NRLF B M ESM 7fl3 flB! REESE LIBRARY __n~n_rv UNIVERSITY OF CALIFORNIA. , 790 . JO. Class No. j Accession No. i-u-Ti-u-u-u-u-u-u-u-u LABORATORY EXPERIMENTS ON THE CLASS REACTIONS AND IDENTIFICATION OF ORGANIC SUBSTANCES. BY ARTHUR A. NOYES, PH.D., ASSOCIATE PROFESSOR OF ORGANIC CHEMISTRY IN THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY, AND SAMUEL P. MULLIKEN, PH.D., INSTRUCTOR IN ORGANIC CHEMISTRY IN THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY. SECOND, rHOTf9&&-KtrriSED EDITION. E ASTON, PA.: CHEMICAL PUBLISHING Co. 1898. COPYRIGHT, 1897. BY ARTHUR A. NOYES AND SAMUEL P. MULLIKEN. PREFACE. THIS collection of laboratory experiments in organic chemistry has been prepared especially for the use of the classes of the Massachusetts Institute of Technology, as a supplement to the ordinary course of instruction in prepar- ation work. The authors' experience has shown that the preparation of typical organic substances in accordance with the plans followed in the manuals of Gattermann, Levy, Fischer, etc., teaches satisfactorily the manipulative methods of organic chemistry and the manner of execution of the leading synthetic processes, but that it fails, to a surprising extent in the case of most students, to give a knowledge of the important characteristics of the vari- ous classes of organic compounds, and therefore of the fundamental principles of the science. Unless the instruc- tor is continually on the alert, the course of preparation work becomes almost unavoidably a routine following of directions. Although the primary purpose of the experiments here described is to illustrate the characteristic reactions of or- ganic compounds, their analytical significance is a feature of no slight importance ; for, both in research and technical work, the chemist has frequent occasion to identify the sub- stances he meets with. On this account, and also because it is always desirable to make evident to the student some practical use of the information presented to him, the an- alytical side of the experiments has been made prominent ; and an important part of the course consists in the iden- tification of unknown compounds and the quantitative sep- aration of mixtures by methods devised by the student himself with the help of the knowledge gained from the experiments with known substances. 4 PREFACE. It is believed that the entire omission of explanatory statements of what occurs in the experiments will cultivate the student's power of observation, and cause him to con- sider more carefully the principle illustrated ; while the work on the identification and separation of unknown substances will afford abundant opportunity for original thought. It is assumed that a brief course of lectures on the outlines of or- ganic chemistry has preceded the laboratory experiments. Owing to the great importance, in the opinion of the authors, of instruction of this kind, and owing to the fact that no text-book presenting it exists, it has not seemed advisable to postpone the publication of the general plan, although it is undoubtedly imperfect in many matters of detail. The authors desire to express their indebtedness to Dr. J. F. Norris for many valuable suggestions, and to Messrs. H. M. Loomis, A. P. Norris, and C. L. W. Pettee, for their investigations on the applicability of many of the important tests. EXPERIMENTS ILLUSTRATING THE CLASS REACTIONS OF ORGANIC COMPOUNDS. Introductory Explanations and Directions. THE following experiments serve to illustrate some of the most important properties and reactions of the various classes of organic compounds. The results ob- tained are to be regarded as characteristic of the whole class as defined by the heading above the experiment. It must, however, be clearly understood that all com- pounds of the class do not give these Reactions with equal facility that, indeed, complex members of the class, and especially those belonging at the same time to two or more classes, often do not give them at all. Moreover, many of the reactions are general for more than one class; but, when this is true, it will be pointed out, as far as practicable, in the notes following the experiments. Statements of what occurs are omitted from the following directions ; and the student is expected to observe carefully and record fully in the note-book everything that happens, even those things of appar- ently minor importance. Attention should be directed not only to what may