THE ANALYST’. JANUARY, 1902. THE DETERMINATION OF CARBON I N STEEL BY DIRECT COMBUSTION. BY BERTRAM BLOUNT, F.I.C. (Read at the Meeting, November 6, 1901.) IN the ANALYST for June, 1900, I have discussed the question of devising a practicable method for the determination of carbon in steel by direct combustion--i.e., without having recourse to the usual process of previously removing the iron by solution in potassium cupric chloride or the like solvent. I would lay emphasis on the adjective There are many prescriptions for burning steel and collecting the carbon dioxide representing its carbon, but they hardly satisfy the condition of being workable. Either the metal has to be finely divided by mechanical means or the iron must be removed by volatilization in a current of chlorine or bromine without attacking the carbon, which is only possible if air and moisture be completely excluded-a condition difficult of attainment. Such operations fall far short in simplicity and accuracy of a method which shall be capable of oxidizing steel directly practicable.”THE ANALYST’.JANUARY, 1902. THE DETERMINATION OF CARBON I N STEEL BY DIRECT COMBUSTION. BY BERTRAM BLOUNT, F.I.C. (Read at the Meeting, November 6, 1901.) IN the ANALYST for June, 1900, I have discussed the question of devising a practicable method for the determination of carbon in steel by direct combustion--i.e., without having recourse to the usual process of previously removing the iron by solution in potassium cupric chloride or the like solvent. I would lay emphasis on the adjective There are many prescriptions for burning steel and collecting the carbon dioxide representing its carbon, but they hardly satisfy the condition of being workable.Either the metal has to be finely divided by mechanical means or the iron must be removed by volatilization in a current of chlorine or bromine without attacking the carbon, which is only possible if air and moisture be completely excluded-a condition difficult of attainment. Such operations fall far short in simplicity and accuracy of a method which shall be capable of oxidizing steel directly practicable.”2 THE ANALYST. and completely in substantial fragments, such as drillings or turnings, and of yielding the whole of its carbon as carbon dioxide free from other gases absorbable by potash. In the paper already referred to, and in another on the determination of oxygen in commercial copper (ANALYST, xxi., 57), I have pointed out that it is unnecessary for the chemist in performing analytical operations of this class to restrict himself to the use of temperatures commonly attained in the combustion furnace.With proper precautions a temperature of 1,100" C. is as manageable as is one of 800" C., and reactions which are slow and imperfect at the latter take place smoothly and corn- pletely at the former. Such difficulties as have to be overcome arise from the fact that ordinary apparatus and appliances are not as a rule designed for the production and utilization of these higher temperatures, and certain modifications in instruments and procedure are called for.In my previous experiments I endeavoured to burn steel turnings in oxygen without admixture of any oxidizing or fluxing agent. I found that there was a, considerable tendency to leave a core of unburnt metal which was usually free from carbon, but, if occurring, raised a doubt whether the combustion was complete; if heating was continued until this core was oxidized, the operation was unduly pro- longed, and errors inseparable from a lengthy combustion crept in. I n spite of these obstacles, the results obtained were sufficiently encouraging to warrant further study of the subject, and I turned my attention to the use of some suitable oxidant. Of all the oxidizing materials which suggested themselves, lead chromate appeared preferable, because, unlike lead oxide (no doubt an ideal carrier and flux for the purpose in hand), it does not attack porcelain violently, and, further, when tempo- rarily reduced, as it may be by the steel even in an atmosphere of oxygen, it does not yield fluid masses of metallic lead, and consequently does not imperil the integrity of platinum. Therefore two standard refractory materials become available, Using lead chromate, the process resolved itself into this : A weighed quantity of the steel, usually 5 grammes, in the form of drillings or turnings, often of relatively stout section, was mixed with 15 to 20 grammes of lead chromate which had been recently fused and thus freed from oxidizable impurities.The mixture was put into a large porcelain boat, the boat was placed in a long, deep tray of platinum sheet, and the whole slid into a porcelain tube.The object of the platinum tray was to prevent any chromate which might creep from coming in contact with the porcelain tube. It was found impracticable to use a platinum boat, as the hard fused mass of chromate and oxide of iron left after combus,tion was difficult to remove without injuring the boat. The front part of the porcelain tube contained copper