UC-NRLF Elementary Organic Analysis P.G, BENEDICT The Chemical Publishing Co. Elementary Organic Analysis. Elementary Organic Analysis The Determination of Carbon and Hydrogen BY FRANCIS GANG BENEDICT, PH.D., Instructor in Chemistry in Wesleyan University EASTON, PA.: THE CHEMICAL PUBLISHING CO. 1900. COPYRIGHT, 1900, BY EDWARD HART. B PREFACE Perhaps no analytical operation is at once so funda- mentally important and exasperatingly vexatious as the organic combustion. Notwithstanding this fact } save for the meager statements in one or two of the larger books on organic chemistry, no description of the process of the determination of carbon and hydro- gen is accessible to most students. As a rule a knowl- edge of * the operation is chiefly obtained by word of mouth. This little manual is presented in the hope that the descriptions of processes here recorded will aid in making this method of analysis more familiar and more satisfactory. Usually very little, if any, discrimination is exer. cised in burning the compounds obtained in organic research, and experiment alone is relied upon to secure the proper conditions for complete combustion. It is hoped that the different cases cited in the latter part of the manual will aid in giving some clue to the treat- ment necessary for many compounds, thereby saving time and, more frequently, valuable material. While an attempt has been made to describe all op- erations commonly used it is obviously impossible not to give fuller consideration to such modifications of the general method as have been suggested by an ex- perience with over two thousand combustions. Ac- vi PREFACE cordingly these modifications are treated in detail and as a general rule recommended in preference to the older manipulations. For the painstaking care and numerous suggestions of Mr. Emil Osterberg, assistant in this laboratory, whose experimental skill has contributed greatly to many of the modifications here presented, the writer is extremely grateful. MIDDI.ETOWN, CONN. TABLE OF CONTENTS Introduction i Preparation of oxygen 2 Compressed oxygen - 3 Gasometers or gas-holders - 6 Air - ii Purifying apparatus 12 Rubber tubing and stoppers 1 7 Combustion furnaces - 18 Combustion tubes 21 Oxidizing agents 24 Filling the combustion tube - - 27 Boats - 29 Absorbing agents - 31 Absorbing apparatus 33 Cleaning and weighing absorbing apparatus - 42 Weight of material used 45 Burning out the combustion tube - 45 General process of the combustion 49 Combustion of nitrogenous substances 58 Combustion of bodies containing the halogens f 65 Combustion of bodies containing sulphur - 68 Combustion of bodies containing the alkali metals 70 Combustion of difficultly combustible bodies - 70 Combustion of liquids and volatile bodies - 73 Combustion of explosive bodies 80 Calculation of results - 80 Appendix 82 Index - 83 INTRODUCTION The analysis of organic compounds requires the de- termination of but few elements, the most important of which are carbon, hydrogen, and nitrogen. This book has to do only with the determination of carbon and hydrogen in organic compounds. The method consists of converting all the carbon to carbon dioxide, all the hydrogen to water, and absorbing and weigh- ing these products. In bodies containing nitrogen, care is taken to pro- vide that none of its compounds are retained in the systems used to absorb water or carbon dioxide. In general the nitrogen escapes in the gaseous form. The oxidation of the carbon and hydrogen may be effected by mixing the material intimately with me- tallic oxides, such as cupric or mercuric oxide, or with oxygenated salts, such as potassium chlorate, potassium dichromate, or lead chromate. In some methods use is made of a current of air or oxygen to facilitate the burning of refractory substances and to regenerate the oxidizing agents. The property of platinum and pal- ladium of condensing large quantities of oxygen on the surface of the finely-divided metal has also been made use of in conjunction with the current of oxy- gen to effect the combustion of organic substances. The method best adapted for general purposes involves the use of cupric oxide and a current of air or oxygen. In this last method all volatile organic products are 2 ELEMENTARY ORGANIC ANALYSIS oxidized by a layer of hot cupric oxide ; and air, or better, oxygen is finally introduced to aid in oxidizing any charred residue and to reoxidize the reduced cop- per. Of the products formed, water is absorbed by calcium chloride or sulphuric acid ; carbon dioxide is absorbed by a solution of potassium hydroxide or by soda-lime ; and the nitrogen, if present, escapes as such from the tube. PREPARATION OF OXYGEN The commonest method of preparing oxygen is by heating a mixture of potassium chlorate and manganese dioxide. The two ingredients should be separately pulverized and, if necessary, dried. Equal weights of each are intimately mixed and heated in a 250 cc. Jena glass Erlenmeyer flask, fitted with a stopper and a wide glass elbow, and clamped on a retort stand. To the elbow is attached a rubber tube with a glass elbow at the other end which permits a free movement of the tube in the pneumatic trough or gasometer. On grad- ually increasing the heat a rapid though steady evo- lution of oxygen is obtained. At the end of the re- action and before the lamp is removed the tube must be withdrawn from the pneumatic trough or gasome- ter to prevent the back suction of the water. If glass other than Jena is used the flask should be protected in heating with a piece of asbestos paper. The purity of the manganese dioxide is of consider- able importance as an admixture of carbonaceous mat- ter of any nature is liable to cause an explosion, be- COMPRESSED OXYGEN 3 sides contaminating the oxygen with carbon dioxide. It is accordingly advisable to test a small portion of the mixture by heating it in a test-tube. COMPRESSED OXYGEN The use of compressed oxygen for elementary or- ganic analysis is especially to be recommended as fur- nishing a constant, ready supply of the gas. 1 It is fre- quently necessary to refill a gasometer during a com- bustion, particularly if there is any considerable leak- age, and it is not always possible to prepare the gas quickly according to any of the methods ordinarily in use. A cylinder of the compressed gas can be used at any time to refill the gasometer or, what is still more advantageous, to supply the oxygen to the tube with- out the use of a gasometer. Progress in the compressed gas industry has reached such a point that it is comparatively easy to secure a strong, thoroughly well-tested cylinder of highly-com- pressed oxygen. These cylinders are made in all sizes, containing from a few gallons to a hundred cubic feet of oxygen. For the laboratory, a cylinder containing ten cubic feet or seventy-five gallons is of convenient size. The gas thus compressed contains slight traces of carbon dioxide, water vapor, and nitrogen, but the most vexatious impurities existing in compressed oxy- gen are volatile hydrocarbons resulting from the su- perheating of the oils used in lubricating the com- 1 J. Am. Chem. Soc., 21, 389. 