ISSN:0003-2654    

DOI:10.1039/AN94873FX045

出版商:RSC    

年代:1948

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN94873BX047

出版商:RSC    

年代:1948

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN94873FP071

出版商:RSC    

年代:1948

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN94873BP075

出版商:RSC    

年代:1948

数据来源: RSC

摘要:

426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively.Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction

ISSN:0003-2654    

DOI:10.1039/AN9487300643

出版商:RSC    

年代:1948

数据来源: RSC

摘要:

644 [Vol. 73 The Determination of Radioactive and Stable Tracer Isotopes The following five papers were read at a meeting of the Physical Methods Group at Birmingham on April 2nd 1948 The Measurement of Beta-Activity BY A. G. MADDOCK THE chemist who uses tracers is interested especially in three aspects of the measurement of p-activity (i) the attainment of the greatest accuracy in the shortest time (ii) the measure-ment of the softest or least energetic p-particles and (iii) the development of the greatest sensitivity in the determination of specific activity. Present methods with due precautions will allow an accuracy to within about 1 to 2 per cent. on most determinations of relative activity. An accuracy to within 06 per cent. or better has seldom been achieved.Absolute measurements of activity are generally liable to much greater errors; quite recently results differing by nearly an order of magnitude have been reported for a single source by different laboratories. However as Dr. Whitmore will show in his paper coincidence methods provide a technique capable of yielding accurate measurements of absolute activity. In recent years three devices for measuring /3-activity have found general use. (i) Ionisa-tion chambers with electroscopes or electrometer tube amplifiers as the measuring device. (ii) Electron multiplier tubes feeding electronic counting devices commonly called scalers or counting rate meters. The multiplier tube may be activated either directly by the /3-particles or by the photons ejected from a naphthalene filter interposed between the source and the first electrode of the multiplier tube.(iii) Geiger - Muller tubes of either the self-quenching or the non-self quenching variety operating scalers or counting rate meters. The last mentioned arrangement at present is about five times as sensitive as the previous methods and is therefore most suitable for the chemist concerned with tracers.* The self-quenching type of Geiger - Miiller tube which is most commonly used to-day, consists of a cylindrical ionisation chamber the central collecting electrode being a stiff wire of about 10 mil diameter. It is filled with a mixture of a vapour of polyatomic molecules with a rare gas. Argon under 9 cm. mercury pressure with ethyl alcohol vapour under 1 cm. mercury pressure is a commonly used mixture.The vapour quenches the discharge preventing its propagation by photons or secondary electrons by absorption followed by dissociation of the molecule. The general behaviour of these tubes has been explained in a qualitative way by C. G. Montgomery and D. D. Montgomery,l H. G. Stever,2 S. A. Korff and R. D. Pre~ent.~ Desirable features in a counter are (i) long flat plateau (ii) low starting potential and (iii) high efficiency. Examination of the frequency of pulses separated by various small time intervals shows that the slope of the plateau is largely due to multiple pulses-one or more spurious pulses following closely on the primary pulse. The proportion of such spurious pulses and thus the * The vibration electrometer and ionisation chamber described by Palersky Swank and Greenshik shows promise of nearly equal sensitivity to and greater reliability than the Geiger - Miiller tube set December 19481 MADDOCK THE MEASUREMENT .OF BETA-ACTIVITY 646 slope of the plateau depends both on the shape of the tube and its filling.A spurious pulse will occur for example if an activated quenching vapour molecule radiates before dissociating near the cathode of the tube. A physical-chemical investigation of the mechanism of the Geiger - Muller tube would be most profitable and interesting. The slope of the plateau of agood Geiger - Muller tube should be not more than 0.05 per cent. per volt. It should be noted that this implies the high-voltage supply to the tube being stabilised to within 0.1 per cent. for 0.5 per cent.accuracy. Even if the high-voltage supply is suitably stabilised another imperfectly understood factor complicates the measurement. It has been found that the counting rate at a given position on the plateau depends on the room temperature. At one time this was attributed to condensation of the polyatomic vapour s 2 0 0 @ " I Z .M. TUBE CHARACTERISTIC __ POTENTIAL APPLIED. VOLTS Fig. 1 - o f t e n ethyl alcohol-on the wax ebonite etc. used in the construction of the tube. Alter-natively adsorption effects were assumed at higher temperatures. However the effect is observed even with all-metal and glass tubes. This behaviour suggests a change in the efficiency of the counter and therefore of the specific ionisation of p-particles within the sensitive volume of the counter.It is difficult to see how such a change can occur in a closed metal and glass counter with a helium - methane filling. Further the magnitude of the effect appears to depend to some extent on the shape of the counter. It has been shown by the Atomic Energy Research Establishment that the effect is connected with the spurious pulse rate and might therefore be connected with changes in the dissociation probability of the activated quenching molecule with the temperature. Two ways of avoiding this inaccuracy without attempting to thermostat the counter, have been used. The older method is to bracket measurements of the activity of an unknown sample with determinations of the background and of the activity of an arbitrary standard. The latter is usually a small sample of a uranium compound mounted in varnish to prevent accidental spilling.The activity of the sample is then corrected for changes in the efficiency of the counter as measured by the change in the activity of the standard. An uncertainty is introduced by our present ignorance whether a change in temperature equally modifies the efficiency of the counter for all P-ray energies. Thus it might prove necessary for the standard to emit the same P-ray spectrum as the sample measured. A second method reduces the temperature effect by eliminating the spurious pulses. A circuit is used whereby the primary pulse produced in the Geiger - Muller tube by the P-ray initiates a square pulse which is applied to the anode of the counter and is of sufficient size to reduce its potential below th 646 MADDOCK THE MEASUREMENT OF BETA-ACTIVITY [Vol.73 starting potential. Such a circuit is similar to the multi-vibrator quenching circuit used by Getting5 with non-selfquenching tubes. The length of the quenching pulse generally deter-mines the response time of the counting unit. The use of this circuit generally improves the plateau of the counter and reduces its susceptibility to temperature effects but also reduces the counting rate at which coincidence corrections become necessary. It is however, generally convenient to have the response time and thus the coincidence correction determined by a known time constant. To increase sensitivity it is necessary to reduce the background counting rate as the statistical error depends on the square root of the total count.The background of an unscreened counter can be considerably reduced by surrounding it with a lead box or “castle.” The castle absorbs radiation from nearby radioactive materials including the radioactive content of the laboratory building itself and the softer components of the cosmic radiation. Brass bell-jar counters with mica windows of about 1 to 2 cm. cross section in a castle with 1.5-inch lead walls generally possess a background of about 6 to 8 counts per minute. Although the cosmic ray contribution to the background may be further reduced by a very much increased thickness of lead shielding intermediate thicknesses might increase the background by shower production. No data seem to be available on the optimum thickness of lead for this application.In clean laboratories cosmic ray effects contribute about 60 per cent. of the background. The remaining 40 per cent. is due to radioactive contamination of the Geiger - Muller tube and surroundings. In this connection it is preferable to use lead smelted more than 50 years ago in the construction of the castle in order to avoid contamination by Radium D. After due allowance for the difference in range between a- and 13-particles the a-background of an iopisation chamber of equivalent size to a bell-jar type Geiger - Muller counter is much less than might be expected in view of the known relation of a- to /?-active products in the naturally radioactive series. It is therefore possible that part of the contamination contribution to the background is due to the lighter naturally /%active bodies especially potassium.By the use of a pair of counters mounted vertically one above the other the cosmic ray background may be largely eliminated. Only the lower counter possesses a window below which the sample is placed. The counters are arranged to feed an anti-coincidence circuit arranged so that pulses occurring in the lower counter and not in the upper are recorded. The majority of the cosmic rays travel vertically and will cause simultaneous pulses in each counter; the above arrangement prevents such pulses from contributing to the background. Thus the effect of the vertical component of the cosmic rays is eliminated. Since the statistical error on a measurement is inversely proportional to the square root of the total count if the counting time is constant the accuracy of the measurement of the activity of a material can only be increased by raising the counting rate of the sample used.Since the specific activity of the material is assumed constant the counting rate can be increased only by enlarging the effective area of the sample which means increasing .the area of the counter window. For bell-jar counters the cosmic ray contribution to the background is roughly proportional to the cross sectional area of the counter; the contamination contribu-tion is presumably proportional to the surface area of the counter and therefore also depends on the cross section of the counter. The area of the window of the counter may be taken as equal to its cross-sectional area.Thus increase in the window area of a counter leads to increased accuracy of measurement of specific activity although the background increases at the same rate as the activity due to the sample. It is of course assumed in this argument that an ample supply of the material of unknown activity is available. Electrical limitations on the size of large Geiger - Muller tubes do not appear to have been studied but a number of tubes with windows of area up to 20 cm? have been found satisfactory. With larger windows the starting potential and the dead time of the counter increase considerably. The problem of detecting the longer-lived /?