IAYDCSTRIBLA S D E,VGIIYEERISG CHE.IIISTRY
Februarv. 1926
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A Portable Combustion Apparatus for Detection and Measurement of Small Quantities of Petroleum Vapor' By C. A. Neusbaum, P. L. DeVerter, and E. W. Dean STAIVDARD
OIL C O M P A N Y (NEWJBRSEY), STAXDARD INSPECTIOX I,ABORATORY,
S E of the frcxquent technical problems involved in the
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NEW
YORK, N. Y.
Failure of Older Methods to Satisfy These Requirements
operation of oil-tank vessels is the testing of the atmosphere of tanks and compartments when a ship is to The best method previously available consists in collecting be sent to dry-dock for repairs. There are various methods an adequate set of samples, making a careful physical inof doing this, but tione of them have been found entirely spection at the same time, arid analyzing these samples in satisfactory by the authors. As a result of experience in the Haldane apparatus." inspecting ships of the tank fleet of this company, apparaThe Haldane apparatus is accurate and reliable, but a t tus and procedure have been developed which seem to best the analysis of the samples consumes much time and meet all the requirements of this work. They are proba- it is necessary to take the samples from the ship to the laboratory, frequently a conbly applicable, also, to the siderable distance. In spite testing of oil tanks other of these defects it was bethan those of ships, but the An outline of the relative merits of various types lieved that the importance authors hare confined their of apparatus used for detecting and estimating small of the work warranted emdiscussion to marine probpercentages of petroleum vapor follows a brief disployment of this method lems because their expericussion of the requirements of the work of inspecting until apparatus was devised ence has been entirely in ship tanks. that made greater speed this field. A convenient and accurate portable apparatus which possible without sacrifice of reduces these disadvantages to a minimum, and which General Requirements of accuracy. Ship Tank Inspection* has been developed and used by the authors, is deOther types of nonportascribed. ble apparatus are available, I t seems desirable first to some requiring less skilful point out one or two fundamanipulation than the Halmental principles that apparently are not universally recognized. The first is that no dane apparatus, but none are appreciably more rapid than inspector can write a real certificate of safet'y unless he has the latter when it is used according to an abbreviated prohimself entered the tank or compartment in question and ex- cedure involving simple determination of the contraction amined it carefully for deposits of oil or sediment that may after combustion. The Burrell methane detector has been employed for the generate vapor. Without such an examination the analysis of the atmosphere means nothing more than that the tank determination of small quantities of petroleum vapor, is safe for a man t o ent,er a t the time of testing. The prac- and under favorable conditions might prove satisfactory. tice of taking samples by lowering a sampling tube into the An attempt was made to use this apparatus, but it was not suitable under the conditions encountered. The temperacontainer seems entirely inadequate. Another important principle is that the maximum per- tures of oil tanks just after they have been steamed and missible content of petroleum vapor is fixed by its effect on cleaned are decidedly irregular, and to give accurate results men inhaling the atmosphere rather than by the lower the Burrell detector must be approximately in thermal equilimit of the explosi.ve range. The lower explosive limit librium with the atmosphere in which it is used. The time varies with different' hydrocarbons, but 2 per cent is, per- consumed in reaching temperature equilibrium in each tank haps, a representative figure. On the other hand. it is stated3 of a ship is prohibitive. It has recently been proposed t o use the Koehler safety that petroleum vapors, in concentrations of 0.3 per cent or more, are intoxicating to some people on exposure for lamps as an indicator of the presence of combustible con30 minutes or longer: so the actual danger limit' is far below stituents in the atmosphere of tanks. This lamp shows an the explosive limit. The authors have found that men increase in flame height when it burns in an atmosphere were able to work in tanks for periods consideratdy in excess containing combustible gases or vapors but it is not conof 30 minutes when a maximum of 0.2 per cent of petroleum sidered to be reliable in indicating concentrations lower han rapor, figured as pentane, was enforced as a limit, and have 0.5 per cent. Its use is undoubtedly preferable to the oldfashioned scheme of relying on odor as an index of content adopted this figure for their inspection work. The third fundamental is a practical one. The working of combustible gas; but it hardly seems justifiable to rely time of a ship is very valuable and any delays in her movement on it for testing tanks prior to turning them over to workmen cause the loss of considerable sums of money. It, is therefore with the guarantee that they are safe for work with flames, desirable to make an inspection rapidly and t o have the hot rivets, etc. results available for sending to the master in the shortest The N-D Portable Apparatus possible time. The authors' experience therefore indicated that the most 1 Received September 18, 1925. 2 The Marine Department of the Standard Oil Company (New Jersey) practical apparatus would be one which represented a com-
has issued a pamphlet covering its rules and regulations for this work. A limited supply of copies are available which will be furnished 0x1 application t o men or organizations interested in work of this nature. 3 Jones and Yant, Bur. M i n e s , Tech. P a p e r 362, 8 (1924).