4 ELEMENTARY ORGANIC ANALYSIS pressing machinery. With compressed oxygen con- taining these impurities a preheating furnace 1 is neces- sary to oxidize the hydrocarbons. Some manufacturers have replaced the lubricating oils with graphite and in the large number of cylin- ders of compressed oxygen obtained from the S. S. White Dental Mfg. Co., of Princes Bay, N. Y., and tested in this laboratory, gaseous hydrocarbons, or at least hydrocarbons not completely absorbed by the sulphuric acid of the drying apparatus, 2 were never detected. Only compressed oxygen free from hydrocarbons is recommended as the preheating furnace is an unde- sirable addition to an already elaborate apparatus. The gas obtained from the above-mentioned source is com- paratively dry and, after being freed from traces of moisture and carbon dioxide, is sufficiently pure to be used in elementary organic analyses. A cylinder containing ten cubic feet costs about ten dollars. The so-called "commercial" oxygen, which differs from the "medical " only in so far as it has been, perhaps, a little less thoroughly washed and purified, costs at the rate of ten cents per foot; i. e., one dollar per ten cubic feet. This amount is not great com- pared with the cost of an ordinary Mitscherlich or Pepy gasometer. Inasmuch as the gasometers are used almost exclusively to hold oxygen, it will be seen that they are not indispensable to the ordinary laboratory supplied with a cylinder of the gas. Ten cubic feet 1 J. Am. Chem. Soc., 15, 531. * See page 14. COMPRESSED OXYGEN will last for a great many carbon and hydrogen com- bustions, while the advantage of using a cylinder of this gas in the lecture room is obvious. Inasmuch as the oxygen contained in the steel cyl- inders is under great pressure, some method of regu- lating the flow of gas as it en- ^ ters the combustion tube must be devised. The expensive pre- cision and reduction valves used ordinarily with these cylinders can be replaced by the follow- ing simple arrangement. A rubber tube leading from the cylinder connects with a T-tube, one end of which dips one inch under mercury in a small bot- tle fitted with a rubber stopper having two holes (Fig. i). The second hole is left open. A rubber tube connects the other end of the T-tube with the puri- fying apparatus, which is in turn connected by rubber tubing to the combustion tube. This last rubber tube is sup- plied with a pinch-cock which Fig- i- is closed. When the valve . on the oxygen cyl- inder is opened slightly the gas will flow out, and, passing through the trap, produce a bubbling in the mercury. As yet no gas escapes through the purify- ELEMENTARY ORGANIC ANALYSIS ing apparatus. If, now, one wishes to regulate the flow of gas, the pinch-cock is opened until the desired rate of flow is secured. Any excess of gas still escapes through the mercury trap. It is always possible to adjust the valve on the oxygen cylinder finally, so as to prevent any appreciable loss of oxygen through the mercury. As the weight of the cylinder, as well as that of the oxygen it contains, is generally given, by keeping a record of the weight of the cylinder it is easy at any time to determine how much oxygen remains. If a high pressure gauge is at hand a similar result may be obtained by recording the diminution in pressure. 1 GASOMETERS OR GAS-HOLDERS Where the air or oxygen used is not under pressure L in cylinders or pipes connected with a constant supply, some form of gasometer is necessary. A Pepy gasometer (Fig. 2) con- structed of zinc or preferably of copper is less liable to be broken than the Mitscherlich or glass form though there is great advantage in being able to see at a glance the amount of gas remaining in the appara- tus. For elementary analysis alone the Pepy form has one Fig. 2. unnecessary pipe and stop-cock 1 Miiller: Ztschr. physik.-chem. Unterricht, 13, 26. GASOMETERS OR GAS-HOLDERS 7 (C) which is used to direct gas into cylinders filled with water and inverted in the upper vessel. The gasometer is filled with water by closing the opening near the bottom and opening all valves at the top and then conducting into the upper pan a current of water which flows through the connecting pipes and soon fills the lower chamber. The rise of the water is noted by means of the side gauge tube. When the gasometer is completely filled all the cocks are tightly closed and the screw plug or cock near the bottom removed. A little water will run out, especially if the chamber has not been completely filled with water. After the first few cubic centimeters have escaped no more water should run out and gas from a generator or cylinder may be conducted by means of a bent tube through the opening in such a manner that it rises inside the chamber, the displaced water running out at the opening. Consequently it is necessary in filling a gasometer of this form to conduct the operation at a: sink or to provide in some other way for the displaced water. When filled with gas the lower chamber is tightly closed and the upper pan is filled with water. On opening the stop-cock A, the water in the pan flows down through a tube extending to the bottom of the lower chamber until the internal pressure of the gas is sufficient to sustain the column of water in the tube. By carefully opening stop-cock B, gas may be with- drawn as desired. As gas is withdrawn the water flows through the valve A into the lower chamber and provision must be made to furnish occasionally a sup- 8 ELEMENTARY ORGANIC ANALYSIS ply of water for the upper pan as otherwise as soon as all the water in the pan has run into the lower cham- ber, the flow of gas would cease. Instead of intermit- tently adding water to the upper pan a simple device may be used for maintaining a constant level of water in the pan. This consists of a rubber tube conduct- ing water from a tap through a twenty centimeter length of small lead pipe, bent in the form of a U and hung over the edge of the pan. A hole is made in the side of the pan about half way down and a cork carry- ing a tube leading to the sink is carefully inserted. Water flowing through the lead U fills the pan to the level of the opening and