be seen, but also to any odor or to any heat effect developed. The observed phenom- ena should then be fully explained with reference to the new compounds formed ; and all the reactions where known products are formed should be written, 6 ORGANIC LABORATORY EXPERIMENTS, using structural formulae. Works on organic chemis- try should be consulted when necessary. The notes following the experiments must be very carefully studied. After completing the experiments, make a table in the note-book showing, as far as possible, the behavior of each class of compounds towards each of the follow- ing reagents : cold dilute alkaline hydroxides ; boiling concentrated alkaline hydroxides ; concentrated sulphu- ric acid alone and with subsequent addition of water ; sodium ; and bromine water. Students are warned that many of the reactions may take place suddenly and with great violence, and that, therefore, cautious manipulation is neces- sary, particularly in test-tube experiments. Behavior of Organic Substances on Ignition. 1. Ignite in a small crucible, as long as any change occurs, first a little benzoic acid, and then a little starch. Repeat the experiment with a little anhydrous so- dium acetate. Add a drop of dilute hydrochloric acid to the residue after cooling. This reaction with hydrochloric acid is given only by organic salts of the alkalies and alkaline earths. Detection of Water in Organic Liquids. 2. Add 0.2 gram of fused pulverized potassium car- bonate to 5. cc. of common 95 per cent, alcohol. Shake and set aside for an hour. Repeat this experiment, using 5 cc. of the same alcohol diluted with 1 cc. of water. 3. Add 0.5 gram copper sulphate, freshly dehy- drated by ignition at a low temperature, to 5 cc. of CLASS REACTION'S. 7 ordinary 95 per cent, alcohol. Shake and allow the mixture to stand for about one hour. Reactions Distinguishing Double and Triple-Bonded from Single-Bonded Compounds. ~~>y f ^ 4#. Dissolve 0.5 gram of amylene in 5 cc. of carbon J^l/. - ..tetrachloride, and add gradually a 10 per cent, solution ] a^L- of bromine in carbon tetrachloride as long as any action . occurs. J^ Repeat this experiment, using first cinnamic acid^^N^ then phenol, and finally toluene, in place of the amy- lene. In the cases of the cinnamic acid and toluene, after allowing the mixture to stand in the cold for two or three minutes, heat it to boiling for about a minute. Decolorization without evolution of hydrobromic acid shows addition, and therefore the probable presence of a double or triple bond. Decolorization accompanied by evolution of hydro- bromic acid shows substitution; but it does not necessarily ex- clude the possibility of a simultaneous addition, which may even be inferred in case the evolution of hydrobromic acid is not pro- portionate to the rate of decolorization. If even on heating no action occurs, or if only a slow action accompanied by evolution of hydrobromic acid takes place, it is probable that no double or triple bond is. present; it is true, nevertheless, that there are some double-bonded compounds (for example, fumaric, maleic, and the nitro-cinnamic acids) which form addition-products only very slowly or not at all under the conditions of this experiment. On the other hand, amines, phenols, and most aldehydes and ke- tones, like double-bonded compounds, decolorize the ^bromine so- lution instantly; -in the case of amines, often without evolution of hydrobromic acid. 4. Dissolve 0.5 cc. of allyl alcohol in 5 cc. of water, and gradually add bramine water as long as decoloriza- tion takes place. 8 ORGANIC LABORATORY EXPERIMENTS. Repeat the experiment, using ethyl alcohol instead of allyl alcohol. As bromine water is used as a reagent in other cases, this experiment is introduced here, in order to show its behavior with unsaturated compounds. But, as a means of distinguishing them from saturated bodies, the test in carbon tetrachloride is far more satisfactory: for, when water is used as the solvent, any hydro- bromic acid formed is absorbed by it, so that it is not readily possible to distinguish substitution from addition; moreover, be- sides these two actions, oxidation often takes place in aqueous solution ; and finally, the unsaturated compounds which fail to react in carbon tetrachloride are almost equally inert in water, so that the latter solvent has no advantage in this respect. 