clean, place them in test tubes and cover with (i) nitric, (2) hydrochloric, and (3) sulfuric acid. If no action takes place promptly, heat to boiling. Note the nature of any gaseous products and change in the appearance of the lead. If the lead dissolves in any of the acids, let the action continue to completion, pour out the solution into an evaporating dish, and set aside to crystallize. EXPERIMENT 191. Preparation and Properties of Lead Monoxid. Heat on charcoal in the oxidizing flame of a blowpipe a very small bit of lead, and note any vapors and incrustation formed on the charcoal. Examine some litharge as to its physical properties and test its solubility in nitric, acetic, sulfuric, and hydro- chloric acids, both cold and hot. EXPERIMENT 192. Preparation and Properties of Red Lead. Mix about 2&- (2 cm - circle) of lead mon- oxid with about 0.5^- (2 cm - circle) of powdered potas- sium chlorate or nitrate, and heat the mixture in an iron spoon or dish. Note the physical properties of the product and compare it with other samples of red lead. Ascertain in what common acids red lead is soluble. EXPERIMENT 193. Preparation and Properties of Lead Dioxid. Place about 2 s- (2 cm - circle) of red lead in a test tube, add some dilute nitric acid, and heat to iiS Elementary Chemistry boiling for several minutes. Filter and wash the brown residue. Put a little of it in a test tube, add concen- trated hydrochloric acid, and heat gently. What gas is evolved ? What other peroxid behaves with hydro- chloric acid in a similar manner? EXPERIMENT 194. Reactions of Lead Salts. Put a little dilute solution of lead nitrate or acetate in six separate test tubes and add to one of each the follow- ing reagents, noting the nature of the precipitates : (1) Hydrogen sulfid. (2) Hydrochloric acid. Add several times as much water and heat to boiling. What change ? Cool by holding test tube in running^ water. What is the nature of the product ? (3) Sulfuric acid. (4) Potassium iodid solution. (5) Potassium dichromate solution. (6) Sodium hydroxid solution gradually and in small portions until in excess. EXPERIMENT 195. Action of Water on Lead. Fill a flask half full of water and bubble the breath through it for some time so as to charge the water with carbon dioxid. Scrape a piece of lead bright and clean, put it in the flask, cork, and let stand for a day or so. Then test portions of the water for lead by Experiment 189. If no lead is found to be present, let the lead act on the water for a day or so longer, or evaporate off most of the water and test again. Bear in mind that the lead which has dissolved may be so slight that the precipitate of lead sulfid may be so minute as merely to tinge the liquid brown. COPPER EXPERIMENT 196. Properties of Copper. Examine as many different forms of copper as are procurable ; note their most prominent characteristics. File a piece Experiments 119 of copper wire bright and heat it red hot. What is the black coating? Compare with Experiments 22 and no. EXPERIMENT 197. Precipitate of Copper. Hang a strip of zinc (scraped clean) in a neutral solution of copper sulfate ; also in another test tube containing copper sulfate solution suspend an iron nail filed bright. What soon occurs ? EXPERIMENT 198. Preparation and Properties of Cuprous Oxid. Dissolve 2 & of copper sulfate in 30 c - c - of water and add 10^- of Rochelle salt (sodium potas- sium tartrate) previously dissolved in 20 c - c - of water. Warm and filter. To the filtrate add IQC.C. o f a dilute solution of grape sugar, and then enough sodium hydroxid solution to dissolve any precipitate, and as much again, so as to make the solution strongly alka- lin. Boil gently until a decided change occurs. Filter off the cuprous oxid, Cu 2 O, formed, dry it, and compare with cupric oxid, CuO. EXPERIMENT 199. Reactions of Copper Salts. To a little copper sulfate add ammonium hydroxid in excess. Then repeat with sodium hydroxid instead of ammo- nium hydroxid. Heat a solution of copper sulfate to boiling and add sodium hydroxid. This precipitate is cupric oxid, CuO. Review Experiment 136 for the action of hydrogen sulfid on solutions of copper salts. Review Experiment 37 for water of crystallization in copper sulfate crystals. Dip a copper or platinum wire into copper sulfate solution, then take it out and heat it in a Bunsen flame; note the color imparted. EXPERIMENT 200. (Quantitative.) To