all excess of water flows away through the overflow to the sink. The Mitscherlich form of gasometer is manipulated in es- sentially the same manner, the operation of the valves differ- ing in no way from that in the Pepy form. The adoption of the device for maintaining a constant level in the upper jar is rendered somewhat difficult, as a hole is not as readily made through glass as through metal. However, any one may, with a broken file and emery and camphor, grind a hole of suitable size through the glass. By slipping a piece of thick-walled rubber tubing over the glass tube used as an overflow it can be inserted in the orifice which accordingly need not be unnecessarily large. The use of gasometers of these forms is, however, open to considerable objection, for if constructed of metal they soon leak, owing to the attacks of acid fumes and vapors always present in a laboratory, and are constantly needing repairs, and glass gasometers, though they do away with the large mass of metal, rely on metallic pipes, cocks, and connections to re- GASOMETERS OR GAS-HOLDERS 9 ceive and deliver the gas. These connections are equally liable to the attack of acid, resulting in leak- age and consequent loss of gas. The fragile nature of such gasometers and the necessity for transportation to the sink, when being filled, make their handling difficult. Consequently it is only by exercising great care in the lubrication of stop-cocks and in the general treatment of this form of gas-holder that satisfactory service can be obtained. A much simpler though less convenient form of gas-holder (Fig. 3) consists of two carboys, demijohns, or large bottles Fig. 3- fitted with two-holed rubber stoppers through one hole of which a glass tube extends to the bottom of the vessel. The other hole in one of the stoppers is provided with a glass elbow carrying a short piece of rubber tubing and a screw cock. A rubber tube once and a half as long as the vessel is high, con- nects the two long glass tubes in the two vessels. One bot- tle is completely filled with water and the screw pinch-cock closed. The other is then lowered until its mouth is about on a level with the bottom of the bottle containing water. 10 ELEMENTARY ORGANIC ANALYSIS The delivery-tube of the gas generator from which only a gentle current 1 of oxygen must be escaping is connected with the short rubber tube, the screw-cock having been previously opened, 2 and the gas entering the bottle forces the water through the long rubber tube into the other bottle. At the end of the operation the gas generator is removed and the screw-cock immediately closed. By raising the bottle con- taining water to a position somewhat above the level of the bottle containing gas, almost any degree of pressure may be obtained. The gas is drawn off by slowly opening the screw pinch-cock. Bottles having tubulatures at the bottom are used with a one-holed stopper carrying, in the one case, a short glass elbow and screw-cock, while the hole in the other stopper is left open. The long rubber tube connects short pieces of glass tube thrust through stoppers in the tubulatures. The manipulation differs in no wise from that given. Another convenient form of gasometer is a modification of the foregoing, consisting, however, of only one vessel fitted with a two-holed rubber stopper, the holes of which are plugged with four centimeter lengths of glass rod or glass tubing sealed at one end. The vessel is filled with gas at a pneumatic trough and the stopper firmly inserted while the neck is still under water. The vessel is then placed on the table, one of the plugs withdrawn and a glass elbow, carry- ing a short piece of rubber tube and a screw-cock, quickly thrust into the hole in the stopper. A glass elbow in the end of a rubber tube connected to a tap is first filled with 1 Determined by dipping the tube for a moment under water in a beaker and noting the rate of bubbling. 2 The cock is opened and in case there was sufficient water in the long rubber tube to cause it to act as a siphon the action is momentarily stopped by pinching the connecting tube with the fingers, care being taken to release the pressure on the tube as soon as the oxygen generator is connected. By using care in filling the bottle no water is driven over into the rubber tube and the siphon is not started until the pressure of the gas in the generating apparatus forces the water up through the bend of the long glass tube into the rubber connecting tube whence it falls into the other bottle. AIR II water by allowing the water to flow through the tube for a moment, and then thrust into the second hole of the stopper after removing the plug. The connection is made between the rubber tube and the purifying apparatus and the screw- cock is opened. By admitting water through the glass elbow, gas in desired quantities may be forced through the system. If a three-holed stopper is used and a two or three centimeter layer of water is left in the bottom of the vessel a long glass tube may be thrust through the third hole far enough to dip under water in the bottom and thus serve as a pressure gauge. A fundamental objection to all forms of gasometers is the great inconvenience experienced in filling them at a sink with gas or water, requiring, as they do, transportation of a bulky apparatus filled with water. Accordingly whenever obtainable the use of pure com- pressed oxygen in steel cylinders is strongly recom- mended. AIR In some methods of analysis air is substituted for oxygen during the greater part of the combustion, oxygen being used only to oxidize refractory carbona- ceous residues. The use of air in gasometers is iden- tical with the manipulation described on page 7 with the exception that the filling is accomplished by open- ing the lower seal and the valve from which the gas is usually drawn at the top. For most organic bodies oxygen must be substituted for air before complete oxidation can be assured, hence two aspirators and puri- fiers are often used. Air under pressure may also be conveniently ob- tained from any of the numerous forms of water-blast. 