5. Add 0.2 gram of cinnamic acid to 5 cc. of so- dium carbonate solution, and then add drop by drop about 1 cc. of a one per cent, solution of potassium permanganate. Repeat the experiment, using first amylene and then toluene in place of the cinnamic acid. The oxidation takes place almost instantaneously with unsatu- rated compounds, and with some saturated ones, such as formic acid, malonic ether, phenols, oxybenzoic acids, benzaldehyde, ace- tone, acetophenone, glycerine, and some sugars. But most satu- rated compounds are oxidized much more slowly, if at all. Reactions of Triple-Bonded Compounds Containing the ( = C H) Group. 6. Add 1 cc. of ammoniacal cuprous chloride solu- tion to 10 cc. of a saturated aqueous solution of acety- lene and shake. Behavior Distinguishing Saturated Fatty Compounds Containing No Complex Alky I Radicals from Other Compounds. 7. Roll a piece of fine copper gauze 1 cm. square around the end of a copper wire. Dip this in succes- CLASS REACTION'S. 9 sion into small tubes containing (a) toluene, (b) ben- zoic acid, (c) allyl alcohol, (d) sugar, (e) ethyl ether, and (/) amyl alcohol. (In the case of the solid sub- stances, take care to make a considerable amount adhere to the gauze.) Hold the substance in a gas flame until it takes fire ; then remove it, and note whether soot is produced, holding a piece of white paper behind the burning substance. Almost all aromatic compounds, hydrocarbons, unsaturated fatty compounds, and fatty compounds containing alkyl radi- cals with four or more carbon atoms, when they can be burnt as here described, produce soot in considerable quantity. Other fatty compounds under the same conditions produce, as a rule, no soot. Behavior of Hydrocarbons in General. 8. Add 1 cc. of toluene first to 5 cc. of water, and then to 5 cc. of dilute sodium hydroxide solution (1 : 10), and shake. Many solid aromatic hydrocarbons are heavier than water. 9. Add a thin slice of sodium to a few cubic centi- meters of toluene in a perfectly dry test-tube. In the case of solid substances or in case only a slight effervescence occurs, the test should be made as illustrated by the following experiment. 10. Fill a small test-tube completely with anhy- drous alcohol-free ether; drop to the bottom a thin slice of bright sodium (3 cm. long, 1 cm. wide) ; and insert at once a clean, dry rubber stopper, through which passes a small glass tube which reaches nearly to the bottom of the test-tube and is there turned upwards for a distance of a few millimeters, and which is bent above the stopper so as to deliver into another test-tube. Allow the action to continue 10 ORGANIC LABORATORY EXPERIMENTS. for fifteen minutes, and make a mark on the tube to show the amount of gas produced. Dissolve 1 gram of naphthalene in a test-tube full of the same ether, and repeat the above experiment. The ether for this experiment will be found in the laboratory. It is prepared by washing commercial ether eight or ten times "with small quantities of strong salt solution, drying it for at least one day over a large quantity of calcium chloride, treating through several days with successive portions of sodium, and finally distill- ing over sodium with every precaution to avoid access of moisture. The product should be kfept over sodium in a bottle provided with a drying tube. Reactions Distinguishing Hydrocarbons of the MetJianc (C n H 2n + 2 ) from Those of the Benzene (C n H 2n _ 6 ) Series. - 11. Thoroughly mix together by shaking in a wide test-tube 2 cc. of petroleum ether and 5 to 6 cc. of w fuming sulphuric acid (sp. gr. 1.89 at 20). Pour the mixture very slowly and cautiously into three volumes of cold water, and allow it to stand a few minutes. Repeat this experiment, using toluene instead of petroleum ether. 12. Repeat both parts of Experiment 11, using fuming nitric acid (sp. gr. 1.48) in place of sulphuric acid. As the action may suddenly become very vio- lent, great care must be taken to hold the tube in such a position that its contents cannot be thrown out upon the experimenter. In the case of entirely unknown substances, very small quan- tities should first be experimented with. CLASS REACTIONS. 11 Behavior of Halogen-Substituted Hydrocarbons. 13. Add 1 cc. of ethyl bromide first to 5 cc. of water," and then to 5 cc. of dilute sodium hydroxide solution, and shake. The monochlorinated derivatives of the fatty hydrocarbons are lighter than water. X Reactions Distinguishing Halogen Compounds of Differ en t Types . 