oxide, and was heated in a Fletcher combustion furnace. The back part was similarly heated, but the precise spot where the boat lay was raised to a temperature considerably higher than could be reached by the combustion furnace. After many trials of different burners, a benzoline blast-lamp was found to be fairly effective for this purpose.I may remark in passing that there is an opening for a burner as handy as a common bunsen, but giving the temperatures usually requiring a blast for their production-ie., ranging from the melting-point of copper to that of cast iron. I have not yet been able to procure a burner of this description from chemical dealers, and in many operations am compelled to have recourse to a mechanical blower, when a self-contained blast-THE ANALYST. 3 lamp of ample power wcjuld be preferable in every way. An electrical method of heating may be the best solution, but there is nothing of the kind in common use except little muffles for dental work, and I have not had time to design such an apparatus for my special needs. The arrangement of the whole apparatus is shown in the accompanying diagram (Fig.1). Starting on the left, we have a potash bulb and a U-tube of soda-lime to purify the oxygen, and afterwards the air used for sweeping out the tube. The glass T-piece with free flattened end allows the boat to be seen in the tube during combustion. A Fletcher combustion furnace is used, supplemented by a beneoline blast-lamp at the point where the boat is placed. Connection at the far end of the porcelain tube is made by a glass cap on a rubber ring instead of the usual cork. This cap is drawn down so as to St small tubing for connection with the absorbing train. The first potash bulb is empty, and serves merely for cooling. It can, if necessary, be FIG. 2. FIG. 3. immersed in a beaker of water. A U-tube of sulphuric acid on pumice dries the gas, and a potash bulb and similar U-tube constitute the weighed absorption apparatus.A second weighed sulphuric acid U-tube serves as a check on the efficiency of the first. It is weighed every three or four combustions, and should gain only fractions of a, milligramme. A guard tube of sulphuric acid on pumice completes the train, and to this the pump can be attached. The U-tubes are designed so that the gas is compelled, not merely to traverse two columns of pumice, but to bubble through the acid. The bottom bulb forms a useful store of acid with which the pumice can be refreshed, for it often happens that when sulphuric acid on pumice alone is used, the acid on the surface of each piece may be diluted and exhausted, although there is still plenty of strong acid in the centre of each piece of pumice. The tube will then cease to act efficiently, but if it contains a store of acid actually fluid, this can be washed over the pumice in each limb, and replace the used-up acid.The potash bulb designed by my chief assistant, Mr. S. Dickson, is also novel, and an improvement on the ordinary forms. A diagrammatic sketch is given A diagram of the tube is shown (Fig. 2).4 THE ANALYST. (Fig. 3). The pctash bulb differs from most apparatus of the kind by being asymmetrical. The entrance limb is larger and heavier, and the bulb hangs natur- ally in its proper position for absorption, so that no tying up or tilting is necessary. An extra passage through the liquid is secured by an internal tube in the first bulb, and both entrance and exit tubes project a little way into their respective bulbs, and are turned aside from the centre, their ends being also contracted.Under reasonable conditions of use splashing is almost impossible. I use these bulbs for all absorption work, and find them preferable to any other design with which I am acquainted. When the method was carried out in this manner, satisfactory results were obtained. The high temperature employed made it necessary to insure that the drying tubes were kept in excellent condition, and were not run too long without renewal.* It was also requisite to have a good length of tube projecting beyond the furnace, to avoid over-heating the rubber connections. A porcelain tube 26 inches by l g inches was found convenient.With an adequate temperature and time of heating (about one hour), no difficulty was experienced in burning the whole of the steel ; even thick turnings were oxidized, and left no core. In the earlier experiments, in which the conditions were less thoroughly understood, discrepancies occur between the standard method by solution and combustion and the method of direct combustion. In the later experiments these differences tend to disappear. The figures obtained are given below : Tyre steel ... Rail steel ... Rail steel ... Nickel steel Solution Method. Carbon per cent. ... ... 0.675 ... ... 0-404 I . . ... 0.399 ... ... 0-378 ... ... 0.643 ... ... 0.618 ... ... 0.401 ... ._. 0.432 ... ... 0,430 ... ... 0.457 ... .:. 0.470 ... ... 0.323 Direct Combustion. Carbon per cent.0.619 0.393 0.407 0.330 0-645 0.557 0.419 0.435 0.408 (2) 0.393 (3) 0.438 0-429 (1) 0.324 (2) 0.324 (1) 0.422 ... ... ... ... ... ... ... ... Tyre steel 0.459 Structural steel (plate) 0.288 Rail steel 0.455 ..