12 ELEMENTARY ORGANIC ANALYSIS PURIFYING APPARATUS Impurities other than carbon dioxide and water- vapor are seldom present in oxygen or air used for analysis, though in the compressed oxygen furnished by some manufacturers material quantities of hydro- carbons are often present. These hydrocarbons are effectually removed by conducting the gas direct from the gasometer or cylinder through a heated glass, por- celain, 1 or brass 2 tube containing cupric oxide where they are oxidized to water and carbon dioxide. In general the removal of carbon dioxide and water-vapor only is necessary. The removal of water-vapor is effected by use of calcium chloride or concentrated sulphuric acid, while potassium or sodium hydroxide in sticks or in con- centrated solution, or soda-lime is used to remove all traces of carbon dioxide. The relative merits of the various absorbing agents are discussed at length under the head of absorbing agents on page 31. The essential feature of the purifying system is that it should hold a considerable quantity of the reagents and not become exhausted until after a large number of combustions. The gas entering the purifying ap- paratus is generally very moist from standing over water in a gasometer and contains but a small quan- tity of carbon dioxide. The gas leaving the combus- tion tube contains as a rule even more water and a great deal more carbon dioxide, so much more in fact 1 Dudley and Pease : J. Am. Chem. Soc., 15, 530. 2 Shimer: lbid.> ai, 560. PURIFYING APPARATUS 13 that the absorbing reagents ordinarily iised become exhausted after one or two combustions. Of the various absorbents of carbon dioxide and water the systems most commonly used are : Potas- sium hydroxide followed by calcium chloride ; potas- sium hydroxide followed by sulphuric acid ; sulphuric acid, potassium hydroxide, and sulphuric acid ; sul- phuric acid, potassium hydroxide, and calcium chlo- ride, etc., etc., and sulphuric acid, soda-lime, and sul- phuric acid. The last combination is remarkably efficient and hence is first considered. A simple form of purifying apparatus consists of a Drechsel gas washing-bottle one-third filled with con- centrated sulphuric acid, a U-tube containing soda- lime, 1 and a U-tube containing pumice stone drenched with concentrated sulphuric acid. The sulphuric acid in the bottle retains the water (in case a cylinder of compressed oxygen, which is itself very dry, is used, the gas washing-bottle with sulphuric acid may be discarded), the soda-lime retains the carbon dioxide, and the sulphuric acid and pumice stone U-tube the moisture escaping from the soda-lime. The gas issuing from this system is free from carbon dioxide and contains no moisture that can be retained by sulphuric acid. The three pieces of the absorber above described may be combined by using a calcium chloride jar filled as is shown in Fig. 4. 2 The tubulature should be as 1 Page 32. 2 Am. Chem . J., 23, 332. ELEMENTARY ORGANIC ANALYSIS near the top of the lower compartment 1 as possible, to permit the introduction of the maxi- mum quantity of concentrated sul- phuric acid. A piece of glass tubing of an ex- ternal diameter a little less than the internal diameter of the constriction in the jar is cut off long enough to rest on the bottom and reach within thirty millimeters of the top of the jar. A one-holed cork on the end of a glass rod is loosely inserted in the upper end of the tube and a layer of glass wool or long fiber asbestos is packed around the tube to a depth of three or four millimeters. Soda- lime prepared as described on page 32 and pulverized into pieces ap- proximately two millimeters in di- ameter is then introduced and the jar filled to within one centimeter of the top of the inner 1 Calcium chloride jars are furnished by Whitall, Tatum & Co. with the tubulature inserted at any point desired in the lower compartment at a cost but slightly in advance of the regular goods. As ordinarily made a jar " 12 inches high" will have the tubulature in such a position that about 20 cc. of concentrated sulphuric acid can be introduced without flowing out of the orifice or coming in contact with a rubber stopper inserted in the tubulature. Where gas from a cylinder of compressed oxygen is used this amount of acid suffices to dry a great many liters of gas, but if the gas is drawn from gasometers over water the reagent is more rapidly exhausted. Twenty cc. of acid will absorb effectually six grams of water and taking the temperature of a gasometer in use as 28 C., the gas leaving it would contain twenty-seven milligrams of water- vapor per liter. An average of 1.5 liters of oxygen are used per combustion in the method described beyond, hence twenty cc. of acid would serve for two hundred combustions, a number rarely exceeded by any one operator. The chief advantage of that form of jar having the tubulature near the top of the base is that there is much less liability of getting concentrated acid on the rubber stopper in the tubulature. Fig. 4. PURIFYING APPARATUS 15 tube. A " 1 2-inch" calcium chloride jar will require about one hundred and seventy-five grams of soda-lime. The layer of glass wool or asbestos prevents the soda- lime from falling through into the lower compartment. A long glass tube approximately ten millimeters external diameter is thrust through the one-hole rub- ber stopper inserted in the top of the jar. This tube is slightly constricted at the bottom and is filled with pumice stone which is subsequently drenched with concentrated sulphuric acid. The glass tube extends from about one centimeter above the cork to within two centimeters of the bottom and should be of a diam- eter small enough to slide easily through the upright tube passing through the constriction of the jar. The upper end of the tube is closed with a one-holed red rubber stopper carrying a glass elbow and a piece of rubber tubing with a screw pinch-cock. This stopper may be sealed with paraffin if desired. With this ar- rangement the only chance for leakage that could con- taminate the gas is in the stopper at the top of the glass tube. A leak at the other stoppers would be effectively counteracted so far as moisture (the great- est danger in leaks) is concerned by the long column of pumice stone and sulphuric acid. Concentrated sulphuric acid is poured down the central tube thoroughly drenching the pumice stone and collecting in the base. The first lot of acid is often contaminated with foreign material from the pumice stone and should be poured out of the tubula- ture; enough acid is then poured through the tube to 1 6 ELEMENTARY ORGANIC ANALYSIS fill the lower compartment to within five millimeters of the one-holed rubber stopper in the tubulature. The cork is then replaced in the tube and the pinch-cock closed. A glass tube bent downwards is thrust through the hole in the rubber stopper in the tubulature in such a manner that a current of gas passed through it bubbles through the acid in the base of the jar. The gas rises, passes through a long column of soda-lime at a very slow rate, and then turns and passes down through the annular space between the two glass tubes, finally en- tering the base of the tube filled with pumice