14. Add three drops of ethyl bromide to 5 cc. of an alcoholic solution of potassium hydroxide (free from chlorine), and boil gently for two minutes. Di- lute with water, acidify with nitric acid, and add a few drops of silver nitrate solution. Repeat this experiment, using first benzyl chloride, and then brombenzene in place of the ethyl bromide. In experimenting with unknown substances, in order to make sure that they contain no free halogen or halogen acid, it is advis- able to wash them with dilute sodium carbonate solution before applying the test. The behavior of ethyl bromide is typical of halogen com- pounds of the fatty series; that of benzyl chloride, of aromatic compounds containing halogen in the side chain; and that of brombenzene, of aromatic compounds having halogen attached to an aromatic nucleus. Some halogen compounds of the lat- ter class, especially those containing also a nitro group, are de- composed by potassium hydroxide and give the reaction with silver nitrate. Reaction Distinguishing Saturated and Aromatic Hy- drocarbons and Their Halogen Derivatives from Other Compounds. 15. Add gradually, shaking constantly and keep- ing the mixture cool, 4 cc. of concentrated sulphuric 12 ORGANIC LABORATORY EXPERIMENTS. acid to 2 cc. of (a) toluene, (b) ethyl bromide, (c) phenol, and (d) ethyl acetate. The behavior with cold sulphuric^acid will generally distin- guish saturated and aromatic hydrocarbons and their halogen derivatives from other compounds, most of which are either soluble in the acid or are destroyed by it. Among these other compounds there are, however, many which are unacted upon by sulphuric acid, but these exceptions are met with mostly among the acids and nitrogen compounds. The test is therefore espe- cially useful in distinguishing hydrocarbons and their halogen derivatives from alcohols, phenols, ethers, and esters. Reactions of Compounds Containing the Hydroxyl Group. 16. Add small pieces of sodium to 3 cc. of abso- lute alcohol, in a test-tube, as long as it dissolves. The sodium should be added fast enough to keep the solution hot without causing it to boil violently. Finally, cool the solution. Substances to which this test is to be applied must first be thoroughly dried, if water is present. Solid or viscous sub- stances must be dissolved in anhydrous ether or some other indifferent solvent. If the effervescence is only slight, the test must be tried as described in Experiment 10, in order to form an idea of the amount of gas evolved, and thus distin- guish a slow action on a hydroxyl compound from that due to an impurity. Besides hydroxyl compounds, some aldehydes, ketones, esters, and amides evolve hydrogen ; and the halogen compounds of the lower hydrocarbons of the ,fatty series give off gaseous hydro- carbons. On the other hand, a few hydroxyl compounds (for example, resorcin, and salicylic acid) fail to give evidence of a reaction with sodium. Reactions of Alcohols and Phenols. 17. Add gradually 2 cc. of amyl alcohol to 4 cc. of concentrated sulphuric acid in a small test-tube, shak- CLASS REACTIONS. 13 ing constantly and keeping the mixture cool. Allow it to stand two or three minutes, and then pour it into a test-tube containing about 12 cc. of water. Repeat the experiment, using phenol in place of the amyl alcohol. In the case of the higher fatty alcohols a layer consisting of the original alcohol or some insoluble reaction-product may separate out on the dilution of the sulphuric acid. Compare Experiment 32. If the substance to be tested is soluble in water, it is not possible to determine in this simple manner whether or not it combines with the sulphuric acid. In that case the method illustrated by the following experiment must be employed. 18. Mix 2 cc. of strong sulphuric acid with 5 cc. of alcohol. After five minutes pour the mixture into 100 cc. of water, heat to boiling, and add barium car- bonate until the liquid is neutral. Filter hot. Add dilute sulphuric acid to one-half of the filtrate. Evap- orate the other half to dryness and ignite the residue. Of the alcohols, only the primary ones of the fatty series give the reactions observed in this experiment Phenols and some other aromatic compounds, however, give apparently the same result, owing to the formation of soluble sulphonic acids and soluble barium sulphonates 19. Add 2 cc. of acetyl chloride to (a) 1 cc. of ethyl alcohol and (b) 1 gram of phenol, and add the mixtures to 5 cc. of water. Use great caution, as the reactions with acetyl chloride are sometimes very violent. Reactions of Alcohols. 