-active isotopes is largely one of the measure-ment of soft /3-particles. Commercially-produced bell-jar type Geiger - Muller tubes available in this country may be obtained with windows of 20 and 6 mg./cm.2 thickness.It is not difficult to produce tubes with mica windows of area 3 cm.2 and about 2 mg./cm.2 thickness. Much thinner windows may be constructed using a grid with a known transmission factor to form a support for the very fragile mica required. Such grids prepared by a photographic and electroplating process may be obtained now with known transmission factors of 80 per cent. 01- more. Alternatively for the least energetic @-emitters such as W the sample may be inserted in the counter.6 In such cases the active sample may either be introduced as a December 19483 BfADDaCK THE MEASUREMENT OF BETA-ACTIVITY 647 active gas which forms part of the filling of the counter in which circumstances it is necessary that the gas shall not interfere in the electrical operation of the counter ; or the material may be introduced as a solid compound into the screen-wall type of counter described by Libby.’ The use of the latter type of counter is necessarily tedious and should be avoided where possible.l4C may be determined directly as carbon dioxide in an internal counter if carbon disulphide vapour be added otherwise the counter will show no workable plateau.8 In addition to corrections for decay measurements of specific activity that is to say activity per unit mass of material require in general to be corrected for coincidence and absorption losses. Corrections for temperature-induced changes in the efficiency of the counter have been discussed already.The coincidence correction can be made when the mean dead time of the counter after each pulse has been measured and the counting rate on the sample has been determined. Thus if T is the dead time which is equal to the length of the quench pulse for the circuit mentioned above N = No/(l-NOT) where No is the observed counting rate and N the true counting rate. This equation is applicable only when the correction is small and the Geiger - Miiller tube is inactivated for a definite time after each pulse (see Kurbatov and Mann9 and Gnedenkolo). The dead time of the counter and recorder may be measured electrically or by the use of two approximately equal sources (Kohmanll and Beersf2). However since the dead time of some recording circuits depends on the counting rate and the pulse size it is generally best to prepare an empirical correction curve by measurement of the activity of a series of sources prepared by the evaporation of known volumes of a solution containing an unweighable quantity of a long-lived non-volatile /%active isotope.Corrections may also be made from the decay curve of a strong short-lived source. Except where the specific activity of the material is sufficiently high or the energy of its particles sufficiently great for the sample counted to be considered “infinitely thin,” ‘correc-tions must be made for absorption of the p-particles within the sample. Three techniques may be distinguished. If sufficiently large quantities of the material are available or the !-radiation is sufficiently soft measurements may be made on infinitely thick samples that is to say samples thicker than the range of the particles emitted.The observed activity then bears a constant relation to the true specific activity which may be defined as the activity per unit mass of sample for an infinitely thin sample. It should be noted however that the ratio of the observed activity to the specific activity for infinitely thick s’amples is not indepen-dent of the composition of the sample because of differences in scattering power. A second procedure consists in diluting all samples to a constant mass per unit area with inactive material and thus obtaining a constant self-absorption correction which need not be deter-mined even for relative measurements. The difficulty lies in the necessity for homogenisation of the active and inactive materials both of which will be in general crystalline solids.Finally in the most general case the mass per unit area of the sample is determined and a correction made for the self-absorption. It has been found that although /&particles show a finite range in matter under certain geometrical conditions the reduction in the observable activity produced by the interposition of different thicknesses of aluminium foil between the source and the detector follows an exponential law (see Rutherford Chadwick and Ellisla). Theoretically no such absorption law is to be expected. Over a larger range of thicknesses the plot of the logarithm of the activity against the thickness of foil is usually concave to the axis of thickness.The greater the proportion of high-energy /3-particles in the spectrum of the source the greater is this deviation, and conversely. The most favourable geometric conditions are obtained by mounting the absorbing screen immediately in front of the counter window and keeping the construction of the source holder as light as possible to avoid scattered and secondary electrons. The sample should be mounted on a thin foil. Under these conditions many /3-emitters appear to exhibit exponential absorption for reductions in activity up to a factor of 2 or more. Like the range of the 6-particles this absorption coefficient or the corresponding half thickness is not much dependent on the nature of the absorber for the light elements and it may be expressed there-fore in mg./cm.2 With the heavy elements this is no longer true because the number of electrons per unit mass decreases owing to the decreased ratio of protons to neutrons in the nucleus.Expressions have been given relating this half thickness to the maximum energy of the /%ray spectrum concerned but in view of the empirical nature of this absorption relation and its very limited applicability their use is not recommended (Huber Lienhard Scherrer and W6fflerl4 and Percy14) $48 MADDOCK THE MEASUREMENT OF BETA-ACTIVITY [Vol. 73 Under conditions favourable to the above absorption law one can easily show (cf. Meyer and Schweidler16) that apt a,= - 1 -e-W where t = thickness of sample measured in rng/cm.2 p = mass absorption coefficient. a = observed specific activity = number of counts per unit time per gram of sample.a, = true specific activity = number of counts per unit time per gram of sample at zero sample thickness. This relation does not allow for back scattering within the sample. Since p is known to be nearly independent of the material for the lighter elements pt/(l -e-wf) will constitute a self-absorption correction factor which depends only on the mass per unit area of the sample measured. (Tables of this function are given by Steffen~onl~). It will be observed that this 1.02-1.01 -- 3.0 -1.2 COR R ECTlO NS 1.04 1 9 3 1.02 6 ~ I0 20 ~ Fig. 2. Correction factor 1 x is used with scales indicated. Correction factor 10 x applies if absorption half-thickness scale is divided by 10 December 1948 J MADDOCK THE MEASUREMENT OF BETA-ACTIVITY 649 function may be set up as a nomogram as shown in Fig.2. This nomogram has been found useful in making rough corrections for self-absorption with a variety of isotopes in the correction range 1.01 to 1-50. It must be emphasised that for very accurate work an empirical self-absorption correction curve m ~ s t be constructed. It has been found that such curves are frequently nearly exponen-tial over a small range with €4 = 2.2~4 where q is the self-absorption half-thickness and r ~ ) is the external absorption half thickness. This modification of the above approximate correction formula is brought about by the back scattering in the sample. (Cf. Broda Gueron and Kowarski.l*) In addition to these corrections some uncertainty is introduced into Geiger - Miiller counter measurements by the ill-defined “history” effects; that is to say the efficiency of the tube appears to fluctuate with its immediate previous treatment.A day’s operation at a high counting rate appreciably alters the shape and position of the plateau and the tube takes many hours to recover (cf. Spat9). The effect is small but makes high precision measurement almost impossible. Finally with respect to standardisation for absolute measurements accurate determina-tions can be made only by coincidence methods but rough standardisation of a /I-counting set may be made by means of a uranium or a radium D E F standard. An over-all efficiency combining the geometrical and electrical factors is calculated after allowing for absorption losses in the air between the sample and the counter and in the counter window.In the former determination a known weight of uranium is deposited as a uniform film on a foil. Evaporation of a solution of the nitrate in pyridine followed by ignition of the residue is one of the most. convenient ways of preparing a suitable foil. The sample is counted with a 20mg./cm.Z absorber screen in position to filter out the UX radiation. From the known decay constant of uranium the disintegration rate of the sample can be calculated and after correction for absorption in the film itself the absorber screen the air between the foil and the counter and the counter window the decay rate is compared with the observed counting rate. Uncer-tainties are introduced in the use of this calibration for any other active isotope owing to differences in the back-scattering effects.Ideally the calibration should be carried out with the isotope it is desired to measure. The radium D E F standard is made by electro-deposition of an equilibrium mixture of radium D E and F. The radium F is measured in an oc-counter of known or calculable efficiency and hence the /?-disintegration rate of the sample deduced. It will be seen that the measurements of 19-activity with about a 2 per cent. probable error is relatively straightforward but that the attainment of 0.5 per cent. probable error or better is a matter of some considerable difficulty. REFERENCES 1. Montgomery C. G. and Montgomery D. D. Phys. Rev. 1940 57 1030. 2. Stever H. G. Ibid. 1942 61 38.3. Korff S. A. and Present R. D. Ibid. 1944 65 274. 4. Palersky H. Swank P. K. and Greenshik R. BUZZ. Amer. Phys. SOC. 1946 21 No. 3 23. 5. Getting I. A. Phys. Rev. 1938 53 103. 6. “Preparation and measurement of isotopic tracers,” Ann Arbor Symposium 1946 p. 83. 7. Libby W. W. Phys. Rev. 1939,55 245; 1934,46 196. 8. Brown S. C. and Miller W. W. Rev. Sci. Instr. 1947 18 496. 9. Kurbatov J. O. and Mann H. B. Phys. Rev. 1945,68 40. 10. Gnedendko B. V. J . Expt. Theor. Phys. U.S.S.R. 1941 11 101. 11. Kohman T. P. Phys. Rev. 1944 65 63. 12. Beers Y. Rev. Sci. Instr. 1942 13 72. 13. Rutherford E. Chadwick J. and Ellis C. D. “Radiation from Radioactive Substances,” Cambridge 14. Huber O. Lienhard O. Schemer P. and W6ffler H. Helv. Plcys. Acta 1945 18 221. 15. Perey M.Comptes rend. 1944 218 714. 16. Meyer St. and Schweidler E. “Radioaktivitat,” Teubner Leipsiz. 17. Steffensen J. F. Skand. Aktuarietidskrift 1938 p. 47. 18. Broda E. Gueron J. and Kowarski L. Declassified British Report B.D.D. 114 (8/43). 