stone and issuing at the top. The greater portion of the water is removed as the gas bubbles through the acid ; the carbon dioxide is completely removed by the soda- lime, and the unabsorbed moisture, including that lost from the slightly moist soda-lime, is removed as the gas passes over the pumice stone and sulphuric acid. The gas issuing at the top fs free from carbon dioxide and as free from moisture as is possible with sulphuric acid. In case the sulphuric acid becomes exhausted, to regenerate the purifier it is only necessary to drain the acid out of the lower compartment and pour fresh acid through the tube containing the pumice stone. This operation should be performed at the end of every fifty combustions. The soda-lime need not be renewed until it becomes three-fourths white. Numerous forms of apparatus, more or less complex, for holding the various absorbents for the purification of the air or oxygen used in organic combustions, are described in chemical literature and are furnished by most of the dealers in chemical supplies. Some are suited for the absorbing com- RUBBER TUBING AND STOPPERS 1 7 bination sulphuric acid, soda-lime, sulphuric acid and many were especially devised and are described as being filled with the other absorbents in any of the other combinations. Liquid reagents, such as potassium hydroxide solution or concen- trated sulphuric acid, are generally held in gas washing-bot- tles though sometimes they are poured over broken pumice stone in long U-tubes. Solid reagents, such as calcium chlo- ride, stick potassium hydroxide, and soda-lime, are generally placed in large U-tubes or calcium chloride jars. The re- markable absorptive power of soda-lime for carbon dioxide renders it unnecessary to have a great length of this reagent through which the gas must pass. RUBBER TUBING AND STOPPERS Rubber tubing is used to make all connections be- tween the oxygen supply, the purifier, and the com- bustion tube, and only fresh tubing, not cracked or deteriorated, must be used. Often strong sulphuric acid is carelessly allowed to suck back into the rubber tube connecting the supply of oxygen with the puri- fier. The tubing becomes hard and brittle and should immediately be removed. Red or maroon tubing, "5/32 inch " inside diame- ter, is a convenient size and withstands the action of heat better than most other kinds. A twenty to forty centimeter length is required to conduct the gas from the purifier to the combustion tube, but the gas issuing from the combustion tube does not come in contact with any length of tubing as it is advisable to have the glass tubes of the various absorbers touch, 1 using a two centimeter length of rubber tube simply to hold 1 Pfliiger : Arch. f. d. ges. Physiol., 18, 133 ; lyieben, cited in " Manual of Or " ganic Chemistry, " by L,assar-Cohn, p. 373 ; Berthelot : Compt. rend., no, 684. 2 1 8 ELEMENTARY ORGANIC ANALYSIS the glass tubes together. If glass touches glass a minimum exposure to rubber is obtained. The rubber stoppers used in the purifier and in the absorbing tubes may be of the ordinary quality though red rubber is preferable. Those used in the ends of the combustion tube ought to be of red rubber as it is much less affected by heat than any other kind. COMBUSTION FURNACES The accuracy demanded in organic elementary analy- sis at the present day renders the use of a gas com- bustion furnace almost imperative. The earlier forms of charcoal furnace are occasionally used in localities where gas is not at hand, but they are not of sufficient importance to warrant special consideration here. Where illuminating gas is accessible any one of the numerous forms of furnace may be advantageously used. In general the furnace, which is about eighty centimeters long, consists of a series of twenty to thirty Bunsen burners provided with air as well as gas regu- lating devices, screwed into a gas pipe of size large enough to supply all the burners with sufficient gas, giving a heating length of about seventy-five centi- meters. The flames are generally confined and made to impinge on fire clay tiles in such a manner that the combustion tube is heated on all sides as evenly as possible. A good pressure as well as a good supply of gas is necessary and, owing to the great heat and the large quantity of the products of combustion, the furnace should be installed in a hood provided with a COMBUSTION FURNACES 19 good draft. Sufficient room for the gasometer or oxy- gen cylinder and the purifying apparatus as well as the absorbing system is necessary. A gas cock to which a Bunsen burner with a long rubber tube is attached should be at hand. The gas pipe with which the furnace is connected should be not less than " y- inch" standard size. Many designs of furnaces are in the market, each constructed with a view of attaining the greatest and most even heating of the combustion tube with the minimum consumption of gas. The progress made in developing the combustion furnace is not as great as the complex nature of many designs would indicate, and there is very little, if any, choice in the selection of a furnace. All are a great improvement on the charcoal furnace, and all have their salient points. As a rule the increase in complexity of construction and in cost is not accompanied by a proportionate increase in utility. Equally satisfactory results with the " Bun- sen," " Erlenmeyer-Babo," and u Glaser " furnaces have been obtained in this laboratory. The ' ' Glaser ' ' T furnace is provided with a series of iron U pieces placed side by side, forming a trough in which the combustion tube is placed. Difficulty is often experienced, however, as the pieces become separated and allow the free flame to impinge on the unprotected glass, a fracture of the tube being almost certain to result at the point of overheat- ing. If the tube is well protected at the bottom with two or three layers of asbestos paper the liability to accident is much decreased. 1 Ann. Chem. (I^iebig) Suppl., 7, 215. 