- 9 , 9 , - - * I t is evident from these results that the method is reliable when properly handled. But it still has several defects, due chiefly to the imperfectly refractory nature of the materials at one's command. At the temperature necessary the glaze of royal Berlin porcelain is slightly sticky, and the platinum tray adheres thereto. * The eficiency of the train of absorption tubes finally adopted was tested by numerous blank experi- ments, and by the use of a second dfying tube after the potash bulb weig9d independently of the drying tube proper.THE ANALYST.5 I t is diflicult to detach, and when forcibly removed is itself often deformed and injured, and removes fragments of the glaze, frequently leading to the breakage of the tube. The porcelain boat also adheres to the platinum tray, and sometimes can hardly be withdrawn from the tube without tearing the platinum, which is itself stuck t o the porcelain tube. Various devices suggest themselves to remedy these inconveniences, and these I propose to examine when work allows. In the mean- time, I am of opinion that the method will suffice to check the results obtained by the usual process in the event of a doubt arising. So much has the customary process been elaborated that there are schools of analysts who quarrel about the position of a potash bulb, and seek to standardize every piece of apparatus.All this is, of course, mischievous and absurd, and it is well to remember that the real object in view is to determine accurately the percentage of carbon irrespective of any particular procedure. Hence a process which has not yet suffered from pseudo- standardization presents some advantages. DISCUSSION. Mr. RAYMOND Ross inquired whether it would be possible ‘to use a piece of glass tube for each experiment instead of a permanent porcelain tube with boat and platinum shield. He had himself obtained very satisfactory results in carrying out with certain organic substances some combustion experiments, in which he had been obliged to use a very short furnace, by employing lead chromate alone as an oxidizing agent and conducting the combustion in a piece of glass tube about 10 or 12 inches long. Mr.ARCHBUTT said that Mr. Blount was to be congratulated upon having, after long perseverance, at last found a method of burning steel perfectly without going through the roundabout process of decomposing with copper salts, and then burning and weighing the carbon so separated. Of course, it was to be hoped that Mr. Blount would be able ultimately so to improve the process that it would be sufficiently rapid to replace the ordinary more cumbrous method. At present it would hardly do that, for in the ordinary process a number of samples of steel would be dissolved at the same time in the double chloride of copper and potassium, and the carbonaceous residues filtered off one after another; and, as the combustion took place fairly quickly and at a comparatively low temperature, a considerable number of deter- minations could be carried out in one apparatus in a single day.The new method, however, as he had remarked on a previous occasion, was valuable in ite present stage because it afforded a complete check upon the results of the ordinary process. Mr. Blount, in referring to the use of lead chromate, had used the text-book expres- sion ‘( recently fused.” Surely, however, it was immaterial whether the fusion had taken place recently or not, provided that the lead chromate really had been fused and had been so kept that it could not absorb moisture or carbonaceous matter. In the course of some experiments in standardizing a, pyrometer for obtaining the cooling curves of metals, he had found it possible witb a small furnace, by using compressed air at about 70 pounds per square inch and coal gas.under a pressure of 6 or 7 inches of water, to obtain temperatures very much higher than with gas at ordinary pressure and air supplied from a blower. He had easily melted copper in6 THE ANALYST. this way. Another suggestion was that a certain proportion of oxygen might be mixed with the air from the blower, by which a higher temperature would be obtained without increase of pressure. He would like to hear at what rate the oxygen was passed over the burning steel, because, from what was said about the high temperature of the gas that had to be dried, it would seem that the oxygen must be passed through at a very rapid rate. At a moderate rate-say &om four to six bubbles per second-the gas might be expected to become sufficiently cool by radiation very soon after escaping from the combustion tube.If the rate were more rapid, possibly soda-lime might be a better absorbent than caustic potash for the carbonic acid. He had at one time experienced some difficulty in the absorption of the carbonic acid by potash and the weighing of the potash bulbs. His oustom was not to aspirate air through the combustion furnace after burning the carbon, but first