4 Jones, Bur. .Mines, Repl. 299-B-71; Burrell and Seibert, I h i d . , Bull. 42 (1913). 6 Wilson and Wilkm, TIUS JOURNAL, 16, 115% (1924).
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promise between the accuracy and reliability of the Haldane, and the portability of the Burrell detector. Their apparatus, which for purposes of convenient reference has been designated as the “N-D” apparatus, is really a laboratory set, which, however, can be readily transported to a convenient location, such as the cabin of a ship that is to be inspected. It requires careful handling and its operation involves a fair amount of skill and training, but it has served a very useful purpose in making accurate results available in the shortest possible time after a ship is ready for inspection. Combustion System
Vol. 18, No. 2
the wire may be brought to the same temperature by reference to the ammeter reading rather than by observation of the wire itself, which is frequently made difficult by the cloudiness of the walls of the chamber. Source of Electric Current
The electric current for heating the platinum wire is supplied by three dry cells or three small two-cell Edison storage batteries. Dry cells have been found most convenient for ship inspection in that new ones can always be supplied from the vessel stores.
Procedure for Analysis A detailed drawing of the apparatus is shown in Figure 1. It consists of a slow combustion chamber, b, and buret The U-tube, which has previously been filled with mercury or measuring tube, f, combined in the form of a U-tube. until the level in the buret is at 0, is connected with sample tube, d, and the stopcock turned so as to put the combustion
d
b,
chamber into communication with the atmosphere. The rubber bulb, a, is pressed to force the mercury up to the bottom of the stopcock, which is turned through one-quarter turn so as to hold the mercury. The stopcock is gradually turned making communication between the chamber and sample tube, d, at the same time allowing the sample to be drawn in as the mercury seeks its level. This sample is used to clean out the connecting tube, i, and the combustion chamber, b, by turning the stopcock so as to make communication between the atmosphere and the chamber and pressing the bulb until the mercury level rises to the bottom of the stopcock. A sample is then drawn from the sample tube, d. After the sample has been drawn the stopcock is opened to the atmosphere to allow the pressure to equalise. The
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Figure 1-N-D
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12% INCHES Portable Combustion Apparatus
The ground-joint stopper used in the combustion chamber is held in place by two rubber bands which are stretched over the lugs shown in the figure. The reason for using a ground-glass connection is twofold: (1) The small platinum wire, which may burn out, can be renewed easily and the chamber cleaned by removing the stopper. (2) I n case of an explosive mixture or the development of excess pressure, the rubber bands stretch, allowing the stopper to rise, SO that the gaseous mixture can escape. This usually prevents breakage of the apparatus. Mounted on the buret or measuring tube is a scale graduated in millimeters. The use of this scale will be discussed under the section on calibration. The U-tube is supported by two hard-rubber disks and is immersed in water to insure a constant temperature. Rheostat
The nichrome wire rheostat, T, is used to give a more careful regulation of the temperature of the platinum coil than can be obtained by the batteries alone. An air sample containing a large amount of combustible vapor causes the wire to become very hot, and unless some additional resistance is thrown into the circuit, the wire may be burned out. Ammeter
The ammeter, m, is inserted in the circuit and its reading noted when the desired bright yellow color of the platinum wire, q, is observed. Thereafter by adjusting the rheostat
Figure 2-Characteristic Curve for N-D Portable Combustion Apparatus, Baaed on Pentane
stopcock is closed completely, the reading noted, and, with all the resistance thrown in, the switch, 2, closed. The resistance is then regulated until the desired reading of the ammeter is obtained. After burning for 2 minutes the cur-
February, 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
rent is broken and the sample allowed to cool for 3 minutes. After cooling, the contraction in millimeters, indicated on the scale, is read. PRECAUTIONS-The walls of the buret and combustion chamber should be kept slightly moistened to insure accurate results. Water should be kept above the point at which the platinum wires are sealed into the glass stopper, since any leaks around the stopper or seals can be detected readily. Calibration of Apparatus
The results obtained by use of the apparatus are empirical and their interpretation involves the use of a calibration table or chart. The fundamental factors involved in working u p such a table or chart are ably and fully discussed
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by Jones and The chart employed in the present work is similar to those described by Jones and Yant. The method of calibrating the N-D apparatus has been to prepare mixtures of air with varying proportions of hydrocarbon vapor, and to determine the composition of these mixtures with the Haldane set, figuring the percentages of combustible material on the basis of the chemical equation characteristic of pentane. Portions of the same mixtures were tested in the N-D apparatus and the contractions (in millimeters) determined, which were equivalent to the various percentages of hydrocarbon vapor, calculated as pentane. These figures are used in preparing a chart such as is shown in Figure 2. This chart is used to convert the contraction readings into percentages of combustible vapor.