20 ELEMENTARY ORGANIC ANALYSIS In most other forms of furnace, including the two others above mentioned, the combustion tube is laid in a heavy sheet iron or tile trough. Tiles possess the advantage of not becoming twisted or warped on heating, but owing to their fragile nature and their non-conductivity for heat, thus necessitating considerable time to heat and cool, they are not to be recommended. Iron troughs are open to the serious objection that they warp and twist and constantly form scales of iron oxide which clog the burners. On the other hand, they are very cheap, conduct heat much better than tile, and if constructed of sheet iron two millimeters in thickness do not warp sufficiently to cause any con- siderable difficulty. Any plumber or tinner can make them by hammering a piece of thick (two millimeters) sheet iron over a gas pipe. They may be renewed before any considerable amount of scale is formed and are on the whole the most satisfactory form of trough to use. The trough, whether it is of iron or tile, should be lined with two or three layers of asbestos paper which will protect the tube. A fifteen centimeter square of rather thick asbestos card having a two centimeter hole in the center is thrust over each end of the combustion tube as a pro- tection to the corks. The consumption of gas varies not only with the form of furnace, but more especially with the nature of the substance to be burned. A number of experi- COMBUSTION TUBKS 21 ments made with different forms of furnaces coupled direct to a gas meter gave an average consumption of forty-five cubic feet of gas per hour. In some forms of furnace, provision is made for rais- ing or lowering the burners which is often an advan- tage in securing the best regulation of the flames. The furnace should be raised some three or four centimeters at the anterior end by placing a block of wood of the required height under the support. (Fig. 12, p. 51.) COMBUSTION TUBES The cupric oxide used to oxidize the volatile por- tions of the material to be burned is heated in a plati- num, porcelain, or glass tube. Platinum tubes are expensive and consequently but rarely used. Porce- lain tubes are much used in technical work, but as a rule are too fragile and expensive for ordinary labora- tory use. Glass tubes are almost invariably used in all other than technical laboratories. As the old bayo- net form of tube originally used by Liebig has been almost universally replaced by the tube open at both ends, the former need not be considered here. The long-continued high heat to which a glass combustion tube is subjected requires that it be of glass of unusual resistance to heat, /. ., not melting easily and capable of withstanding rapid fluctuations in temperature. Bohemian glass An especially hard glass contain- ing potassium instead of sodium, i. e., Bohemian glass, has been used for this purpose with satisfactory results for a number of years. It is drawn in tubing of a con- 22 ELEMENTARY ORGANIC ANALYSIS venient size, generally from twelve to fifteen milli- meters internal diameter, designated as combustion tubing, which, unless otherwise ordered, comes in lengths of approximately two meters. Jena glass Recently a new glass of a remarkably high melting-point and small coefficient of expansion has been introduced which promises to prove of great value in organic analysis. A special kind of Jena glass, made expressly for combustion tubing, which must not, however, be confused with the softer glass used for preparing sealed tubes, furnishes a tube that leaves very little to be desired and which is nearly as resistant to heat as are the more expensive porcelain tubes. In this laboratory the average number of combus- tions made with Jena glass tubes is over fifty, while four tubes have withstood heating in ninety-seven, ninety-nine, one hundred and four, and one hundred and sixteen combustions respectively. Owing to its infusibility there is much less danger of breaking Jena glass tubes by fusion to tile or iron troughs, a source of many accidents with the other forms of glass. Fortunately the price of this glass is no greater than that of other kinds of combustion tubing. For use in the furnace the tube should be cut of a proper length and the sharp edges should be rounded to prevent their cutting the stopper and introducing bits of rubber which might easily be swept into the heated part of the tube. One end of the length of COMBUSTION TUBES 23 combustion tube should be cut off square, if it is not already so, and then a length equal to the length of the furnace plus ten centimeters 1 marked off with a file scratch on the glass. A sharp triangular file is necessary for the purpose. If a deep scratch is made the tube may readily be broken at the scratch in case it is of Bohemian glass by following a line around the tube in the direction of the scratch with a hot glass rod, or better with a gas flame burning from a fine jet. The gas flame is held in a tangential position and the tube rapidly revolved three or four times to produce excessive heating in a narrow band around the glass including the scratch. Then by directing the flame on the scratch for a few moments the crack will usually start and instantly run clear around the tube in the heated zone leaving a sharp cut. With Jena glass tubing it will be necessary to file a deep scratch clear around the tube. On applying the heat from a fine gas jet as described the tube is then cut with no great difficulty. After cutting the tube in the desired length the sharp edges of the cuts are rounded off either by filing with a round file or better by fire-polishing, i. e., par- tially fusing the edges in a blast-lamp. The fire-pol- ishing is done by carefully heating one end of the tube in a smoky flame of a blast-lamp until the glass is covered with soot. The air is then admitted to the blast-lamp and the temperature gradually increased 1 As the furnace is generally eighty centimeters long the glass tube is cut ninety centimeters, thereby allowing five centimeters to protrude at each end of the furnace. 24 ELEMENTARY ORGANIC ANALYSIS till the edges are fused. The cooling should be slow and is brought about by cutting off the air from the blast-lamp and gradually turning off the gas till the end of the tube is again covered well with soot. The flame is then extinguished and the tube allowed to cool in the air. The covering of soot equalizes the radiation of heat and prevents cracking. When cool the tube is carefully wiped and washed inside and outside with water and then rinsed with 10-20 cc. of alcohol which is allowed to drain out. The alcohol adhering to the walls of the tube is re- moved by rinsing with a few cubic centimeters of ether and the tube is then gently warmed by moving a Bun- sen burner along its entire length, removing the ether- vapor by a blast of air or by suction from a filter-pump. OXIDIZING AGENTS USED IN THE COMBUSTION TUBE Cupric oxide. The ease with which this compound gives up its oxygen to reducing substances renders it of the greatest value in organic combustions. For general purposes the wire form, consisting of short pieces of copper wire that have been completely converted to the oxide, is the best. This form is readily obtained in the market. Approximately four hundred grams of the oxide in the wire form are