20. Test the solubility of ethyl alcohol and of amyl alcohol in water and dilute sodium hydroxide solutions. All monoatomic alcohols containing less that four atoms of carbon and almost all polyatomic alcohols are readily soluble in water; other alcohols are insoluble or difficultly soluble. 14 ORGANIC LABORATORY EXPERIMENTS. 21. Place in a small flask 2 cc. of alcohol, 50 cc. of sodium hydroxide solution (1 : 10) and 5 cc. of ben- zoyl chloride. Shake until the odor of benzoyl chlo- ride has disappeared. Repeat the experiment, omitting the alcohol. The odor observed in this experiment is a characteristic and delicate test for the lower monoatomic alcohols of the fatty series. Hydroxyl compounds in general, with the exception of acids, un- dergo a similar reaction ; but the products do not possess the same characteristic odor. Reactions of Phenols. 22. Test the solubility of phenol in water, in so- dium carbonate solution, and in sodium hydroxide solu- tion by adding the solvents little by little to 1-2 grams of the substance. Test the solubility of resorcin in water. Test the reaction of the aqueous solutions with alkaline phenolphthalein solution or with blue litmus paper. 23. Add a few drops of ferric chloride solution to solutions of phenol, of pyrocatechin, and of resorcin. .This test is applicable to neutral solutions only. In order that it may be regarded as indicating the presence of a phenol, a strong coloration must be obtained; for most hydroxyl deriva- tives give a faint yellow coloration. The most important phenols that fail to give this reaction are a-naphthol, the nitrophenols, and meta and para oxyacids. On the other hand, many aromatic amines give similar colorations; and oxyacids of the fatty series give a strong yellow coloration (compare Experiment 30). 24. Heat together in dry test-tubes for one or two minutes in an oil-bath at a temperature of 150, 0.2 gram phthalic anhydride and a somewhat smaller quan- tity of phenol, a-naphthol, resorcin, and pyrocatechin, the mixtures being first moistened (not covered) with a CLASS REACTIONS. 15 few drops of concentrated sulphuric acid. Treat the fused mass with 10 cc. of cold water, and add so- dium hydroxide solution very gradually until no fur- ther change occurs. Dilute portions of the faintly alkaline solutions, and view them obliquely from above by reflected light. 25. Add bromine water to 5 cc. of phenol solution until the liquid assumes a permanent yellow color. This reaction is a very delicate one for most phenols, but there are a few exceptions. Moreover, many aromatic amines also give a precipitate with bromine water. Reactions of Organic Acids. 26. Test the solubility in water of benzoic acid and oxalic acid. Nearly all acids containing more than six carbon atoms, ex- cept the aromatic sulphonic acids, are insoluble or very difficultly soluble in cold water. On the other hand, nearly all of the acids commonly met with containing a smaller number of carbon atoms are soluble. 27. To about 0.2 gram of benzoic acid add, in por- tions of 1 cc. at a time, a one per cent, solution of so- dium hydroxide strongly colored by the addition of a little phenolphthalein solution. In order to distinguish between considerable amounts and accidental traces of acids, the test is made in this way, so as to determine roughly the quantity of alkali required for the neutralization. Some esters are so readily saponified that they cause, when tested as here described, a rapid decolorization of the solutions ; but the action is never instantaneous, as is the case with most acids. 28. Treat 1 gram of benzoic acid with 5 cc. of water; add sodium carbonate solution, at first in small 16 ORGANIC LABORATORY EXPERIMENTS. quantity, and finally in slight excess ; then acidify with ^hydrochloric acid. 29. Add 20 cc. of sodium formate solution (1 : 5) to 0.5 gram (weighed approximately) of the following acids in the state of fine powder : Benzoic, salicylic, phthalic, cinnamic. All these acids are nearly insoluble in water. The experi- ment determines roughly the strength of the various acids as compared with formic acid. Those stronger than formic acid displace it and go into solution ; those weaker do not. The strength of acids depends on their composition and structure. Of the aromatic acids, the sulphonic acids and the derivatives of benzoic acid and its homologues containing one or more nitro groups, or two or more halogens, or one halogen, hydroxyl or carboxyl group in the ortho position to the carboxyl group, are stronger than formic acid. Acids containing none of the men- tioned "negative " groups, or containing one halogen in the meta or para position, or one or more hydroxyl groups in the meta or para position, are weaker than formic acid. (For a detailed list of the strengths or "affinity constants " of various acids see the Zeitschrift fiir physikalische Chemie, 3, 418.) Reaction of a-Oxy-acids. 