Another Important Role Played b y Enzymes in Bating’ By John Arthur Wilson and Henry B. Merrill A. F. GALLUN& SONS Co.,MILWAUKEE. Wis.
During the liming of skin for tanning, keratin is thus rendering the N M O D E R N tannery partially broken down into keratose, which is soluble grain surface of the finished practice, after the skins in neutral or alkaline solution, but is precipitated at l e a t h e r finer, softer, and have been l i m e d , u n its isoelectric point, pH = 4.1. If this material is c l e a r e r in color, although haired, scudded, and washed, left in the skin and precipitated there by the acid tan Rohm and Haas’ have sugbut before they are tanned, liquors, the value of the finished leather is lowered. gested that probably a more they are subjected to a procIn bating, keratose is broken down by the enzymes important function consists ess called bating, which conto a point where it is no longer precipitable by acid. in dissolving out any remains sists in paddling tJhe skins, The rate of digestion of keratose is directly proportional of u n o r g a n i z e d material still plumped by the alkaline to the concentration of enzyme and is a maximum at known as scud, which is delime liauor, in a warm soluPH = 7.9. r i v e d f r o m t h e epithelial tion ofpancreatin and buffer tissues and is insoluble in salts designed to keep the pH value a t about 8 until they have been reduced from a neutral or alkaline solution. Wilson and Daub demonstrated conclusively by means of plump to a flaccid condition.2 Bating is an extremely complex process and one which is difficult to operate efficiently photomicrographs that the elastin fibers of calfskin can be at all times. Limed skin, with its manifold and variable pro- completely removed by solutions of pancreatin without tein degradation products, may be acted upon by enzyme appreciable damage to the collagen fibers. I n fact, the only bate liquors, with their countless bacteria, in many different action of the enzymes in bating which they could detect ways. Depending upon the kind of skin, its previous treat- under the microscope was the removal of the elastin fibers. ment, and the kind of leather desired, bating may serve one However, the writers’ experience since that time has demonor more very useful purposes, or it may be without appreci- strated clearly that the beneficial effects of the enzymes in able effect, or i t may actually prove harmful. Moreover, bating are not always measured by their power to digest where bating is desirable, the method of operation must elastin. If the dissolved keratose which is present in limed be varied to correspond with any variations in previous skin is not removed before tanning, it will be precipitated treatment of the skin. in the skin by the acid tan liquors, with consequent damage It has been the aim of the writers to ascert:tin all of the to the appearance of the grain surface of the leather. The useful purposes which bating may serve, to study the mechan- soluble keratose is much more quickly broken down by the ism of the reactions involved, and to devise means for con- enzymes of the bate liquor than the insoluble elastin fibers, trolling each reaction so that the particular purpose may be and it was found in numerous tests that nearly all measurable served most efficiently. Already five different purposes effects of the bating of certain types of calfskin were obtained of bating have been recognized and means for their quanti- before the elastin fibers had been measurably attacked. tative control indicated: (1) rendering the skin flaccid; Thus the removal of keratose must be added to the list of ( 2 ) adjusting the hydrogen-ion concentration of‘ the solution important functions of bating, and the following report deals adhering to the skin; (3) removal of lime; (4) removal of with the quantitative relations involved and with the measelastin fibers; and ( 5 ) partial digestion of collagen. To urement of the keratose digesting power of bating materials. these the writers are now adding a sixth, the removal of Preparation of Keratose keratose, and this forms the subject matter of the present The material in which we are interested consists of those paper. decomposition products of keratin which are soluble in alThe prevailing opinion has been that the chief function Rosenthal, J . A m . Leather Chem. Assoc., 11, 463 (191ti). of the enzymes in bating is to digest the elastin fibers of the
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Krall, Socidt~Anonyme anc. B. Siegfried, private bulletin, 1918. Seymour-Jones, J . Sac. Leather Trades’ Chem., 4, 60 (1920). e Wilson and Daub, THISJOURNAL, 13, 1137 (1921). 4
Received October 15, 1925. 2 For a detailed account of this process see Wilson, “The Chemistry of Leather Manufacture,” p. 173.
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J . A m . Leather Chem. Assoc., 18, 516 (1923).