19. Spatz G. Phys. Rev. 1943,63 462. Univ. Press London 1930. RADIO CHEMICAL LABORATORY UNIVERSITY CHEMICAL LABORATORY CAMBRIDG 660 WHITMORE THE MEASUREMENT OF RADIO-ISOTOPES [Vol. 73 The Measurement of Radio-Iso t opes BY F. €3. WHITMORE THE measurement of radio-isotopes presents a problem of a complex nature and its solution is an important matter in view of the tremendous expansion to be expected in the next few years in the use of such isotopes. The difficulties with which the investigator in this field is confronted are many and since each radioactive isotope has its own characteristic decay scheme it is not easy to formulate a general procedure of universal application.It can be said however that a means must be found of correlating the intensity of the radiation emitted by a particular source with the number of atoms disintegrating within that source in a unit interval of time. If /&decay involved the emission of only one j3-particle from each dis-integrating atom the difficulties would not be so great. The measurement therefore of radio-phosphorus s2P which undergoes this simple decay process1 (Fig. 1) is comparatively easy, although attention must be paid to the appropriate corrections for the loss of j3-particles by absorption between their emission from the parent nucleus and their initiation of a pulse in the counting tube.However some of the elements that are of use as tracers emit heterogeneous radiations which make a simple estimation of this type no longer reliable e.g. radio-zinc 6sZn (Fig. 2) produces during its decay process positive electrons accompanied by their annihilation radiation X-rays and y-rays.2,s All of these rays are capable of being detected by the Geiger -Miiller counter with varying degrees of efficiency. Fig. 1 Fig. 2 The variation of the efficiency of a counter with the type and energy of the radiation is important. In the case of /?-rays nearly every j3-particle that enters the sensitive volume of the counter initiates the avalanche of electrons resulting in a pulse at the collecting wire.Estimates of the efficiency of this process vary but it is usually greater than 95 per cent.4 Ionisation by a y-ray photon on the other hand occurs mainly by tearing away and energising electrons from neutral atoms of the counter wall material by the photo-electric and Compton effects. This is not an efficient way of starting an avalanche,-possibly as few as one photon in one thousand produces a count. In a great many /&decay processes the emission of a p-particle is accompanied by the ejection of one or more photons. The ejection of the two types of ray is virtually simultaneous, the 7-ray usually following the /%ray within seconds. It is possible to compare two radioactive sources solely on the basis of the y-rays that are emitted notwithstanding the low counting efficiency using a counter and an “optical bench” type of apparatus of the same principle as that used in photometry.An additional correction for the absorption of ’y-rays in the air gap between the source and the counter is needed if this distance is large or if the rays are of low energy. The efficiency of a Geiger - Miiller counter with respect to y-rays ma December 19481 WHITMORE THE MEASUREMENT OF RADIO-ISOTOOES 651 be improved by the use of a cathode made of a heavy metal in which the number of electrons ejected photo-electrically and by the Compton effect is increased. The sequence of emission of a /I-particle followed by a y-photon has been used to determine, absolutely the activity of a radio-isotope specimen.616 The method employs the coincidence type of counting circuit which has found considerable use in cosmic ray work.The coincidence circuit is arranged in such a manner that neither of two Geiger - Muller counting tubes will register counts on the recording apparatus while only one tube is exposed to the radioactive source. Furthermore if both tubes are exposed to the radiation only the simultaneous arrival of rays in the two counters can trigger a pulse. Strictly the use of the word “simul-taneous” is not correct but rays arriving within one micro-second of each other can be regarded as simultaneous for the purposes of this description. This is because the resolving time of the electronic recording circuit is about one micro-second. The circuit required for this method of counting is rather more elaborate than the ordinary counting arrangement, but many types have been used.’ COlNWENW ClRCUlt Fig.3 Fig. 4 Suppose it is required to measure a sample of a radio-isotope which decays by the emission of a /?-particle followed by one photon. The specimen S is located between two counters and an absorber is arranged so that counter A receives y-rays only (Fig. 3). Since there is a factor of one thousand between the efficiencies of /I- and 7-detection counter B is effectively counting j3-rays only. Let N = number of disintegrations occurring per second in the specimen. N = number of counts per second recorded by counter A. Np = number of counts per second recorded by counter B. ey = net efficiency of counter A. ep = net efficiency of counter B. Nc = number of counts per second recorded with A and B operating in coincidence.Net efficiency is understood to mean the ratio of the number of pulses produced in the Then with counters working separately, N = Ne, and Np = Nep hence N Np = N2e ep counter to the number of disintegrations in the source in any given interval of time. With counters working in coincidence, N = Neyeg NY NP NC by division N = -Dividing N by 3.7 x lWo the number of disintegrations per second in one curie of material, gives the absolute strength of the source in curies 652 WHITMORE THE MEASUREMENT OF RADIO-ISOTOPES [Vol. 73 The above example is of a very simple case and the natural background rates of the counters have been omitted and the random coincidence rate has been neglected.The com-plexity of the method also increases as the decay scheme of the radio-element to be measured becomes more complicated. By solving the above equations eg and ey the efficiencies of the counters may be obtained and used subsequently in simple #?- and y-ray comparisons. The use of the coincidence method in measurement of the radio-elements is not restricted to absolute determinations. Coincidence counting can be applied to the determination of /?-activity in the presence of an unwanted background of y-radiation. The chance of a photon being detected simultaneously in both counters is very small since its chance of being detected in either counter separately is in the first place small. It is possible therefore to obtain a counting system with an extremely low background rate and yet possessing a high efficiency for the detection of /3-rays.Fig. 4 shows the lay-out of such an arrangement. Similar reasoning will show how the identification of a radio-isotope can be carried out with two counters in coincidence. The characteristic range of the j?-particles is determined by interposing foils between the specimen and the counters. Low sensitivity of the apparatus to y-rays is of great benefit in removing the exponential y-ray curve which is superimposed upon the /%ray spectrum curve when a single counter is used and the maximum range of the j?-rays is obtained in a direct manner from the thickness of aluminium required to stop them. An interesting application of coincidence counting is to be found in tracer experiments in vivo.In many of the experiments involving the tracing of a radio-element in the body of a living animal trouble is experienced owing to the lack of resolution in locating the point at which the isotope has its highest on cent ration.^,^^^^ Radiations being emitted in all direc-tions from the active atoms result in the substance appearing to be spread over a wide area. A lead shield with a collimating system of holes improves the resolution but it is cumbersome and can be criticised on account of the secondary radiation produced within the heavy metal. Two counters in coincidence however are directional in their behaviour and will detect only those radiations moving in such a direction as to penetrate them both. Hence they provide a convenient probe for locating radioactive material when conditions allow the use of a quantity of tracer sufficient to give a satisfactory coincidence counting rate.It has been possible in this short paper to mention only a few of the aspects of the subject of measurement and standardisation of radioactive isotopes. A great deal of work remains to be done before a satisfactory state of affairs exists and since it is hoped to make therapeutic use of some of these isotopes the need for accurate measurement is imperative. Particular mention has been made of the use of the method of counting coincidental arrivals of rays at two counters because it appears that this is an important technique which after further development may help to clear up the present unsatisfactory state of radioactive measurement. Recent reportsU indicate that the position in the United States of America is similar to that which exists here.It is also reported (ibid.) that at Chalk River consideration is being given to the use of coincidence measurements to determine counter efficiencies. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. REFERENCES Lyman E. M. Phys. Rev. 1937 51 1. Watase Y. Itoh J. and Takeda E. Proc. Phys.-Math. SOC. Japan 1940 21 626. Deutsch M. Roberts A. Elliott L. G. Phys. Rev. 1942 61 389. Korff S. A. “Electron and Nuclear Counters,” Van Nostrand Co. Inc. 1946. Dunworth J. V. Rev. Sci. Instr. 1940 11 167. Wiedenbeck M. L. PAYS. Rev. 1947,72 974. Mandeville C. R. and Scherb M. V. Ibid. 1948 73 90. Moore F. D. and Tobin b. H. J . Clin. Investigation 1942 21 471.- Ibid. 1943 22 155. 7- Ibid. 1943 22 161. Goldie E. A. G. Medical Research Council T.E.S. 12 (1947). DEPARTMENT OF PHYSICS UNIVERSITY OF BIRMINGHAM Mas.ch 194 December 19481 WINTER THE MEASUREMENT OF ABUNDANCE RATIOS 663 The Measurement of Abundance Ratios of Non-Radioactive Isotopes BY E. R. S. WINTER THE MASS SPECTROMETER THIS paper is concerned with the determination of isotope abundance ratios of non-radioactive elements and in particular with the mass spectrometer which is the most versatile instrument available for this purpose. The determination of these ratios for some of the lighter elements-notably oxygen nitrogen and hydrogen and to a certain extent sulphur and carbon-is a matter of some importance since radioactive isotopes of the first three elements do not possess the properties necessary to make them useful in tracer experiments.Special methods have been devised for oxygen and hydrogen and these and others will be dealt with by my colleague Dr. E. R. Roberts,ls but none of these methods has the wide range of application of the mass spectrometer. The instrument is as is well-known a development of the method of positive-ray analysis devised by Sir J. J. Thomson; the first mass spectrographs were built by Astonl in this country, followed a little later by Dempster2 in the U.S.A. The early instruments are more properly called mass spectrographs since they were designed primarily for the accurate determination of the masses of the various isotopes; more recently attention has been focussed on the determination of the relative abundance of given isotopes and this requires a mass spectro-meter.The design requirements for these two objectives are not the same;- it is of course, with mass spectrometry that we are concerned here. The instrument consists of a means of forming a stream of positive ions derived from the element to be analysed (which may be used in the elementary state or in the form of a simple compound e.g oxide halide or hydride) ; these ions are then subjected to suitably orientated electrical and magnetic fields which sort out ions of different masses and bring those of each mass to a focus at a different point in space. A Faraday cup suitably positioned will collect each mass in turn if one of the two fields is varied in a systematic fashion the abundance of each mass in the original sample is proportional to and can therefore be calculated from the magnitude of the positive ion current carried by it.In early instruments photographic methods were used to record the ions and to assess their approximate abundance but now a direct measure of the current is attained by means of a suitable D.C. amplifier. The first mass spectrometer of a satisfactory simple design for general use was that of NieP and it is safe to say that the majority of modem instruments are derived directly from his basic design. Nier used the method of direction focussing which can be best illustrated by a diagram (Fig. 1). Ions are formed at the source S and are accelerated through an electrostatic field V / Fig. 1 (500 to 2OOO volts usually).Since the ions (of mass m) are initially almost at rest we may find their velocity v asithey leave the electrostatic field by means of the relation Ve = m79/2, * ' (1) (2Ve)4 whence ZJ =- m This assumes as is normally the case that the ions carry a unit charge e 654 WINTER THE MEASUREMENT OF ABUNDANCE RATIOS [Vol. 73 The ions travel from S at velocity v in a straight line until they enter at right angles the influence of a powerful electromagnet of field strength H; this bends their course through the arc of a circle of radius r where we have mu2 r * . (2) Hev= - Elimination of v between (1) and (2) gives .