»»w» i^flvj) ^^ff (TOi »l>im H W W II» M IW W >III HI I IHHU MOWBWUMWUH< B¥ Aflt ft » £11. Class TXxm. Q Copyright N^. COPYRIGHT DEPOSIT. LABORATORY NOTES IN HOUSEHOLD CHEMISTRY FOR THE USE OF Students in Domestic Science BY H. T. VULTE, Ph. D., F. C. S., Adjunct Professor of Domestic Science in Teachers College, Columbia University, AND G. A. GOODELL, A.B., A.M., Instructor in Chemistry, Wellesley College. Easton, Pa. : The Chemical Publishing Company, 1904, I OCT 28 1904 ' eoPY 3 J \-' PREFACE. The following pages are written as a guide and intro- duction to the study of household science. It is not the object of the authors to put forth a work on the analysis of food and other kindred subjects met with in the practice of domestic science ; their sole aim is to throw some light upon the composition of food and other materials to the end that those practicing this most use- ful of arts may achieve better results by understanding the more important properties of materials with which they deal. Some knowledge of chemistry, both general and organic, is necessary and a clear idea of the essentials of physics is indispensable. It is hoped that teachers using the manual will com- municate with the authors in regard to any suggestions or improvements. The book is a pioneer in the subject and may be criticized on account of the selection of subjects; they are, however, those which have in the course of three years proved most useful to the authors' classes. The common and metric systems of weights and measures are used in the manual; in all exact experi- ments the metric system has been given the preference, but in cases where the experiment has a direct bearing on domestic science the common household units have been brought into play. CONSTRUCTION OF THE BUNSEN BURNER. Unscrew the tube, examine and light the inner jet. Examine the outer tube and collar that controls the air- ports. Turn off the gas and replace the tube. Now turn on the gas again, strike a match and approach it to the top of the tube. Always observe this latter pre- caution when lighting the Bunsen burner. Observe the character and color of the flame, move the collar on the tube and note the effect. Hold a piece of glass tubing near the top of the flame, remove from the flame and bend. Hold it in the same position in the yellow flame, and after removal observe the condition of the tube and try to bend it. Is there any apparent difference in the intensity of the heat developed ? lyOwer a piece of fine iron wire gauze half way in the flame, why does the flame fail to penetrate the gauze ? Apply a light above the gauze, explain the phenomena. Place a piece of paper on the gauze, lower it half way in the flame, notice the charred ring. Hold a splinter at the same point in the flame, note where it is charred and explain. Intro- duce the large end of a dropping tube into the flame near the tube, and approach a light near the exit. From the results of the last three experiments what is your idea of the combustion zone ? Carefully turn the gas down at the key, watch the effect, why does the flame disappear ? Now immediately turn the gas on full force and note the result. Approach a light to the upper end of the tube, observe the character of the flame, compare with the original flam^ MANIPULATING GI.ASS TUBING. 5 as to color and heating effect. Strike the rubber tube a quick blow with the closed hand and explain the result- ing phenomenon. Make a simple drawing illustrating the structure of the Bunsen burner, with the gas and air supply and the zones of combustion of the flame. INSTRUCTION FOR HANIPULATING GLASS TUBING AND CONSTRUCTING SIHRLE APPARATUS. Two kinds of glass, " hard " and " soft," are used in making apparatus for the laboratory. Hard glass is very brittle and quite infusible in the ordinary Bunsen flame. It is used in heavy apparatus where a high temperature is required for heating dry, but never liquid, substances, as the latter would cause it to break. It can usually be recognized by the striations on its surface and by its greenish-yellow color, best seen at the end of a broken tube. Soft glass is less brittle than the other variety, is easily fusible in the Bunsen flame and is used in the con- struction of thin apparatus (such as beakers, test-tubes, etc.) for heating liquid, but never dry, substances. The tubing used by the student for bending, blowing and fitting up apparatus should be of soft glass. Cutting the Tube. — Glass tube up to one-fourth inch in diameter may readily be cut by making a slight scratch with a triangular file at the point of fracture, the tube is now grasped