30. Dissolve 0.1 gram of tartaric acid in 50 cc. of cold water, in a porcelain dish, and add two drops of a 10 per cent, ferric chloride solution. Repeat the experiment, using sugar in place of tar- taric acid. As is illustrated by the latter part of this experiment, hy- droxyl compounds in general give a slight coloration ; but the color produced by the a-oxy-acids is very much stronger at the same concentration. It is, moreover, always a pure yellow. Reactions of Ethers and Esters. 31. Add 1 cc. of ethyl ether first to 5 cc. of water, and then to 5 cc. of dilute sodium hydroxide solution. CLASS REACTIONS. 17 Repeat the experiment, using amyl acetate in place of ethyl ether. 32. Repeat Experiment 17, using first ethyl ether and then amyl acetate in place of amyl alcohol. Reactions of Compound Ethers or Esters. 33. Boil vigorously over a small free flame 3 cc. of ethyl benzoate with 80 cc. of potassium hydroxide solu- tion (1 : 4) in a 200 cc. long-necked, round-bottomed (Kjeldahl) flask provided with a long return cooler of wide bore, until the odor of the ester disappears. Acid- ify half the solution with an excess of hydrochloric acid. Dilute the remainder with water to 100 cc., add 5 cc. of benzoyl chloride, and shake till its odor has disap- peared, as in Experiment 21. Since the ease of saponification varies greatly with the nature of the ester, the boiling should be continued until complete solu- tion takes place, or until the ethereal odpr disappears. If the alcohol of the ester is insoluble, and if the acid of it is soluble in water, evidently the ester would not be detected by the method illustrated by the above experiment (except, perhaps, by the disappearance of its odor). In case, therefore, the above test gives a negative or indecisive result, proceed as in the fol- lowing experiment. 34. Introduce into a long-necked, round-bottomed flask of 200 cc. capacity 50 cc. of a 6 per cent, alcoholic potassium hydroxide solution measured accurately by means of a pipette. Add to it 3 c. of ethyl acetate. Connect the flask in an inclined position with a return cooler, and boil vigorously for twenty minutes. Rinse off the condenser and stopper into the flask, dilute to about 100 cc., add a drop or two of phenolphthalein 18 ORGANIC LABORATORY EXPERIMENTS. solution, and titrate with hydrochloric acid (one part acid of 1.12 sp. gr. to two parts of water) added by means of a graduated pipette. Titrate in the same way 50 cc. of the original alcoholic potassium hydroxide solution. In case of unknown substances, if an appreciable amount of acid is found to be present by the test described in Experiment 27, it must first be removed by washing the substance with so- dium carbonate solution, and then with water. Aromatic aldehydes are also converted by potassium hydrox- ide into alcohols and acids. Moreover, amides, nitriles, some carbohydrates, and a few ketones are decomposed with formation of acids which combine with the potash. Reactions of Acid Chlorides. 35. Add a few drops of water to 1 cc. of acetyl chloride. It is generally necessary to heat acid chlorides in order to produce this decomposition. Reactions Common to Aldehydes and Ketones. 36. Test the solubility of benzaldehyde in water and in dilute sodium hydroxide solution. The lower aldehydes and ketones of the fatty series are, however, readily soluble in all these solvents. Acetaldehyde is converted by alkalies, especially on heating, into aldehyde-resin, a brown amorphous substance. In regard to aromatic aldehydes, see the note to Experiment 34. Cold concentrated sulphuric acid either dissolves or destroys aldehydes and ketones. 37. Shake together for two or three minutes 3 cc. of acetone and 5 cc. of a saturated solution of sodium acid sulphite. If necessary, set aside and cool. This reaction, while very characteristic, is not particularly delicate. Ketones give it only when they contain the group -CH 3 .CO. Solid substances should be dissolved in a very little CLASS REACTIONS. 