required to fill a combustion tube. Granular copper oxide obtained by igniting the ni- trate is often used. The powdered oxide is used in small quantities to cover highly refractory substances. Each time before being used it should be heated OXIDIZING AGENTS USED IN COMBUSTION TUBE 25 strongly in a Bunsen flame and then allowed to cool in a desiccator where it should be preserved. Both forms are readily obtained in the market. Spirals of copper oxide are used and are prepared by winding stout copper wire tightly around a glass tube of such a size that the finished spiral, some twelve centimeters long, can easily be inserted in a combus- tion tube. The wire is bent in a ring form at each end to facilitate its withdrawal. The spiral is then strongly heated in a Bunsen flame till the oil is all burned off and an outer coating of black cupric oxide is formed. It is then cooled and kept in a desiccator until used. Another form of spiral which is, however, more readily disintegrated, is prepared by rolling a piece of copper gauze, ten centimeters square, around a piece of stout copper wire some eleven or twelve centimeters long, with a loop made in each end. The wire gauze is compactly rolled and the roll when finished must easily slip into the combustion tube. The fine copper wire of which the gauze is made, read- ily oxidizes when heated in a flame which burns off any shellac, varnish, or oil. The brittle nature of the cupric oxide renders such spirals extremely fragile and they soon have to be replaced. Though presenting less surface of cupric oxide no difficulty will be experi- enced in using spirals of stout wire provided they are at least twelve centimeters long. Spirals of this form are often used to reduce oxides of ni- trogen when present as a product of combustion and are re- duced to the metallic form as described on page 64. 26 ELEMENTARY ORGANIC ANALYSIS A succession of spirals 1 has been used in place of the wire form of cupric oxide. Lead chromate is the only other oxidizing agent that is extensively used in ordinary methods of com- bustion. This material in the fused form is coarsely granulated and introduced into the combustion tube. It is used in burning substances containing sulphur or the halogens (p. 66). No special preparation is neces- sary as the material is furnished ready for use in the market. A mixture of nine parts of lead chromate and one part of potassium dichromate was introduced by Mayer, 2 but is not generally used. The low fusibility of lead chromate is the serious disad- vantage in its use and to obviate this difficulty De Roode 3 mixes one part of red lead with four parts of the chromate. A fused mixture of lead monoxide and cupric oxide was successfully used by Schwarz. 4 Platinized asbestos 5 and quartz, 6 asbestos covered with finely divided cupric oxide, 7 manganese sesquioxide, 8 mer- curic oxide, 9 potassium dichromate, I0 and potassium chlorate, " are occasionally used but belong rather to special methods. Other oxidizing agents that are occasionally used to cover refractory substances in a boat, are potassium dichromate, potassium chlorate, platinum sponge, and powdered cupric oxide. 1 Blau: Monatshefte, 10, 357. 2 Ann. Chem. (I,iebig), 95, 204. 3 Am. Chem. J., 12, 226. 4 Ber. d. chem. Ges., 13, 566. 5 Kopfer : Ztschr. anal. Chem., 17, 4. 6 Dennstedt: "Die Entwicklung der organischen JJlementaranalyse," p. 103. 7 lyippmann and Fleissner : Monatshefte, 7, 9. 8 Dudley : Am. Chem. J., 10, 433 ; Ber. d. chem. Ges., i, 3172. 9 Mitscherlich : Ztschr. anal. Chem., 15, 374; Frerichs : Ber. d. chem. Ges., io, 26. 10 Johnson and Hawes : Am. J. Sci., 7, 465. 11 Schulze : Ztschr. anal. Chem., 5, 269. FILLING THE COMBUSTION TUBE 27 FILLING THE COMBUSTION TUBE The tube cut to length, cleaned and dried as de- scribed on page 22, is filled by first inserting either a plug of previously ignited fibrous asbestos or a short copper oxide spiral five centimeters from one end of the tube (Fig. 5). 1 (((((I . f ' Fig- 5- The asbestos is best introduced by using a plunger consisting of a glass rod about ten centimeters long on the end of which is fastened a cork whose largest diameter is a little smaller than the internal diameter of the tube. The cork is inserted in the tube a dis- tance of five centimeters, crowding before it a small wad of asbestos. Holding the glass rod and the com- bustion tube firmly in a vertical position and keep- ing the cork five centimeters in the tube, the asbestos is packed down by a similar plunger with a long glass rod or tube inserted in the other end of the combus- tion tube. More asbestos is added, if necessary, till a plug eight to ten millimeters long is obtained. If cupric oxide spirals are used they must be prepared by rolling a strip of copper gauze, one centimeter wide and ten centimeters long, into a roll that will snugly fit the interior of the combustion tube. The roll should be thoroughly ig- nited in a Bunsen flame before being used . To the asbestos plugs there is the possible objection that a little longer time is required to oxidize all products of dry distillation that may be deposited on them in the course of a combustion, while with the cupric oxide spirals or rolls the 28 ELEMENTARY ORGANIC ANALYSIS oxidation of such material would be effected almost imme- diately. On the other hand the cupric oxide spirals are easity disintegrated. Asbestos plugs have been exclusively used in this laboratory. A forty-five centimeter 1 layer of cupric oxide in the wire form (p. 24) is then introduced and an asbestos plug or a short cupric oxide spiral is placed on top of it. Owing to the weight of the column of cupric oxide the plug or spiral should be supported from beneath by the short plunger described above. A ten centimeter space is then left for the boat in which the substance to be burned is generally placed and the large cupric oxide spiral is inserted in the tube, leaving about two centimeters between the boat and the spiral. The remainder of the tube is unoccupied. Well-fitting, one-holed, red rubber stoppers are in- serted in each end of the tube. The oxygen or air is admitted at the anterior end of the tube, i. e., that con- taining the long cupric oxide spiral, while the prod- ucts of combustion issue from the other or the exit end of the tube. The stopper in the anterior end is generally furnished with a well-fitting glass tube which is connected directly by means of rubber tubing with the purifier. It is highly desirable to use a straight glass stop-cock (Fig. 12, p. 51) in place of the glass tube. Where rubber and a screw pinch-cock are used the cock often cuts the rubber, causing leaks which may mean loss