- (3) 2Vm H2e . * r2= -If the magnet pole pieces are shaped as shown then the ion beam will be bent through an angle 8 will leave the field at right angles and will be brought to a sharp focus at 0 where S 0 and F the apex of the effective magnetic field lie on a straight line.In practice S and 0 are fixed by the construction of the mass spectrometer tube and the three points are brought into alignment by adjustment of the position of either the tube or the magnet; the position is not usually critical (in the plane of the paper) to within 0-5 mm. with the type of tube described below. Tubes have been described with 8 = 60" 90" or 180"; the last type involves the construction of a large magnet with semicircular pole faces between which is placed the whole of the mass spectrometer tube. The 60" or 90" instruments are therefore more common, since smaller magnets are required only the angle of the tube being between the pole faces; this smaller magnet taking less power simplifies the electronic requirements for the control circuit.It is obvious from equation (3) that for given H and V only ions of one mass are brought to a focus at 0; other masses will be focussed at 0 by changing H or V. It is usual when determining abundance ratios of a single element for which of course the mass numbers are nearly equal to vary V only since a variation in the current through the electromagnet intro-duces awkward hysteresis effects. However for work of high precision the abundance figure obtained by varying V with H constant should be checked by varying H with V constant. A modern mass spectrometer tube working on the above principle and designed for the analysis of gaseous samples only is illustrated in Fig.2 (refs. The tube from S to 0 is of / u, Fig. 2 copper about 1 inch in outside diameter bent accurately to shape and flattened to 0.5 inch thickness at the bend; copper-to-glass seals are hard-soldered on at U and V; the holes shown in the copper tube between S and U and 0 and V are to facilitate the continuous evacuation of the main tube. The radius of curvature is normally about 5 inches. The ion source is attached to S by a bushing which is keyed to the main tube so that the source may be removed for cleaning etc. and replaced in precisely the same position details of this source and of the potentials applied to it are shown in Fig. 3 (refs. 894). The filament of tungsten ribbon emits electrons which are drawn across the top of the slit in plate B passing through slits in the two ends of the ionisation box and are collected on the trap to which is applied a positive voltage to prevent secondary emission.The metal used for the plates forming the source and collector assemblies is usually a non-magnetic nichrome. The gas sample is fed into the top of the ionisation chamber and positive ions formed in the electron beam are repelled down through the slit in plate B by a small positive potential on the deflector plate A. The ribbon of ions is straightened up by the action of the voltages on the two D plates and passes through the slit in plate C into the analyser tube. A small external magnet is necessary to align properly the electron beam in the source and the December 19481 OF NON-RADIOACTIVE ISOTOPES 666 plates are needed mainly to counteract its effect and that of space charges in the ionisation region on the ion beam.The position of this magnet is critical. The various plates are separated by accurately ground Pyrex glass spacers and firmly bolted together. The leads to the plates are taken out through the 5-wire pinch-seal as shown. The collector assembly similarly consists of two plates with slits in them and a Faraday cup at the rear; the positive ion current passing through to the cup is fed through a single wire-to-glass seal by a short lead to the grid of the first valve of the D.C. amplifier. This valve with its grid leak and the various leads must be well shielded electrostatically and magnetically. The whole tube assembly must be accurately performed using a large jig; the type of thing required can be seen from a paper by Thode Graham and Ziegler.5 The merit of this design of tube due to Nie9 is that because of the absence of stopcocks greased joints gaskets and the like the tube can be wound with a heating furnace and outgassed at 300 to 400" C.which largely eliminates gaseous impurities (N, 02 CO, H20) that otherwise make accurate analysis of these masses very difficult. All-metal tubes have been described.6 A commercial instrument is manufactured in this country by Metropolitan-Vickers Ltd. of Trafford Park Manchester. An important point to note about the design of the tube is that whilst the slit from which the beam emerges into the analyser tube is only about 0-25 mm. wide the first exit slit is about 1.0 mm.wide; in consequence the accelerating voltage V may be varied over a v 1 i Electron I /Trap A B x - D C Plan of top plate Section through X - X Section through Y - Y Fig. 3. -small range before the positive ion current changes and the voltage - current curves have flat tops. This type of mass peak is valuable in abundance measurements since we can then "sit" on top of a peak and get an accurate value for the ion current relatively independent of small fluctuations in H or V. It is important when designing a tube to take stock of the masses it is wished to investi-gate so as.to be sure that the geometry is such that the peaks corresponding to the closest pair of the heavier masses will be adequately separated.The resohingpower of a tube may be expressed as (m/Am)ma. and this may be shown to be equal tcP r width of entrance slit + width of exit slit ' thus by arranging for flat-topped peaks i.e. using a wide exit slit we sacrifice some resolving power but for normal work which will only involve the lighter elements this does not matter. For instance to take typical dimensions when r = 126 mm.? entrance slit = 0-25 mm. wide, and exit slit = 1-0 mm. then 126 - 101 0-25 + 1.0 - resolving power 656 WINTER THE MEASUREMENT OF ABUNDANCE RATIOS Vol. 73 and this means that the tube should ideally separate the mass 100 peak from that of mass 101 , which is ample resolution for all the lighter elements e.g. 32s02(64) and %02(66) are among the heaviest molecules likely to be met with in most tracer work.The practical resolving power of an instrument is given by mass units between peaks mass analysed distance between peaks width of peak at base and with expert handling an accurately constructed tube will have a practical resolving power equal to the geometrical value.5 The effect of geometrical asymmetries of the tube or magnetic field upon the resolving power has been dealt with by Blears.' The auxiliary equipment necessary for a complete mass spectrometer is illustrated by the block diagram (Fig. 4) and these items may be considered in turn. Fig. 4 mm. of mercury in the main tube while the sample to be analysed is being let in through the capillary leak; this will mean a pressure of about 10-5mm. inside the ionisation chamber.A fast-working diffusion pump such as the Edwards Type 7 the pump described by Bull and KlempererJB or the Metropolitan-Vickers oil diffusion pump Type 03.B backed by a rotary oil pump using wide-bore (3 to 5 cm.) connecting tubing between diffusion pump and mass spectrometer tube will provide the necessary pumping speed. A cold trap must be included in the line and solid carbon dioxide will suffice as refrigerant; liquid air is rarely needed. (b) Electronic requirements-It is possible where work of low accuracy upon one or two elements only is contemplated to run a tube solely off batteries except for the D.C. amplifier, but for routine measurements of accurate abundance ratios of a number of elements properly designed electronic circuits are essential. Suitable circuits so far described unfortunately all require U.S.A.-type valves; reference may be made to recent papers by Hipple Grove and Hickman,D by Nier6 and by Thode Graham and Harkness.* I have myself built the circuits described in the last-mentioned paper and find them entirely satisfactory in operation.(c) Mani+uZation of sam+Zes-Gas samples are normally sealed in small glass tubes provided with a drawn-out thin-walled capillary tip which may be inserted into a conventional vacuum seal-break assembly. The gas handling line can be very simple consisting of the seal-breaker gas reservoirs manometer and possibly Pirani gauge and Toppler pump; it is necessary merely to provide means of adjusting the pressure of sample behind the leak into the mass spectrometer tube to such a value that the pressure in the ionisation chamber is about 10-6 mm.It is further advisable to let the sample into the mass spectrometer through a cold trap to keep back water vapour and organic impurities. A single-stage rotary oil pump will normally provide the vacuum needed in the gas handling line. The question of fractiona-tion of the sample during diffusion into the ionisation chamber does not arise with isotopes of one element (except mixtures of H with DJ but if analyses of hydrocarbon1* or general gas mixtures be contemplated the design of the capillary leak and gas handling line needs careful th0ught.u It may be noted that most work will involve the use of gaseous samples but of course relatively non-volatile materials may be analysed by altering the design of the ion source somewhat.lJ2 PERFORMANCE Mass spectrometers of the design outlined above are capable of measuring the abundance ratios to an accuracy within 0-3 per cent.or better when the least abundant isotope is present (a) VaczauM-This must be kept down to 1 x lo-@ to 5 December 19481 pu’ ON-RAD I 0 ACTIVE I SOTOPES 667 to the extent of 1 per cent. or more (the precision falls off with lower enrichments) but this requires extreme care and expert personnel; the beginner should obtain figures to 3 per cent. accuracy and soon push his standard up to 1 per cent. which is adequate for all except the most exacting work. I t is important to realise that although the internal consistency of results on one machine may be high different results may be obtained upon another instrument.This is due to the possibility of discrimination ions of one mass type being produced in the beam to an extent consistently greater (or less) than their true concentration in the sample: the causes of this are complex and cannot be dealt with here.l8 The time for one analysis involving two or three masses is only a few minutes but the time taken to change from one sample to another and to pump out from the gas-handling line and ion source all traces of the first sample may be as long as 30 minutes and it is usually this that sets the limit upon speed of analysis. It is desirable to interpose frequent checks on the instrument by analysing a standard sample of the gas that is being investigated e.g. when determining abundance ratios of the carbon isotopes in a number of samples of carbon dioxide one in every five or six analyses should be of a sample of normal carbon dioxide.Speed and accuracy may be increased by a number of means chief among which is the use of an automatic recorder to provide a rapid trace of the variation of the ion current collected at the Faraday cup as H or V is varied; a rapid pen recorder14 has been used most frequently but a photographic trace16 is a cheaper alternative. Some form of recorder is essential if general gas analysis (e.g. of hydrocarbon mixtures) is contemplated or if the elements dealt with give rise to more than about three mass peaks (such as Xenon,14 which gives 9). REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.Aston F. W. see for instance “Mass Spectra and Isotopes,” C.U.P. 1940. Dempster A. J. Phil. Mag. 1916,31 438. Nier A. O. Rev. Sci. Instr. 