of all to pass oxygen through the apparatus and weigh the bulbs full of oxygen at intervals of ten minutes until constant, then burning the carbon and weighing the bulbs again full of oxygen at similar intervals till constant.He had found, however, that the bulbs showed a tendency to lose a few tenths of a milligramme continuously, which was ultimately traced to the not quite sufficiently hygroscopic character of the drying tube ah the end. In that tube had been used, not calcium chloride-a very imperfect drying agent-but broken-up pieces of ordinary stick-potash, which was very commonly used for the purpose. Dittmar, however, in his researches on the combining proportions of oxygen and hydrogen, had demonstrated the remarkable drying powers of potash, which had been freshly fused until it contained no water. So-called pure potash, when heated in a platinum or a nickel dish, lost from 15 to 20 per cent. of water, and became perfectly anhydrous ; and if this, after cooling, were broken into small pieces and used for filling the small tube at the end, no loss occurred in the potash bulbs within ten minutes or a quarter of an hour, and they could be got almost absolutely constant.He thought that if Mr. Blount were to give up aspirating air through the apparatus, and weigh the bulbs full of oxygen instead, the results would be obtained perhaps a little more quickly. Dr. DYER inquired whether the use of sulphuric acid for drying purposes was wholly desirable in view of the fact, which had been pointed out by Mr. 911en in the course of the discussion on Mr. Blount’s previous paper on the same subject, that sulphuric acid was liable to absorb small quantities of carbonic acid. Mr. BLOUNT said he was afraid it would not be possible to use a glass tube as suggested by Mr.ROSS, because the essence of the process was the high temperature employed. The temperature necessary was so considerable that the glass would blow out with the ordinary pressure needed to drive the oxygen through the train of apparatus. Even when chromate of lead was used, the temperature requisite in order completely to burn steel which was in stout fragments was such that the use of glass, however hard, was impracticable. He acknowledged freely that at present he had no intention of putting this method forward as capable of replacing the ordinary process. He was alive to the necessity of speed, and the method might not compete in effective speed with the older process; it was true that its real speed was greater, because, although the combustion took longer, there was no necessity for dissolving and filtering.He thought he might claim for it that it could beTHE ANALYST. 7 employed instead of the old process in any case of difficulty or doubt as to the purity of the reagents used, or when it was desired to fall back upon a totally different method, which should not involve any single step at all comparable with those of the ordinary process. He agreed with Mr. Archbutt’s comment as to the term ‘‘ recently fused,” and, in fact, had erased it once, but, the search for a more suitable expression having been unsuccessful, he had replaced it. Clearly it was merely essential that the lead chromate should be kept clean after fusion, though it was perhaps better practice that the fusion should be recent, so as to minimize any chance of dirt being present, and that was the only excuse for the term.He had tried the. use of what was known as ‘( press gas,” which, at a pressure of a few inches, was no doubt comparable with the pressures mentioned by Mr. Archbutt ; then moderate pressure was hardly enough, but if gas under a pressure of a few pounds were available, it would probably not be necessary to use a benzoline blast- lamp. There was no difficulty in absorbing the carbonic acid when the oxygen was passed through at any reasonable rate. The trouble arose in absorbing the water. The use of fused potash might well be of assistance in this connection. Mr. ARCHBUTT inquired where all the water came from. Mr. BLOUNT said that a tangible quantity would come from the tube and apparatus, which could never be got completely dry, and in any case fre- quently had to stand overnight. Then, again, the copper oxide was somewhat hygroscopic, and there were a number of other sources of water which had to be reckoned with. He had never had occasion to try whether carbonic acid was absorbed by sulphuric acid, but that matter did not really bear upon the present case, because, although there might be some absorption if concentrated carbonic acid were passed over sulphuric acid, there would be none in the case of a gas containing but a small percentage of carbonic acid ; one had to consider the partial pressure of the gas. These attenuated gases could be passed through even water without any appreciable loss of carbonic acid. ARSENIC COMMITTEE. The joint committee of the Society of Chemical Industry and of the Society of Public Analysts has now completed its investigations, and the report will be presented to the respective Societies in January.