firmly in both hands holding the scratch outward and the thumb nails pressed against the 6 HOUSEHOLD CHEMISTRY. inner side of the tube opposite the mark, give a slight bend outward, at the same time pulling apart; the tube will make a clean break and no injury will be received. Broken in this way the tube ends are sharp and should always be rounded by heating for a moment in the flame. Bending the Tube. — Take care that the tube is per- fectly clean and dry inside and outside before heating. Adjust the wing- top to the burner and after lighting, heat the tube lengthwise in the upper part of the flame. Revolve the tube so as to heat all parts equally; when soft, remove from the flame and quietly bend to the de- sired angle. In case no wing-top is available, the tube may be heated in the same way in an ordinary illumi- nating burner. The carbon deposited on the tube is readily removed, after cooling, by rubbing with filter- paper. Drawing the Tube. — Heat as before in wing-top or illuminating burner ; when soft, remove from the flame and quietly but steadily draw apart. On cooling, the tube may be cut with a file at any spot, and will furnish two pointed tubes. These are used for dropping tubes, by cutting to the desired length and rounding the ends in the flame. Closing the Tube and Blowing Small Bulbs. — Select a tube with thick walls, cut off a piece about a foot long, heat the square-cut end in the upper part of the ordinary Bunsen flame, revolving the tube continuously while heating; in a short time the tube will close. To blow a CONSTRUCTION AND USK OF TH:^ WASH-BOTTI.K. ^ bulb continue the heat for a few minutes longer, then re- move and blow quietly but strongly into the open end of the tube, continue the air pressure until the desired diameter has been reached, but on no account attempt to make a bulb of more than double the diameter of the original tube, as in this case the walls will be too thin. If it has been impossible to blow a bulb of the desired size in one operation, the tube may be reheated and blown again until the desired diameter has been reached. Glass rod may be cut, bent and rounded in manner similar to tubing. CONSTRUCTION AND USE OF THE WASH=BOTTLE. Select a clean eight-ounce wide-mouthed bottle, fit to it a rubber stopper pierced with two holes. Now cut two pieces of one-fourth-inch glass tubing, six and ten inches long, heat the longer piece in the wing-top flame about three inches from the end, when soft remove from the burner and bend to an angle of 45°. Heat and bend the shorter piece in the middle to an angle of 135°, round both ends of each tube in the flame, when cold moisten one end of the short tube with saliva and push it through one hole of the stopper, proceed in the same way with the longer tube but push it nearly up to the bend, so that when the stopper is inserted in the bottle the other end will just clear the bottom. Cut a piece of black rubber tubing two inches long, slip one end over the longer tube, make a jet by cutting off two inches of the pointed end of a dropping tube, round the rough end, 8 HOUSEHOI.D CHEMISTRY. and when cool push it into the rubber tube. The bottle is complete and ready for filling with cold water. By blowing into the short tube, a fine jet of water will issue from the nozzle; by tipping the bottle upside down, a larger stream will issue from the shorter tube. Wash-bottles for hot liquids are made in the same way^ using a thin glass flask instead of a bottle. CARBON AND COriBUSTION. Wood contains moisture (H^O), resin (CxH^), starch and cellulose (CgH^oOj), oil (CxH^OJ, mineral matter or ash. Considerable heat is required to drive off the moisture and raise the starch, cellulose, etc., to such temperatures that they will decompose, yielding gases of a com- bustible nature; for example, CO, CH^, C2H^,C2H2, Hg; in this decomposition H^O is formed and must be driven off as a gas, much heat is also absorbed by the ash in form- ing new chemical compounds. In fact the fuel efficiency of wood depends entirely upon the relative volumes of combustible gas and charcoal furnished, and as the charcoal or carbon is the best solid fuel, the wood furnishing the largest proportion of carbon in this form is the best fuel, hence we find it advantageous to use hard wood. It must be understood that carbon or char- coal at a red heat combines with a limited amount of oxygen and forms a combustible gas, carbon monoxide, CO, a fuel of the highest heating efficiency. Coal is superior to wood as it contains less water and CARBON AND COMBUSTION. 