1940 11 212. Graham R. L. Thode H. G. and Harkness A. L. J . Sci. Instr. 1947,24 119. Thode H. G. Graham R. L. and Ziegler J . A. Canadian J . Res. 1946 B. 23 40. Nier A. O. Rev. Sci. Instr. 1947 18 398. Blears J. Int. Congress of Pure and Applied Chemistry 1947 in the press. Bull C. S. Klemperer O. J . Sci. Instr. 1943 20 179 BUZZ. B. Pal. No. 652898-1941. Hipple J. A. Grove D. J. and Hickam R. W. Rev. Sci. Instr 1945 16 69. Brewer A. K. and Dibeler V. H. J . Res. National Bureau of Standards 1945 35 126. Honig R. E. J . AppZ. Physics 1945 16 646. Nier A. O. Ney E. P. and Ingram M. G. Rev. Sci. Instr. 1947 18 191. See for instance Nier A.O. Phys. Rev. 1938 53 282. Bleakney W. Amer. Phys. Teacher 1936,4 12. Coggleshall N. D. J . Chem. Physics 1944.12 19, Coggleshall N. D. and Jordan E. B. Rev. Sci. Instr. 1943 14 125; J . AppZ. Physics 1942, 18 526. 14. Lossing F. P. Shields R. B. and Thode H. G. Canadian J . Res. 1947 B. 25 397. 15. Smith P. T. Lozier W. W. Smith L. G. and Bleakney W. Rev. Sci. Instr. 1937 8 61. 16. Roberts E. R. ANALYST 1948 73 657. Phys. Rev. 1918 316. Fowler R. D. Rev. Sci. Instr. 1935 6 26. DEPARTMENT OF INORGANIC AND PHYSICAL CHEMISTRY IMPERIAL COLLEGE OF SCIENCE AND TECHNOLOGY LONDON S.W.7 The Measurement of Stable Isotope Abundance Ratios BY ERIC R. ROBERTS DR. WINTER’S paper1 leaves little doubt as to the best method available for the accurate determination of isotope abundances.The two disadvantages of the mass spectrometer, namely its high initial cost and the need for a high degree of operational skill are however, very real and it is desirable therefore to discuss alternative methods which although they may be incapable of such great accuracy and may demand exceptional care in the chemical purification of the samples are nevertheless relatively cheap to initiate and involve techniques well within the range of the chemist. Such methods must be concerned with the measurement of those properties that depend on mass and in practice have been confined mainly to com-parative determinations of density (gases and liquids) and thermal conductivity (gases) , although in some early work on heavy water the refractive index was used.A. DENSITY METHODS (i) Gas density-Determination of gas densities by direct weighing is generally impractic-able because the achievement of even a moderate degree of accuracy necessitates the use o 658 ROBERTS THE MEASUREMENT OF STABLE ISOTOPE [Vol. 73 very large samples; but comparative measurements made with the buoyancy balance may give sufficient precision on relatively small gas samples. This instrument developed to determine atomic weights’s2 and the approximate molecular weights of the hydrides of boron and silicon: is best constructed of quartz and suspended on quartz fibres; the exposed surfaces on both sides of the fulcrum are equalised as accurately as possible to minimise errors introduced by adsorption of the gases on the balance.Such a balance may be made extremely sensitive to changes of pressure in the surrounding medium and if the pressures of the sample and of a reference gas of known density are severally adjusted to bring the beam of the balance to the same null point then if the temperature throughout the operation has been kept constant the ratio of the densities of the two gases is in the inverse ratio of the “balancing pressures.” The sensitivity of the buoyancy balance is related to its size and a compromise must be found between the accuracy of measurement sought and the volume of sample available. Reduction of the working pressure while permitting the use of a smaller sample is limited in usefulness by the absolute sensitivity of the balance (which is largely determined by the volume of the buoyancy bulb and the dimensions of the suspending fibres).Thus with a mixture of hydrogen and deuterium containing 1 per cent. of D, the balancing pressures must be measured to within 0.001 mm. of mercury at a working pressure of 10 mm. if the deuterium content is to be determined to within one part in a thousand; if the balance case has a volume of about 100 ml. this would require a sample of 1 to 2 ml. at N.T.P. This example illustrates all the factors to be considered; for samples ten times as large the pressure readings need be only to within =t 0.01 mm. of mercury. In this connection it must be pointed out that the balance will in fact be poised only over a short range of pressure and that the more sensitive the balance the shorter is this range.The working range must therefore be decided (on grounds of desired accuracy and available sample size) before construction; from this point of view the simple instrument is not very flexible. I t was used4 to determine the extent of interchange between deuterium oxide and the hydrochlorides of some aliphatic amines and in this work the molecular weights of the deuteramines were measured to rather better than f 0.01 units. The samples available had a volume of about 60ml. at N.T.P. and a balance poised at about 400mm. of mercury was used. The accuracy of measurement was enhanced by using the corresponding light amine contained in a duplicate balance case as the reference gas keeping all volumes absolutely constant and measuring the difference in balancing pressures on an oil manometer; the latter could be read to an accuracy equivalent to f 0405 mm.of mercury. In this way expensive apparatus was avoided. The necessity for extreme chemical purity of the samples and reference gases however remained. For elements of higher atomic weight the attainable accuracy falls off rapidly because of the smaller relative differences in physical properties. The data for deuterium therefore represent the optimum limits of the method. (ii) Liquid density-The most fruitful application of liquid density measurements has been to the determination of deuterium and to a smaller extent l 8 0 in water. The most satisfactory method for this purpose is the determination of the flotation temperature of a calibrated In its original form when it was used to explore the variation in deuterium content of water from many natural sources both mineral and organic the method involved the use of a large float and a sample of about 1 litre but it was later modified to handle samples of a few ml.without any loss in accuracy and in fact with sufficient care the micro-method yields an even greater accuracy. The rate of rise and fall of the float is measured over a small range of temperature in a carefully thermostated apparatus (f 0*01” C. or better) and the reciprocals of the rates plotted against temperature. A straight-line graph cutting the Zero-rate axis at the flotation temperature is obtained from which the density of the sample may be calculated to within f 1.5 p.p.m. if the float has been standardised in a suitably purified sample of ordinary water.Generally it is unnecessary to make this calculation the results being expressed in terms of the differencezin the flotation temperatures of the sample and the standard. The following data indicate the sensitivity of the method in order to determine to within f 0.1 per cent. the content of D20 in water containing 1 per cent. of D20 using a float already described,6 the flotation temperature must be determined to within f 0~001” C. It is significant that reproducibility of this order of accuracy is possible though difficult. The technique has been used for investigating exchange reactions between deuterium oxide and hydrogen in complex salts such as cobaltammines;7 it has also found use in following the progress of lSO concentration during the distillation of water and the interchange of thi December 19481 ABUNDANCE RATIOS 659 isotope between water and inorganic oxy-anions.* Considerable care must be taken in purifying the sample,6 especially in view of the marked solvent action of water.As with gas densities the sensitivity of the method decreases rapidly as the atomic weight increases. An alternative liquid density method is afforded by the use of the micro-pyknometer, to which the same considerations regarding purity of sample and adequate control of tempera-ture apply; there is again a practical limit to the accuracy obtainable with a sample of given volume. In another inethod in which the sample size is only one drop the sample is suspended in an immiscible liquid and its rate of rise and fall over a small temperature range is measured.The sample itself is in fact the float and its flotation temperature may be determined as before. The difficulties of purity are doubled here since both liquids must be completely free from any matter that is mutually soluble or that may so modify the conditions at the interface that complete immiscibility is not achieved. Bearing in mind these additional difficulties it is doubtful whether the method offers such a high order of accuracy as the silica float method; it does have the advantage of requiring only a minute sample. Finally an effort has been made to determine isotope abundances by measuring the densities of fused salts. B. THERMAL CO?rr’l~CCTIVITY The measurement of the therinal conductivity of hydrogen gas was used initially for the analysis of mixtures of ortho- and para-hydrogen.The thermal conductivity cell consists of a vessel of gas through which passes a resistance wire which forms part of a Wheatstone bridge. The resistance is heated by an electric current and the rate of conduction of heat away from the wire through the gas to the carefully thermostated wall of the cell is reflected by a change in the resistance. The original method was niodified10J1s12 for the analysis of hydrogen-deuterium systems; a very small sample of gas may be used (0.005 ml. at N.T.P.) and by operating the cell at relatively high pressures (50 mm. of mercury) errors due to variation in the accommodation coefficients of the gases on the resistance wire are virtually eliminated.The gauge must be calibrated by means of mixtures of known composition and it is generally found that the equilibrated system (H + D + 2HD) behaves slightly differently from the simple mixture of H and D,. Thus if in the experiment any possibility of partial con-version to HD exists the sample to be analysed should be equilibrated before measurement is made. The differences in thermal conductivity between these two systems is most marked when roughly equal proportions of the two isotopes are present so that attention to this point is most necessary in this region of composition. Moreover even at the high pressures suggested, thermal conductivity is dependent on pressure and each sample should be brought to a standard pressure ( f- 0.2 mm.) before analysis.Since the changes in resistance measured are very small it is essential that the ratio arms of the bridge be kept at constant temperature and thoroughly insulated. When all these sources of error have been controlled and with a suitably purified sample, an accuracy to within 0.2 to 0.7 per cent. is readily attained depending on the actual com-position of the sample. The theory of the thermal conductivity gauge has been reasonably well worked out for the H2-D and H,-HD-D systems but is insufficiently complete to enable the behaviour in other gases to be predicted; lack of certain molecular data also pre-cludes such prediction but there are no a priori reasons why thermal conductivity should not be a suitable property to measure for the isotopic analysis of elements other than hydrogen.As in the other methods discussed rigorous purification of the sample is essential although Bolland and Melvillell showed that hydrogen - deuterium samples could be analysed in presence of a third gas e.g. nitrogen or carbon monoxide. The use of such small samples suits this method to kinetic work in which the withdrawal of the sample must not change the conditions in the reaction vessel. The photosensitised exchange reaction between deuterium and phosphinelO and the catalytic exchange between deuterium and hydrocarbons12 are typical examples of its application. NOTE.