Find the Equivalent of Copper. Clean some copper foil or wire with emery paper so that it is bright, and weigh to centigrams 3^- of it. Place the weighed copper in a I2O Elementary Chemistry small flask, barely cover it with water, and add concen- trated nitric acid in small portions, allowing plenty of time for the action to cease before adding a fresh por- tion. When solution is complete, transfer the liquid to a weighed evaporating dish, being careful not to lose any, and rinse out the flask two or three times with ^c.c. O f W ater, adding the rinsings to the dish. Cautiously evaporate to dryncss. The blue com- pound is copper nitrate, Cu(NO 3 ) 2 , which, when heated to a high temperature, decomposes into nitric oxid, oxy- gen, and copper oxid, CuO. Heat for at least ten min- utes as hot as possible even after the decomposition has seemed complete and then weigh the copper oxid. Heat again and so on to constant weight. The equivalent of oxygen is 7.94; find that of copper. Copper is bivalent in this compound. What then is its atomic weight ? SILVER EXPERIMENT 201. Preparation and Properties of Silver. I. Fill an evaporating dish a third full of sil- ver nitrate solution, and introduce a few globules of mercury. Set the dish aside in a safe place for a couple of days. The silver will then be found forming little crystals, usually attached to the mercury. Remove them with steel forceps and, after washing them well, put them in a bottle labeled " Silver." II. Pour concentrated nitric acid over a ten-cent piece in an evaporating dish or beaker, and when the action slackens, add more acid. Toward the last, heat may be applied. Add three or four times its volume of water and then hydrochloric acid until all the silver is removed as silver chlorid, AgCl. Let this precipitate settle and wash by clecantation several times. Then filter and wash free from an acid reaction. Divide it into two equal parts with a knife or spatula. Experiments \ 2 1 Place one part in a dish, cover with dilute sulfuric acid, and add a piece of zinc. The silver which collects as a gray powder is to be separated from the zinc, washed and dried. It is then to be placed in a hollow excavation in a piece of charcoal and heated with a blowpipe until it fuses into a globule. Place the second part in a cavity in a piece of char- coal, cover it with sodium carbonate, and reduce it with a blowpipe flame. Scrape the minute globules together and fuse them together into a single bead. EXPERIMENT 202. Reactions of Silver Salts, (a) Add a soluble chlorid solution, such as HC1 or NaCl, to a solution of silver nitrate. Boil, filter, and expose the silver chlorid to sunlight. Result ? (b) Add a potassium bromid solution to a solution of silver nitrate. Heat to boiling, filter, and separate the precipitate into two parts. To one add sodium thiosulfate solution, Na 2 S 2 O 3 . Result? Expose the other half to light. Result ? (c) Add potassium iodid solution to silver nitrate solution. Compare the properties of the precipitate with those of silver chlorid and bromid obtained in (a) and (b). IRON EXPERIMENT 203. Properties of Iron. Examine as many different forms as possible of the varieties of iron, note their most obvious physical properties, and try the action of a magnet on each. Which becomes permanently magnetized ? Introduce a pinch of iron powder into a Bunsen flame. What happens ? Review Experiments 7, I. (;/*); 25, 27, 28, and 51. To get "clean" ferrous reactions the ferrous solution must not be given a chance to oxidize. If the hydro- chloric acid solution be poured directly from the test tube while hydrogen is still being evolved, there is no 122 Elementary Chemistry danger of any ferric chlorid being present. Solutions of ferrous sulfate prepared from the crystals nearly always oxidize a little so that the true ferrous reaction is obscured by the ferric reaction. EXPERIMENT 204. Reactions of Ferrous Salts. Fill a test tube about a fifth full of iron (filings or small brads), add enough dilute hydrochloric acid to fill the test tube nearly half full, and warm, if necessary, to start the reaction. By appropriate tests identify the gas given off. Ferrous chlorid is formed in solution. (a) As soon as the action has almost ceased, pour a little of the solution into some sodium or ammonium hydroxid solution. Note the changes of color in the precipitate of ferrous hydroxid produced. To what are they due ? (l>) Add a little of the ferrous chlorid solution to a solution of potassium ferricyanid, and note nature of the precipitate of ferrous ferricyanid (Turnbull's blue). (OME OF THE ELEMENTS Atomic Weights Valence Melting Point Boiling Point Specific Gravity l H = i O - ib Approxi mate 26 9 19-3 1Q.6 27.1 120.2 TO. 9 27 120 4O III. Ill, V 700 (?) 