9 produces less by chemical change and yields the com- bustible gases and carbon (coke) in larger proportion. Hard coal is superior to soft, since it is a purer form of carbon and yields no combustible gas. Gas is superior to any solid fuel, as it has no water to vaporize and no ash. Gas containing CH„ C^H,, and C2H, is called illuminating gas and does not produce the heating effect of fuel gas composed of H, and CO. Even when both are used in the Bunsen burner, a glance will show that one will produce a large amount of H^O by combustion, while the other does not, and as water absorbs much heat, that producing the least amount will absorb the least heat. The reactions taking place will be given under the Bunsen and common burners. Destructive Distillation. — Make a capillary tube as directed, and insert it in a perforated cork. Now place in a hard glass test-tube small pieces of hard wood, in- sert the cork and clamp the tube and contents in a slightly inverted and inclined position on the ring-stand. Gently heat the tube in the flame, from mouth upward. From time to time try the exit tube with litmus paper, and then with the flame, continue the heating until the pieces of wood appear to be completely charred, but avoid burning the cork. Before allowing the tube to cool, carefully remove the cork, collect any liquid in the tube in a small dish, and close with a fresh cork. Observe the odor and general character of the liquid and test with litmus paper. When the tube is cool remove the charred material, carefully observe its character with lO HOUSKHOI.D CHKMISTRY. a magnifying glass, and make a rough sketch of its structure, float a small piece on water, and boil it for ten minutes, try another piece in the flame, burn another piece in a porcelain dish. Is there any residue ? If so, note its character. Repeat the same experiment using bituminous, and anthracite coal. Note any difference in the products of distillation of soft coal and wood. Arrange the results of these experiments in tabular form. Behavior of Mixtures of Gas and Air. — Fill a 250 cc. wide-mouthed bottle with about four-fifths air and one- fifth gas, collecting it over water, cover with a glass plate and shake thoroughly. Quickly replace the glass plate with wet filter-paper, pierce with a pencil point, apply the flame and note the result. Try the same ex- periment, using gas alone. Products of Combustion. — Hold a clean dry flask filled with cold water over a Bunsen flame and note the result. What compound is formed ? Explain. Substitute a pointed glass tube for the Bunsen burner, turn the gas low and light at the point, introduce the flame into a clean dry bottle and hold it there for a few moments, note the result and remove the tube. Again introduce it under the same conditions and note the result. Remove the tube, cover the bottle with a glass plate and turn off the gas. Pour about 10 cc. of lime- water into the bottle, shake well, note the result, explain and write the equation. ASH OF COAL OR WOOD. II The common burner can use gas of only the following composition, /. e., methane, CH^, ethylene, CgH^, acety- lene, C^H^, hydrogen, Hg, carbon monoxide, CO, and combustion proceeds according to the following equations : CH, + 20, ^ CO, + 2H2O heat, no light. 2H, + O, ^H^O *' '' " 2CO + O2 =2C0, " ♦* ** C^H, + O2 = 2H2O + C2 less heat, some light. 2C3H, + O, =2H30 + 2C, " *' more '' The Bunsen burner mixes the gas with O, before com- bustion; this change afifects only the ethylene and acetyl- ene, as follows : C^H, + 3O2 = 2H2O -f 2CO, heat, no light. 2C,H, + 50, = 2H,0+4CO, '' " '' ASH OF COAL OR WOOD. Wood Ash. — Burn a small piece of hard wood or char- coal on platinum foil until thoroughly ashed, cool and transfer to a small porcelain dish, add a small quantity (5 cc.) of distilled water, and heat to boiling. Is there any residue? If so, note its character. Filter, if necessary, and test the filtrate with red and blue litmus paper, dip a clean platinum wire in the solution and then heat it in the Bunsen flame ; observe the color with and without blue glass. Coal Ash. — Burn a portion of pulverized coal on platinum foil until completely ashed (this may take some time during which other experiments may be 12 HOUSEHOLD CHEMISTRY. proceeded with). Cool and treat the ash with 5 cc. of distilled water, filter, test the filtrate as above, treat the residue with warm, dilute hydrochloric acid (HCl), uote the character and amount of residue from the latter treatment. Test a portion of the hydrochloric acid solution in a test-tube as follows : 1. For lime (CaO). By adding ammonium hydroxide (NH^OH) until alkaline, and then an equal bulk of ammonium