-&. Newton Friend raised the question of the measurement of refractive index in the analysis of mixtures of water and deuterium oxide. Consideration of the accuracy of measurement needed to give a final figure comparable with that obtained using water density measurements shows that the limit is determined primarily by the efficiency of the thermostatic control.It is considered that this would be no easier with refractive index measurements tha 660 AKROL TRACERS IX BIOCHEMICAL IKVESTIGATIOSS [Vol. 73 with density determinations and that the former method does not offer any marked advantages over those described above. KEFEREh’CES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11 12. 13. SteeIe and Grant Proc. Roy. SOC. 1909 82 680. Aston, Whytlaw-Gray R. PYOC. Roy. Sor. 1933 134 7. Whytlaw-Gray and Woodhead J . Chern. SOC., Stock A. and Ritter G. 2. Phvsik. Chew. 1926 119 333; 124 204. Roberts E. R. Emeleus H. J. and Briscoe J .Cheni. SOC. 1939 41. Briscoe H. V. A. el a. Ibid. 1934 1207. -,- Ibid. 1937 1492. Abderson Briscoe and Spoor Ibid. 1943 361. Winter E. R. S. Carlton and Briscoe H. V. A. Ibid. 1940 131. Bonhoeffer K. F. and Harteck P. Z . Physikd. Chem. 1929 B. 4 113. Farkas A. and Farkas, Melville H. W. and Bolland J. I,. Ibid. 1937 160 384. Bolland J. L. and Melville €3. W. Trans. Far. SOC. 1937,33(2) 1316. Trenner N. R. J . Chem. Phys. 1937 5 382. Winter E. H. S. ANALYST 1948 73 653. IMPERIAL COLLEGE OF SCIENCE AND TECHNOLOGY Gray and Ramsay Ibid. 1910,84 536. Ibid. 1914 89 440. 1933 846. L. Proc. Roy. SOC. 1934 144 467. DEPARTMENT OF INORGANIC AND PHYSICAL CHEMISTRS LONDON S.W.7 Tracers in Biochemical Investigations BY W. J. ARROL THE principle of tracer technique is by now very well understood.It is that any element with an unnatural isotopic composition if introduced into a chemical system will betray its presence through measurement of the abundance of the unnatural isotope whether this be stable or radioactive. In biochemical systems in particular tracer methods have in recent years provided much information so that it is not surprising that many of the best examples of the use of these methods are to be found in the biochemical literature. It is of more use to consider a few isolated examples of the experiments possible with tracers than to attempt a survey of all the work done so far. Most of the examples that will be quoted have been carried out with the eight-day half-life radio-iodine 1311 which decays with emission of p- and y-rays.In all tracer work it is an element that is labelled and it is often necessary to identify the compound or compounds into which the element has been incorporated this being done by the chemical carrier technique. A good example of the technique is the identification of compounds into which radio-iodine has been incorporated after the administration of radio-iodide to surviving thvroid tissue. The chemical forms in which iodine is known to exist in the body are iodide di-iodotyrosine and thyroxine the latter two amino acids being combined in protein molecules while in the thyroid itself. Morton and Chaikoff incubated sliced thyroid tissues of dog sheep or rat for 24 hours in a bicarbonate-Ringer’s solution to which radio-iodide had been added.After hydrolysis they first removed excess radio-iodide by adding potassium iodide as carrier oxidising to iodine and extracting with carbon tetrachloride. They then carried out an extraction procedure which ought to extract thyroxine from the hydrolysate and found a small radioactive residue. A relatively large amount of non-radio active thyroxine was added to the residue the thyroxine was taken up in 0.1 N potassium carbonate and crystallised as the potassium salt. Five crystallisations were carried out, and at each crystallisation a little inactive di-iodotyrosine was added to “wash out” any radiodi-iodotyrosine that might be present. After the first recrystallisation the specific activity (activity per unit weight) of the thyroxine was found to be constant.Thus the inactive thyroxine could not be separated by crystallisation from the radioactive iodine of the residue and was acting as a carrier for it. Such crystallisation to constant specific activity is good although not quite conclusive evidence for the chemical identity of radio-active residue and inactive material added. By means of crystallisation to constant specific activity Morton and Chaikoff showed 1311 to be recoverable from thyroid tissue in the forms of iodide di-iodotyrosine and thyroxine. No other chemical forms were observed and the sum of these fractions measured separately were generally close to 100 per cent. of the activity originally added December 1948 J ARROL TRACERS IN BIOCHEMICAL INVESTIGATIONS 661 A recent development in chemical carrier technique is the use of chromatographic systems for the attempted separation of radioactive residue and inactive carrier.Again failure to separate the two is good evidence of chemical identity. In determining the precursor or precursors of a compound in a system the tracer technique has been used extensively particularly in living animals and micro-organisms. Labelled compounds which are likely to be the precursors of the compound in question can be syn-thesised and it can be shown experimentally which are incorporated into it with high effi-ciency. More precise information can sometimes be obtained by studying in a living animal the variation of the specific activities with time of two compounds. Zilversmit Entenman and Fishler2 considered theoretically the relationship which must hold between the specific activities of a labelled compound B and its immediate precursor A in a tissue after a single dose of a radioactive substance has been administered.They found that in the case when A is the immediate biological precursor of B the rate of variation with time of B’s specific activity must be proportional to the difference between the specific activities of A and B. Taurog and ChaikoP used this method for showing di-iodotyrosine to be the immediate precursor of thyroxine in vivo with the aid of radio-iodine 1811 administered to rats as radio-iodide. They used rats of selected strains raised on the same diet in which case they found results for individual rats to give agreement good enough for group averages to be accepted with confidence.The rats were killed at intervals of a 1,4 14 and 50 hours after administra-tion of radio-iodide and the specific activities of di-iodotyrosine and thyroxine from their thyroids were measured the specific activities being related to the iodine in the two organic compounds. The results were in full agreement with the postulate that di-iodotyrosine was the precursor of thyroxine. The distribution on the microscopic scale of a /3-active isotope in a specimen of tissue or in any small system can be studied by one variant or another of the radio-autographic tech-nique. With thyroid tissue for example a dose of a suitable radio-iodine is given and after about 48 hours tissue is taken and sections are cut in the usual way. If the section is pressed against a photographic plate for a time sufficient for the /I-rays to expose the plate this can be developed and compared with the section.The presence of local concentrations of the radio-iodine in the section will show up as areas of blackening in the corresponding position on the photographic plate. A variation of the method due to Pelc4 has several advantages. In this a stripping film is floated on to a ready-prepared section and dried in place. After exposure the emulsion is developed and the areas of blackening in the emulsion and the accumulations of radioactivity in the specimen are exactly superimposed. According to measurements of Stevens5 with exposure carried out by means of Pelc’s method local con-centrations of 1311 2.5 microns apart are resolved in the radio-autograph.A technique that has already been of use in a variety of different investigations is the isotope dilution technique. This was introduced originally by Rittenberg and Fosters for the analysis of fatty acids and amino acids in complex mixtures If a system contains a particular compound which is to be assayed the compound must first be synthesised with an isotopic label radioactive or stable. If x grams of the compound with C atom per cent. excess of a stable isotope are mixed evenly with the system and from a sample the compound is purified and then shows C atom per cent. of label because of its dilution withy grams of isotopically normal compound the amount y grams of compound originally in the system is given by:-y = ( . - l > ” The advantages of the dilution method include the fact that the size of the sample is not very important and the most rigorous methods of purification may be applied to the compound, even to the extent of losing a large proportion of it providing enough is left to carry out a mass spectrometric analysis.In the case of radioactive measurements C and C would refer respectively to the specific activities of the added labelled compound and the finally purified compound recovered from the system. Many of the applications of radioactive tracers in particular depend on the fact that exceedingly small amounts of material are readily measurable. For example something of the order of g. of carrier-free phosphorus 32 or iodine 131 would be measurable to within f 2 or 3 per cent. In a review on artificial radioactivity as long ago as 1940 Seaborg’ considered many of these applications including some in the field of analytical chemistry 662 GRIDGEMAX GIBSOX AKD SAVAGE CHROMATOGRAPHIC ESTIMATION [VOl. 73 Only now that counting equipment is becoming available comtnercially will it be possible in many laboratories to introduce radioactive techniques and exploit their possibilities both for research and in routine measurements. REFERENCES 1. Morton M. E. and Chaikoff I. L. J . BioZ. Chem. 1943 147 1. 2. Zilversmit D. B. Entenman C. and Fishler M. C. J . Gen. PhysioZ 1943 26 325. 3. Taurog A. and Chaikoff I. L. J . Biol. Chem. 1947 169 49. 4. Pelc S. R. Nature 1947 160 749. 5. Stevens G. W. W Ibid. 1948 161 432. 6. Rittenberg D. and Foster J . B i d . Chem. 1940 133 737. 7. Seaborg G. T. Ckem. Reviews 1940 27 199. 17 BLOOMSBURY SQUARE LONDON W.C. 1 COLLEGE OF THE PHARMACEUTICAL SOCIET