of carbon dioxide and water. The glass stop-cock does away with this difficulty, and 1 A forty centimeter length of cupric oxide will suffice to burn most ma- terials, but a forty-five centimeter length is much safer to use. BOATS 29 furthermore furnishes a length of tubing easily exam- ined for traces of condensed products of distillation or sublimed material which has diffused backwards and escaped oxidation by the cupric oxide spiral. Such condensation rarely occurs, however, if the combustion has been properly conducted. The stopper in the exit end of the tube is connected directly with the water absorbing tube of the absorption apparatus. It is im- portant, therefore, to see that the hole in this cork is of a proper size to take snugly the glass connecting tube of the water absorber. The combustion tube thus prepared is placed in the furnace and is ready for the preliminary " burning out " described on page 45. BOATS The material to be burned, if a solid or a high boil- ing liquid, is almost invariably placed in a porcelain, copper, or platinum boat which is introduced into the combustion tube by means of a long wire with a bend on the end. The boat should preferably have a ring handle or extension to facilitate inserting and with- drawing it. Porcelain. The porcelain boat should be approxi- mately seventy-five millimeters long and not too wide to enter the combustion tube readily. This boat is especially advantageous for beginners as the charring of the material is well seen against the white back- ground. Furthermore, it is seen at a glance by the absence of any black color in the boat when all the carbonaceous residue has been oxidized. 30 ELEMENTARY ORGANIC ANALYSIS Copper. Occasionally substances are met with that are unusually refractory and require either unusual heat or length of time for their complete oxidation. Such materials may often be burned to advantage in a copper boat which has been heated till a coating of oxide has ,been formed. While at a high heat the car- bonaceous residue resists the action of the oxygen alone, it is readily oxidized by the cupric oxide coat- ing of the copper with which it is in contact and the copper thus reduced is again instantly oxidized, there- by acting as a carrier of oxygen. In burning substances with the copper boat care should be taken when heating to prevent frothing, and the boat should be covered with a bit of sheet copper which protects the tube from being spattered. Copper boats may be obtained in the market. Owing to their rapid disintegration by alternate oxidation and reduction, it is better to prepare them as desired, using moderately thick sheet copper. A rectangular piece is cut twenty-one by sixty-eight millimeters and by making two folds lengthwise of the sheet a copper trough of rectangular cross-section with a base seven millimeters wide and sides seven millimeters high is I I obtained (Fig. 6). A pair of flat- Fig. 6. nosed pliers are used to bend up each end and a serviceable boat is easily made. A piece of sheet copper sixty-eight millimeters long and seven ABSORBING AGENTS 31 millimeters wide has a strip five millimeters long bent down at each end. This cover when placed on top of the boat prevents spattering on the glass. Platinum. The expense of a platinum boat is so great as to prohibit its general use. Platinum absorbs gases and hence the use of a boat of this metal in a current of oxygen hastens oxidation as does, in a much greater degree, the use of finely divided platinum in the form of platinized asbestos or platinum sponge. ABSORBING AGENTS The products of combustion issuing from the com- bustion tube, i. e., water and carbon dioxide, are re- tained in some absorbent and weighed. As absorbers of water calcium chloride, concentrated sulphuric acid, phosphorus pentoxide, and, at times, solid potassium hydroxide may be noted. Carbon di- oxide maybe absorbed by strong solutions of potassium or sodium hydroxide, solid potassium hydroxide, soda- lime, 1 and barium hydroxide. Calcium Chloride in the granulated form is obtained in the market and should be sifted to remove all of the finer powder which is liable to be mechanically carried along with the cur- rent of gas. It shtfuld be in granules of from two to three millimeters in diameter. It is well to dry the chloride before use by heating in an evaporating dish over a Bunsen flame, care being taken not to fuse the salt. Fused calcium chlo- ride, unless in small lumps, is not an active dehydrating agent, but the coarser, more granular, and porous form may be used in larger pieces. The chloride should be chemically pure and 'as free from basic compounds as possible. 1 Miilder: Ztschr. anal. Chem., i, 2 ; Dennstedt : "Die Entwicklung der organischen Elementaranalyse," p. 105 ; Benedict and Tower : J. Am. Chem. Soc., 21, 389. 32 ELEMENTARY ORGANIC ANALYSIS Potassium hydroxide in stick form or in concentrated solu- tion is very generally used. The stick contains about twenty- five per cent, of water. A concentrated solution is prepared by dissolving one part of stick potassium hydroxide in two parts of water and cooling the solution. Another method consists of dissolving stick potassium hydroxide in a small amount of water and diluting the cooled solution until its specific gravity is I.27. 1 If impurities in any appreciable quantity are present in the hydroxide the solution should be allowed to stand and the supernatant portion should be de- canted off and preserved for use. Soda-lime when used to absorb carbon dioxide must contain appreciable quantities of moisture; hence, the dry fused soda-lime, sold for use in the determination of nitrogen by the method of Will and Varrentrapp, or for drying gases, is not suited for the absorption of carbon dioxide. A soda-lime that has given excellent satisfaction is quickly and easily prepared as follows : One kilogram of commercial caustic soda, " Greenbank Lye," is treated with 750 cc. of water in an iron kettle, form- ing a strong solution, or more properly a thin paste. While still hot one kilogram of quicklime, coarsely powdered, is rapidly added, stirring constantly with an iron rod or a piece of gas pipe. The lime is slaked by the water of the caustic soda solution and soon the whole mass heats and steams. While in this stage it is advisable to keep the mass stirred and the lumps broken. No outside heat is necessary and as soon as cool the product is coarsely pulverized and placed in wide-mouthed bottles and the corks sealed in with 1 Auchy (J. Am. Chem. Soc., 20, 245) prefers a sp. gr. of 1.40. ABSORBING APPARATUS 33 paraffin or wax. When cool it should not be moist enough to show water as such, i.