oxalate, and heat to boiling; a white crystalline precipitate indicates lime. 2. For iron (Fe203). Test the remainder of the solu- tion for iron, by adding to the test-tube of liquid a few drops of ammonium thiocyanate (NH^SCN); a red color indicates iron. A more elaborate method for analysis of ash is given on page II. LIQUID FUELS. Note. — On account of the highly inflammable nature of the following compounds very small amounts must be taken for tests, and particular care exercised with the use of the naked flame. Naphtha and Gasoline. — Pour not more than one or two drops of the liquid into a clean dry eight-ounce bottle, stir the vapor with a hot glass rod, withdraw the rod and apply a light, note the result. Pour the same quantity of liquid into a shallow porcelain dish and immediately appl}^ a flame, note the result and explain the difference in the two phenomena. I.IOUID FUELS. 13 Pour 20 drops of the liquid into a flat watch-glass, allow it to stand and note the time of evaporation and the quantity of the residue, if any, (Test for the presence of water. ) Gasoline or naphtha should be neutral; try it with delicate litmus paper. Kerosene.— Gently heat a small cup half full of the oil over hot water, and note the temperature at which inflammable vapor is given off ; this is called the flash- point and is a valuable indication of the quality of the oil. Try the reaction with litmus paper. This compound is called an oil; heat a little with strong caustic lye; does it make soap ? Paraffin. — Heat a small lump of paraffin in a clean, dry porcelain dish over a low Bunsen flame and note the flash-point as before. Heat a portion with caustic lye; does it saponify ? Compare and explain the differ- ence in inflammability of gas, kerosene and paraffin. Make mixtures of small portions of clean tallow or lard with cold gasoline and kerosene and with heated paraffin; filter the liquids if not clear and carefully evaporate small portions of each on the water-bath. Compare the residues with the original substances. Ex- plain the action of these solvents in removing grease spots. Make mixtures of equal quantities of gasoline and cold water, kerosene and cold water, and melted paraffin and warm water in small corked test-tubes, shake well 14 HOUSEHOI.D CHEMISTRY. and observe their condition. Now allow the tubes to rest quietly for ten to fifteen minutes then carefully open each and note the condition and position of each. Try the specific gravity of kerosene and naphtha with the hydrometer. WATER. Physical Properties. — i. Pour 250 cc. of water into a small round-bottomed flask, introduce a thermometer so that the bulb is immersed in the liquid and apply heat. Note the point at which the thermometer rises when the liquid boils quietly. Raise the thermometer just out of the liquid. Is there any change ? Does the thermometer indicate any higher degree of heat when the water is boiling violently ? 2. Repeat the experiment after dissolving a table- spoonful of salt in the water, and note the point at which the liquid now boils. Save this liquid for future use. (Expts. 7 and 13). 3. Note the boiling-point of a mixture of equal volumes of water and alcohol. 4. Select a cork which fits the flask, pierce a hole through it sufficiently large for a thermometer, and half fill the flask with pure water. Boil the liquid and when it is in active ebullition, close the flask with the cork fitted with the thermometer and withdraw the heat. In a few minutes the liquid will cease to boil. Watch the thermometer. Pour cold water on the outside of the flask until boiling is resumed and watch the thermometer. Explain the result. WATER. 15 5. Place a fresh egg in cold distilled water and note how much salt must be dissolved in it before the egg floats. Explain this phenomenon. 6. Heat a flask containing about 250 cc. of fresh cold tap water over the double boiler or water-bath. Observe the air bubbles which collect on the sides of the vessel and also the highest temperature of the water obtained by this method. 7. Take a portion of salt solution prepared in Experi- ment 2 and boil it down to one-half of its original bulk in a small beaker; note with a thermometer the point at which it boils, and make frequent readings of the thermometer until the desired bulk is reached, then re- move the thermometer and allow the liquid to cool thoroughly; examine the result with a lens and draw what you see. Taste it; does it suggest the original salt? 8. Make a strong solution of cane-sugar in water, treat it in the same way as the salt solution, and record your results. 