ISSN:0003-2654    

DOI:10.1039/AN9487300644

出版商:RSC    

年代:1948

数据来源: RSC

摘要:

662 Chromatographic Estimation of Vitamin A [Vol. 73 in Whale-Liver Oil BY N. T. GRIDGEMAN G. P. GIBSON and J. P. SAVAGE (Read at a Joint Mee€ing of the Xorth of England Section and the Physical Methods Group on October 2nd 1948 at Liverpool) INTRODUCTION DIRECT spectrophotometric estimation of vitamin A scil. E :&. (328 mp) x 1600 = Interna-tional Units per gram is not specific because differentiation between the absorption of the vitamin itself and whatever superimposed “irrelevant” absorption may occur is impracticable. In marine liver oils the commonest source of the vitamin the vitaminically inert compounds absorbing ultra-violet light may be divided into two groups depending on whether or not they are saponifiable. The saponifiable contribution is usually small; the EiZ.328 mp value of the glycerides is of the order of 0-2 which is less than 1 per cent. of the absorption of potent oils; while even at the comparatively low potency of 10,OOO I.U. per gram the glyceridic contribution is only about 3 per cent. In oils of lower potency (this includes the important case of cod-liver oil) the glyceridic absorption may be relatively high , but can be eliminated by saponification and removal of the soap i.e. estimation of “E value via unsap. ” The second group of compounds absorbing “irrelevantly” cannot of course be saponified away and in fact no wholly satisfactory method of elimination or allowance has hitherto been available. The substances concerned are for the most part structurally related to vitamin A and although their total effect on the spectrophotometric assay of the majority of commercial samples is small they can on occasion lead to seriously misleading results.Two particular cases in which direct E values may cloak irrelevances amounting to M) per cent. or more are noteworthy first that of heavily oxidised oils containing appreciable quantities of oxy-derivatives of vitamin A absorbing at Amax. = 270 to 290 mp; secondly, that of whale-liver oil whose vitamin A is invariably accompanied by biologically inactive materials some saponifiable and some not that absorb appreciable quantities of ultra-violet light. Highly oxidised oils are uncommon but whale-liver oil is a rich source of vitamin A and its analysis of considerable importance. Whale-liver oil has an absorption curve maximising in the region 290 to 310 mp and its complexity has long been re~ognised.l*~*~+* Some progress had been made in its resolution by solvent partitioning 10 years ago (Pritchard et aP).In 1943 Embree and Shantzs separated the main contaminant and called it kitol; it absorbs maximally at 290 mp. But small quanti-ties of other non-saponifiable substances with absorption peaks below 300 mp are almost invariably present. Moreover there is evidence that certain unidentified acetone-insoluble constituents absorb strongly in the ultra-violet which ties with the observation that E values “via unsap. ” are often considerably lower than the “gross” E values. Biological work carried out in these laboratories during the 1930’s on the vitamin A potency of whale-liver oils led to the conclusion that on an average about one-third to one-quarter of the gross absorption at 328 mp was irrelevant.A blanket factor of 1200 was there-fore used to convert gross Ei& 328 mp to I.U. per gram. The need for a less empirica December 19481 OF VITAMIN A IN WHALE-LIVER OIL 663 analytical method is clear and to this end Morton and Stubbss have developed a method wherein the irrelevant contribution is trigonometrically allowed for in the interpretation of the absorption curve. The present paper describes another approach that of chromatographic elimination of the irrelevant material and isolation of the pure vitamin A fraction. The method is based on the fact that the main components of the unsaponifiable fraction of whale-liver oil are selectively adsorbed on weakly active alumina in this order anhydro-vitamin A < oxidised vitamin A < vitamin A (alcohol) < kitol < sterols < selachyl alcohol.The technique consists of depositing the material on the column from a non-polar solvent and developing and eluting the chromatogram with solvents of progressively increasing polarity. The eluate is collected fractionally and Carr - Price spot tests are used to identify the vitamin A portions from which aliquots are bulked for spectrophotometry. METHOD The isolation of the unsaponifiable fraction of the oil must obviously be carried out with Saponify 5 g. of oil with 40 ml. of ethanol and 5 ml. of 60 per cent. aqueous potassium hydroxide solution adding 0-05 g. of quinol as antioxidant. A saponification time of at least 25 minutes is needed.Wash into a separating funnel with water and ethanol, adjusting the quantities to ensure a final concentration of 40 per cent. of ethanol and 2-5 to 4 per cent. of soap. Extract with one 1Wml. portion and at least three Wml. portions of a mixture of equal parts of redistilled ether and light petroleum (boiling range 40” to 60” C.). Wash the combined extracts with four 50-ml. portions of 40 per cent. aqueous ethanol. Evaporate the ether extract (filtered if traces of suspended matter are present) in a tared flask. When all but 5 to 10 ml. of the ether has boiled away blow off the remainder with a slow stream of hydrogen (or oxygen-free nitrogen or carbon dioxide), add 2 to 3ml. of ethanol (or pure acetone) and continue the gas stream until all the solvent is removed.Do not leave the flask on the water-bath beyond this point. Cool and weigh. Dissolve the unsaponifiable matter in light petroleum and make up to 50 ml. in a measuring flask. The solution is then ready for chromatography and incidentally should be used without delay because solutions a few hours old are often difficult to chromatograph-a phenomenon probably connected with the observation that such solutions develop a slight cloudiness. It may be of interest to use a portion for determination of Ei& 326 mp calculated in terms of the original oil. (The diluent for this should be cyclohexane and the E value can be quoted as “in cyclohexane,” for the presence of a small quantity of light petroleum is immaterial). This E “via unsap.” may be up to 30 per cent.lower than the gross E value. The chromatographic column (Fig. 1) consists of a glass tube about 45 cm. long and of 6 to 7 mrn. internal diameter drawn out and plugged with cotton-wool at one end. A wider tube 50 cm. long and of 12 mm. internal diameter is sealed to the top end of the column. The alumina should be of such an activity that 0.4g. of whale-liver oil unsaponifiable matter deposited on a column of log. of alumina as described below and developed with sufficient light petroleum to make the total volume of solvent 50ml. forms the first main (yellow) zone about half-way down the column. The aluminas commonly sold for chromato-graphic work (e.g. 100 to 200 mesh “Activated Alumina” ex Peter Spence and “Aluminium Oxide Standardised for Adsorption Analysis according to Brockmann” ex Savory & Moore) are usually too active for the purpose.Both the brands mentioned should be heated for six hours at 800” C . and afterwards exposed in a thin layer to the atmosphere overnight; the product will be found to have the correct activity. If the