440 -) 1300 (?) 2.67 6. 7 2 J ' V 74-4 .9 y v 75-o T- W 75 III, V 446-457 Red heat 5-69 36.4 137-4 137 II Above that of cast iron ) 3-75 06.9 208.5 208 III, V 268 1700 9.9 10.9 II. ii III In electric furnace p 2.6 79-36 79.96 80 I 7-3 63 3.1 (liq.) ii. 6 112.4 112 II 320 770 8.72 39-8 40.1 40 II Red heat p i. 6-1. 8 ( Diamond 3.5 11.91 12.00 12 IV p ? \ Graphite 2.2 \ Charcoal 1.5 35-18 35-45 35-5 I IO2 34 1-33 (liq-) 5i-7 52.1 5 2 II, III p p 6-7 58.56 59-o 59 II 1800 p 8.6 63.1 63.6 63-5 I, II IO5O ? 8.9 18.9 19. ig I ? 95 7 197.2 197 III 1030 p 19-3 l.OOO 1.008 I I 252. 5 i 25.90 126.85 127 I 114 1 20 4-95 55-5 55-9 56 II, III I TOO p 7.88 05-35 206.9 207 II, IV 325 p n-37 6.98 7-03 7 I 1 80 p o-59 24.18 24.36 24 II 750 1 100 i-75 54.6 55-o 55 TI 7-2 98.5 200 200 j I -38:9 357 13-59 58-3 58-7 58.5 ,i 1600 p 8.9 13-93 14.04 H III, V 2O3 194 13-93 15.88 16.00 16 II 1825 15.88 30.77 31.0 3i III, V 44.2 287] Yellow 1.83 Red 2.21 93 3 194-8 195 IV 2000 p 21-5 38.86 39-15 39 I 62.1 667 4.9 28.2 28 4 28 IV Above cast iron p 2-5 07. 12 107 93 108 I IOOO p 10.5 22.88 23-05 23 I 97-6 742 0-97 86.94 87.6 87 II Red heat p 2-5 31.83 32.06 32 IIJV.VI II4-5 448 2.0 18.1 119.0 119 II, IV 227 1600 7-3 64.9 65-4 65 II 420 930 7-i i Referred to water if the element be in a solid or a liquid state ; to tydrogen if in a gaseous state. [ xxvii ] xxviii Elementary Chemistry TABLE II TENSION OF WATER VAPOR 15 12 -itnm. 21 20 gfnm. 16 I7.K mm. 2_1 C 222 7#W. 17 14 4//tt. 25 27 >mm. 18 15 ^mm. 26 2Z omm. 10 1 6 3/w. 27 26 t; /#/. 20 . ij.^mm. 28 28 I w. 21 1 8 ^tnm. 2Q 29 Sim. ig -jmm. 30 v i.e. mm. TABLE III SOLUTIONS TO BE PREPARED The figures in parentheses indicate the number of cubic centi- meters (if the substance is a liquid) and the number of grams (if the substance is a solid) that are to be dissolved in water ; the solution should then be diluted to one liter. Acetic acid, (140) of 80$ acid. Alum (any one), (100). Aluminum chlorid, (TOO). Aluminum sulfate, (25). Ammonium carbonate. Dis- solve 2oo> and 22. It is to be noted that no one of the three numbers given has more than three figures ; hence, there are only three significant figures. Substituting in the for- mula ( 27), we have Below are given two calculations of the value of V, the one to the right retaining all figures after each mul- tiplication, the one to the left retaining in each product only three (significant) figures. 283 283 273 273 849 1981 566 77259 77259 3b xxxiv Elementary Chemistry 773 77259 662 662 4638 463554 4638 463554 5^726 5H45458 2 95 295 760 760 17700 17700 2065 2065 224200 224200 224) 512(228.5 224200) 51145458 (228.1 448 " _ 640 6305 448 4484 1920 18214 I79 2 17936 1280 2785 As is seen, the reduced volumes differ only in the first decimal place. But as the units are doubtful, the tenths are not significant. As the tenths in 228.5 i g -5> the number according to custom is increased to 229. It is thus manifest that the abbreviated operations give as good results as the detailed one. FORMS OF RECORD OF DATA It always saves time and energy to enter data as soon as obtained in some approved tabular form. Always use a note book, never a scrap of paper. Preserve all the arithmetical work so that, if necessary, it may be checked up with a second determination. Some forms of tabular entries are given at the end of the directions Forms of Record of Data xxxv for the performance of various experiments. A very common operation in quantitative work is the fol- lowing : A dish or other vessel is weighed, some substance placed in it, and a second weighing made. The differ- ence in the weights gives the weight of the substance. A good form of record for this operation is this : Wt. of dish, crucible, or test tube + substance = 47. 63^"- Wt. " _.. _ = 23.42^"- Wt. of substance = 24. 21^"- Suppose a substance is being heated to constant weight in an evaporating dish. A convenient form of record is the following : Wt. of dish + substance after heating for 20 min = 47.84^- Wt. " + " " 10 " more = 47.67^- Wt. + " 10 " " = 47.63