9. Take half a teaspoonful of dry pulverized lime (CaO), add to it a teaspoonful of cold water, stir the mixture in a porcelain dish with a thermometer, adding more water if necessary, record the thermometer readings carefully, at the conclusion of the experiment, wash the material into a wide-mouthed bottle, fill up with distilled water, cork and shake well, let stand until clear and then carefully pour away the hquid, add more water, cork and shake well again, reserve for future use. The second 1 6 HOUSEHOLD CHEMISTRY. clear solution is called lime-water, (Ca(0H)2), and is much used in the laboratory and household as a mild alkali; try it with litmus paper, also taste the clear liquid. 10. Take a tablespoonful of common plaster, mix with half the volume of water, in a porcelain dish, stirring as before with a thermometer. Read the thermometer as the mass hardens. Record the result and compare with Experiment 9. 11. Slowly pour about 10 cc. of strong sulphuric acid (H2SO4) into 50 cc. of cold water, stir well with a ther- mometer and from time to time record the temperature. 12. Carefully mix exactly nine volumes of alcohol (C2H5OH) and one volume of water ; how many volumes result ? Record and explain. 13. Add two or three drops of the liquid from Experi- ment 2 to 100 cc. of water and filter; is any change pro- duced ? Now add to the filtrate a few drops of silver nitrate (AgNOg) shake well and filter again; note any difference. 14. In eight ounces of water dissolve enough copper sulphate to give the resulting liquid a distinct but not deep shade. Filter a little of this; what is the result ? Reserve the bulk for Experiment 15. What inferences do you draw from Experiments 13 and 14? 15. Distillation of water. A. Place on a wire gauze or sand-bath and make firm with a clamp, a round-bottomed half-liter flask con- taining about 250 cc. of the liquid made in the preceding experiment. Insert in the flask a cork fitted wdth a WATER. 17 thermometer and a 45° exit tube and connect this latter with a straight tube air condenser. Begin the distilla- tion, taking note of the boiling-point of the liquid. Examine carefully the distillate, and see if you can detect any trace of copper sulphate. Also test with phenolphthalein. B. Cool the apparatus and add ammonia to the liquid in the flask until a clear, deep blue solution is obtained, cork and distil again, testing as before. Note the differ- ence of behavior of the volatile and non-volatile com- pounds. Instructions for Making a Simple Filter and Opera- ting the Same. — Take a clean colander, lay in it a piece of well-boiled muslin and cover with a layer of clean boiled sea-sand one to one and a half inches deep. Filter the sample of boiled water through this; if once is not enough, repeat. Some waters are stained brown or yellow by vegetable matter and contain finely divided clay; in either case add a small quantity of alum (point of the small blade of a pen-knife) to the gallon of water, heat slowly to boiling, and then filter. The muslin and sand may be used many times, but be- fore each operation should be treated as follows : Scald the cloth and heat the dried sand at least thirty minutes in a hot oven. Qualitative Examination of Water.— No attempt will be made to give methods for quantitative analysis of 1 8 HOUSEHOLD CHEMISTRY. the impurities found in water, but certain qualitative tests which will aid in detecting such impurities, when present in abnormal amounts, and it is only when found in abnormal amounts that the water is open to suspicion. The impurities are for the most part harmless in them- selves, and a thorough investigation of the surroundings and sources of contamination of the water supply, care in taking the sample, and other precautions are quite essential. The tests usually made are : Color and appearance, odor and taste, and for the presence of total solids, free and albuminoid ammonia, nitrogen as nitrites and nitrates, chlorine, temporary and permanent hardness, and sometimes phosphates, sulphates, etc. Total Solids. — Evaporate to dryness in a clean porcelain dish loo cc. (about three ounces) of ordinary drinking- water. Examine the residue if any, and notice if it blackens on heating. This indicates organic matter. Phosphates may be determined at this point by adding to the residue a little water, nitric acid and ammonium molybdate. If phosphates are present, a yellow crystalline precipitate will be formed on heating to body temperature. Ammonia. — Two forms of ammonia are looked for in water, the ' ' free ammonia' ' and the so-called ' ' albuminoid ammonia." Free Ammonia. — This is determined by distillation as in Experiment 15, omitting the copper sulphate and ammonia, and testing each 20 cc. of the distillate with WATER. 