19 ether. In applying the reaction to unknown substances, always test the reagent first with a portion of acetone. 38. To 5 cc. of aldehyde solution add an equal volume of sodium acetate solution and a few drops of a solution of phenylhydrazine hydrochloride. This test is, as a rule, most satisfactorily applied in aqueous solution, most aldehydes and ketones being sufficiently soluble in water for the purpose. In some cases, however, it is neces- sary to use some other solvent than water; but in that case a negative result is not decisive, since the hydrazone formed may be soluble. Reactions of Aldehydes (not Ketones}. 39. Mix in a test-tube previously cleaned with hot sodium hydroxide solution 1 cc. of ammoniacal silver nitrate solution and 1 cc. of ten per cent, sodium hy- droxide solution. Shake the mixture about in the tube, and then allow two or three drops of aldehyde solution to flow slowly down the moistened glass surface. Do not warm the mixture. This test is known as the Tollen's reaction for aldehydes. The ammoniacal silver solution contains one part of silver nitrate dissolved in ten parts of ammonia water of sp. gr. 0.923. When mixed with sodium hydroxide, a dangerously explosive precipi- tate is apt to form on heating or on long standing. Some compounds other than aldehydes, especially di-atomic and tri-atomic phenols and amidophenols, reduce ammoniacal sil- ver solution. 40. Pour two or three drops of aldehyde solution into 5 cc. of cold fuchsine-aldehyde-reagent. This aldehyde-reagent is prepared by dissolving one part of a rosaniline salt in one thousand parts of water, and then adding enough of a strong sulphurous acid solution to destroy the red color on standing. An excess of sulphurous acid does not inter- fere with the reaction. Some ketones when added to the reagent in relatively large quantity give the same reaction as aldehydes ; but the change occurs much more slowly. 20 ORGANIC LABORATORY EXPERIMENTS. Reaction for Carbohydrates. 41. Add to pieces of sugar, starch, and filter paper not larger than a mustard seed 0.5 cc. of water, two drops of a 20 per cent, alcoholic solution of a-naph- thol, and 2 cc. of concentrated sulphuric acid. Dilute with water and add a slight excess of potassium hy- droxide solution. The composition of the compound formed is unknown. The tests for aldehydes and ketones described in the pre- ceding experiments are, as a rule, not applicable to carbohydrates. Reactions of Aromatic Nitro-Compounds. 42. Add 1 cc. of nitrobenzene to 5 cc. of water, to 5 cc. of dilute hydrochloric acid, and to 5 cc. of dilute sodium hydroxide solution. Nitro-compounds, particularly those containing two or more nitro groups, color sodium hydroxide solution deep red or yellow. 43. Repeat Experiment 17, using nitrobenzene in place of the amyl alcohol. Trinitro-compounds and many other nitro-compounds contain- ing other substituted groups require heat for their solution in sulphuric acid. 44. To 1 cc. of nitrobenzene, in a wide test-tube, add 23 grams of granulated tin ; and then add, in sev- eral small portions, 5 cc. of hydrochloric acid of 1.2 sp. gr., with constant shaking. The temperature and the addition of the acid should be regulated so as to secure a moderate reaction. In order to complete it, gentle heat and the addition of more tin or acid may be necessary. Pour the clear solution into a beaker, dilute with 10 cc. of water, and add potassium hydrox- ide solution (1 : 2), until the solid precipitate formed at first has for the most part redissolved. CLASS REACTIONS. 21 44A. Dissolve three drops of .nitrobenzene in 3 cc. of 50 per cent, alcohol. To this solution add five or six drops of calcium chloride solution (1 : 10) and a pinch of zinc dust. Heat until the mixture begins to boil briskly, and then, after allowing it to stand from two to five minutes, filter. Add the filtrate to a strongly ammoniacal silver nitrate solution. -Nitroso, azo, and azoxy compounds also give this reaction. It is, of course, useless to apply it to compounds that reduce silver nitrate before treatment with zinc dust. The compound formed in the above experiment by the action of the zinc dust on nitrobenzene is phenyl hydroxylamine. The effect of the calcium chloride is to accelerate the reduction. 44e. Dissolve three drops of nitrobenzene in 3 cc. of a light-colored mixture of equal parts of aniline,