19 Nessler's solution which gives a yellow or brown color in the presence of ammonia. Continue until a portion is found which fails to respond to the test; at this point the water is ammonia-free. Albuminoid Ammo?iia. — This is ammonia derived from organic matter, by means of alkaline permanganate of potassium. It may be applied to the water already in the flask from which the free ammonia has been ex- pelled, or to a fresh sample, in which case you obtain the total ammonia and deduct the free ammonia. Test. — In either case, add to the water in the distilla- tion flask 10 or 15 cc. of alkaline permanganate, boil and test the distillates as before with Nessler's solution. Note the difference in the amount of ammonia set free. Nitrites. — The presence of nitrites in water is supposed to be due either to the reduction of nitrates already pres- ent in the water by the action of organic matter, or to the oxidation of organic nitrogen to nitrite. Test. — To about 25 cc. of water in a large test-tube, add 5 cc. of freshly prepared mixture of equal parts of sulphanilic acid dissolved in acetic acid, and of naphthyl- amine acetate dissolved in dilute acetic acid, mix and allow to stand for about thirty minutes. If the solution becomes pink, the water contains nitrites. Compare with a sample of water known to be nitrite-free. Chlorine. — Chlorine is found mostly as sodium chloride, although other chlorides may be present. Test. — Place in a small casserole or porcelain dish 20 HOUSEHOLD CHEMISTRY. about loo cc. of tap water, and in another dish the same amount of distilled water. Add to each, two or three drops of potassium chromate solution, then add, drop by drop, a dilute solution of silver nitrate, (N/io) stirring after the addition of each drop, until a faint tinge of red appears in the liquid. Obtain the same tint in each and note the number of drops of silver nitrate used in each case. The difference between the two shows the amount of chlorides present. Each drop of silver nitrate solution is equivalent to 0.00279 gram of sodium chloride. Hardness. — By hardness is meant the soap-destroying capacity of a water. This property is due principally to the fact that calcium and magnesium salts form, with ordinary soaps, insoluble compounds or soaps which separate as a curd in the water and have no detergent value. The hardness of a water may be classified under two heads, viz., " Temporary" and " Permanent." Temporary Hardness. — Temporary hardness is caused by the carbonates of calcium and magnesium held in solution by carbonic acid present in the water. Boiling expels the carbon dioxide, causing the precipitation of calcium and magnesium carbonates. Dilute 10 cc. of clear lime-water to 50 cc, place the mixture in a large test-tube and pass a rapid current of carbon dioxide (made from marble and dilute nitric acid) through the liquid. Carefully observe the changes in the liquid and when perfectly clear stop the passage of WATER. 21 the gas. Now transfer the liquid to a small low flask fitted with stopper and double bent glass tube, the longer leg of which should project into a test-tube of lime- water. Boil the contents of the flask violently for- some minutes, but keep the lime-water cool. Carefully note and explain all changes in the contents of flask and tube. Finally cool the flask and filter off the clear liquid, pass carbon dioxide through this as before, and explain the difference in behavior. Note the condition of the walls of the flask; why will not water remove the crust ? Try dilute acid and watch its action. What is the crust ? Test. — Place loo cc. of tap water in an eight-ounce bottle and add a solution of pure castile soap (lo grams dissolved in dilute alcohol), 0.5 cc. at a time, shaking thoroughly after each addition, until a lather is formed which lasts five minutes. Note the amount of soap solution used. Now boil 100 cc. of the same sample and repeat the test, noting again the amount of soap solution used. The difference gives the temporary hardness. Permanent Hardness. — Permanent hardness is caused by the presence of calcium sulphate and other soluble salts of calcium and magnesium, not carbonates, held in solution by the solvent action of the water itself; such a water cannot be materially softened by boiling but may be softened by boiling with sodium carbonate, which converts the sulphates, etc., into carbonates and precipi- tates them as such. 22 HOUSEHOI.D CHEMISTRY. Dissolve O.I gram of plaster (calcium sulphate) in loo cc. of distilled water, pass a rapid current of carbon dioxide through the solution and continue at least as long as in the case of lime-water. Why is the action not the same ? Finally add sodium carbonate solution and note the result. Explain. Some waters possess both temporary and permanent hardness, in which case the total hardness is first deter- mined; the water is then boiled and the permanent hard- ness determined and then the temporar}^ hardness obtained by difference. THEATnOSPHERE. Composition. — Pure air is mainly composed of four parts of nitrogen and one part of oxygen. Other constitu- ents occur in small quantities, chief of which are water and carbon dioxide. Oxygen is a colorless, odorless, tasteless gas, slightly soluble in water. It supports combustion, combines with all the elements except fluorine, during the operation heat and sometimes light is evolved. Oxygen supports life and maintains the animal heat by combining with the carbon and hydrogen of the food materials. It acts as the great disinfectant and deodorizer, destroying many bacteria. Nitrogen is a colorless, odorless, tasteless gas, almost insoluble in water, does not support life or combustion, is non-poisonous, and does not cloud clear lime-water. It acts as a diluent of the atmospheric oxygen and to some extent as food for plant life. THK ATMOSPHKRS. 23 Carbon dioxide is a heavy gas, colorless, tasteless, odorless, product of combustion of carbon, but does not support life or combustion; is non-poisonous, soluble in water, forming carbonic acid (a weak acid), and the solution clouds clear lime-water. It is the main food for plants, enabling them to produce starch with the aid of moisture and sunlight. 600^ + sH^O = CgHjoO^ + 60,. The excess of oxygen is returned to the atmosphere. Part of the COg dissolves in water and combines with CaO (Hme) furnishing shells of moUusks and finally limestone, marble, chalk and various other useful carbonates. H2O is a colorless, odorless, tasteless liquid at ordinary temperature, solid at 32° F., gas at 212° F., volatile at all temperatures, without change of composition, is a univer- sal solvent, food, does not mix with ordinary fats and is more dense. Wood floats in it, metals do not. Iron rusts in contact with water. It is neutral, i. e., neither acid nor alkaline. Oxygen and nitrogen have nearly the same density and are mechanically mixed in air, the mixture is maintained by constant movement (wind currents). Oxygen with- drawn by animals and combustion is replaced by plants, some carbon dioxide is withdrawn by rain, which washes out other impurities. Excess of moisture is removed by fall of temperature, in the form of rain, hail, snow, and dew. Oxygen, O^. — Pour one inch of alkaline pyrogallol into a short, broad test-tube, close with a rubber stopper, in- vert and mark the position of the stopper and liquid on a 24 HOUSEHOI.D CHEMISTRY. gum label pasted on the outside of the tube; now shake the tube well, invert and open under water, mark the level of the water in the tube when open, and explain the phenomena. Carbon Dioxide, CO^, and Nitrogen, N^. — Fasten one inch of Christmas candle to a flat cork, float on a shallow dish of lime-water, light the candle and invert a clean dry beaker over it; add more lime-water if necessary. Describe and explain the result. Try a lighted candle in the residual gas; what is the result ? Explain. Carbon Dioxide, CO^. — Expose a few drops of lime- water on a slide to the air and notice that by the end of the lesson it is cloudy. Examine under the microscope the rhombohedral crystals of calcium carbonate (CaCOa) and draw a diagram of them. Hydrogen Sulphide, H^S.— Moisten a filter-paper with a solution of acetate of lead and expose to the air until the end of the lesson. Notice the black coloration due to the formation of lead sulphide. This test works very well in gas-lit rooms. rioisture. — (i) Expose a strip of dry cobalt chloride or cobalt iodide paper to the air and at the end of the lesson note the change in color. (2) Expose a little calcium chloride (CaCL) on a watch-glass, let it remain until the next lesson and note any change. Dust and Solid Matter. — Put a drop of glycerin on a THE ATMOSPHBRK. 25 slide, place it outside the window and examine under the microscope at the next lesson. Ferments. — Expose about a teaspoon ful of weak sugar solution in a test-tube for about one hour, then loosely plug with cotton and examine it at the next lesson as to taste, odor and appearance. Place a drop on a slide and examine under the microscope. Food Principles consist of carbohydrates, fats, proteids and mineral matter. Carbohydrates. — Compounds containing C, H and O, the H and the O in the proportion of 2 : i and the C 6 or some multiple. Examples of these compounds are starch, cellulose, glucose, sugar, etc. Composition of Carbohydrates. — White sugar is used since it is the purest commercial carbohydrate. 1 . Determination of Hydrogen and Oxygen Evolved as Water. — Heat about i gram of granulated sugar in a clean dry test-tube. Observe the condensation of mois- ture in the cooler part of the tube. 2. Determination of Carbon. — (a) By direct heat, continue heating and note the blackening of the mass due to freeing of some of the carbon, {b) By dehydra- tion, treat about i gram of the sugar in a porcelain evaporating dish with a little concentrated sulphuric acid, heat gently and note the blackening effect. In this case the concentrated sulphuric acid withdraws the hydrogen and oxygen in the form of water and leaves the carbon. 26 HOUSKHOI.D CHEMISTRY. 3. Determination of Hydrogen and Oxygen in the Form of Hydrocarbons, i.e., Tarry Bodies. — Observe the pungent odor of the vapors arising from the tube during the heat- ing in Experiment 2, (a). This usually condenses on the cooler part of the tube in the form of a dark brown liquid (caramel). (STARCH, C,H,A)..- Ordinary Starch Derived from Potatoes or Corn. — i. Examine a thin section of potato under the microscope. Make a careful drawing of the structure of the cells and the granules within. Cover the section with a thin glass and introduce a minute trace of iodine solution at the edge of the cover glass. Note, and make a colored (blue pencil) diagram of the result. 2. Clean and peel one end of a small potato, rub it on an ordinary grater, collect the gratings in a beaker of cold water, allow the whole to stand for some minutes and examine the sediment. 3. Gently heat half an inch of dry starch in a clean, dry, six-inch test-tube, observe and explain the condensed moisture in the cooler part of the tube. Increase the heat somewhat and note the odor of the evolved vapor and the color of the starch; what does it suggest ? Now heat strongly until only a black residue remains; what is it? 4. To a small portion of dry starch in a porcelain evaporating dish add a few drops of concentrated STARCH. 27 sulphuric acid; note the result and after a short time heat gently and observe again. 5. Treat a small portion of finely pulverized dry starch with cold water, filter a portion and examine the filtrate for dissolved material, by evaporating a little on platinum foil; also by the iodine test. 6. Boil the remainder of the starch and water mixture; it gelatinizes. Filter some of this and test the clear, cold filtrate with iodine, explain. To the remainder when cool add a minute portion of iodine solution; it is colored blue. Gently heat this and allow to cool again; note the result. Now boil for some time, cool, the color does not return. Examine under the microscope portions of raw and cooked starch, with and without iodine. 7. To some starch solution in a test-tube add a small portion of caustic soda solution (NaOH) and a few drops of iodine solution and note the result. Repeat the ex- periment using dilute sulphuric acid instead of NaOH. 8. Add a solution of tannic acid to some starch solu- tion. Note the result, also any change effected by heat- ing. 9. Starch, a Colloidal Substance. — Prepare a dialyzer as directed and partly fill it with starch solution, then stand the whole in a beaker of cold water. After stand- ing for some time test the water for starch with iodine solution. 10. Make a verj- weak solution of starch in about eight ounces of boiling water ; to half of this solution add 28 HOUSEHOLD CHEMISTRY. 20 drops of strong hydrochloric acid and boil until clear, replacing the water lost by evaporation. At this point a small quantity of the cooled solution should give no blue coloration with iodine solution. If this is not the case add 10 drops of the same acid and boil some minutes longer, or until a small portion gives no test with iodine as above. Now neutralize the remainder of the solution with sodium carbonate solution. Prepare a Fehling solution by mixing 5 cc. of copper sulphate and 5 cc. of alkaline Rochelle salt with 20 cc. of distilled water and boil the solution exactly two minutes. During this period no change should take place in the liquid. Now add I or 2 cc. of the neutralized starch solution and boil again for two minutes. Note the change in color of the liquid and, when cool, the red precipitate of cuprous oxide, indicating the presence of a reducing sugar, /.