zone does not form properly or if it diffuses down the column the most likely explanation is that the acetone has not been completely removed from the unsaponifiable matter. A new preparation should be made. To prepare the column for chromatography it is set vertically in a stand closed at the bottom with rubber tubing and spring clip and filled with light petroleum to within a few cms. of the top of the wide tube. Ten g. of alumina are poured through a small funnel and allowed to settle.The solvent is driven through under a pressure of 20 to 25 cm. of mercury-air is safe to use although nitrogen hydrogen or carbon dioxide may be more convenient. When the solvent surface has sunk to within 1 to 2 cm. above the top of the alumina the column is ready to receive the solution of the unsaponifiable matter. A quantity of the light petroleum solution containing 0-35 to 0.4g. of unsaponifiable matter is pipetted on to the remaining i to 2ml. of solvent in the column and the great care. The recommended method is this 664 GRIDGEMAN GIBSON AND SAVAGE CHROMATOGRAPHIC ESTIMATION [VOI. 73 pressure redapplied. When all but 1 to 2ml. of the solution has passed into the alumina, enough fresh solvent is added to bring the total volume to 60 ml.Pressure having again forced the surface down to within 1 to 2 cm. above the alumina 25 ml. of a 96 4 mixture of light petroleum and ether is poured in. When under pressure this has almost disappeared into the alumina 26 ml. of a 92 8 mixture is added. And so on. Each addition must contain 4 per cent. more ether than its predecessor; pressure must be continually applied (except of course while fresh solvent is being added) ; and it is important that the solvent surface should never be allowed to disappear into the alumina otherwise air will be pushed into the hromatogram and oxidation may ensue. 10 AIR RESERVOIR OR INERT-GAS CYLINDER. f t2mm. DIA . -COTTW-WOOL PLUG. -7 Fig. 1 K ITOL VITAMIN A OXIDIZED MAYERIAL BROWN 6ROWN-V'ELLOW ORANGE BROWN I Fig.2 During the process the chromatogram will be seen developing. The least adsorptive fraction anhydro-vitamin A (a biologically inert hydrocarbon) passes down the column without visible zoning and its appearance in the eluate can be detected by Carr - Price spot test-it gives a blue reaction similar in shade t o that of vitamin A itself. The amount of anhydro-vitamin A is usually small. The lowest visibly adsorbing zone is oxidised material. The appearance of a typical chromatogram when the anhydro-vitamin A is just beginning to come through is shown in Fig. 2 (for further details of which see next section). The eluate is collected in 6-ml. fractions in small marked test tubes. Collection need not normall December 19483 OF VITAMIN A IN WHALE-LIVER OIL 6% begin until the first visible zone (oxidised vitamin A) has almost left the column but until the operator is familiar with the process it is advisable to begin earlier.The vitamin A should lie between the “oxidised” zone and the kitol (yellow-brown) zone; it is much paler than the other zones being often almost invisible. a I! s I I I I “\ I L I O 4-A few drops of solution from individual tubes are tested with Cam- Price reagent to establish the range of tubes containing the vitamin. The tubes corresponding to the zone below the vitamin A usually give a reddish-purple colour with the reagent; while those corresponding to the zone above the vitamin give a bluish-purple or greenish-purple colour. Both these colours are readily distinguished from the bright blue of the vitamin-A solution.Moreover in a good chromatogram the set of vitamin-A tubes will be separated at either end from the sets containing the adjacent zones by one or two tubes whose eluate content is almost nil; these correspond to the inter-zone regions in the chromatogram and will give only a faint coloration with the Carr Price reagent. Aliquots drawn from those tubes showing a positive reaction for vitamin A are pooled and diluted with cyclohexane to the strength appropriated to the spectrophotometer on which E values are to be measured. A photo-electric instrument is preferable to the photographic type because of the desirability of obtaining a detailed absorption curve between 256 mp and 375mp of the vitamin-A fraction’ (Stronger solutions will be required for accurate determination of the lower optical densities at these extreme wave-€engths).If the fraction is pure the maximum of the absorption curve will lie between 326 mp and 328 mp and E 300 mp/EAmax. will be not more than 0.63 and E 360 mp/EA,,. not more than 0.35. FULL ANALYSIS OF THE ULTRA-VIOLET ABSORBING CONSTITUENTS OF A SAMPLE OF WHALE-LIVER OIL A sample of poor quality whale-liver oil exhibiting A,, 284 mp was chosen for detailed analysis of the unsaponifiable constituents contributing ta the observed E:& 326 mp value of 20.4 on the whole oil. The acetone-insoluble fraction was similarly examined 666 GRIDGEMAN GIBSON AND SAVAGE CHROMATOGRAPHIC ESTIMATiON [YOl. 73 UNSAPONIFIABLE CONSTITUENTS-The unsaponifiable matter from 5g.of the oil was prepared as described above; the product weighed 0.85 g. and showed Et& 326 mp calculated in terms 6f the whole oil of 14.4. For chromatography 0.38 g. of the unsaponifiable matter was dissolved in 20 ml. of light petroleum. Development and elution of the chromatogram were carried out with the following solvents : (1) 30 ml. light petroleum. (2) 25 , 4 per cent. ether in light petroleum. (3) 25 9 ) ) 9 J # 9 ) 9 9 ) ) 9 , (6) 25 # # 2o # ? 9 ) J # # 9 J J 9 , (7) 25 #P 24 # 9 J t 1 ) 9 ) # # Y, (8) 25 8 ) 48 J J 9 J # # # # P 9 9 (4) 25 P 9 J J # 9 3 ) 9 ) J 9 I , (5) 25 $ 9 J ) 9 9 1 ) J I # t 9 (9) 15 , ether. (10) 25 , absolute ethanol. The use of 48 per cent. and 100 per cent. ether and finally of ethanol is normally unnecessary, as all the vitamin A is eluted by the less polar mixtures but on this occasion complete stripping of the column was required to show the absorptive make-up of the whole of the unsaponifiable matter.Collection of the eluate began during the percolation of the first mixed solvent (No. 2 above) and when the chromatogram had developed to the extent shown in Fig. 2. Fractions 1 and 2 i.e. the first 50 ml. of eluate and the following 30 ml. were collected in bulk the demarcation line between them being approximated at the point where spot tests showed the Carr - Price colour to be changing from blue (indicative of anhydro-vitamin A) to purple (indicatite of oxidised vitamin A). The second fraction was ended when the lowest visible (yellowish) zone had descended almost to the bottom of the column; collection in 5 ml.portions then began and continued until 34 such portions had been taken off in marked tubes. This was supererogatory so far as the isolation of the vitamin A is concerned as the 20th tube was the last to give the characteristic Carr- Price reaction but the extra portions were collected in order to isolate the kitol fraction. By the time the 34th tube had been reached the eluting solvent was 100 per cent. ether and all the main zones had been removed. There remained the topmost brown zone which was stripped into 45 ml. with ethanol. The 34 tubes of eluate were grouped into four lots on the basis of Cam - Price spot tests. Details are given in the Table below which contains the essential data on all seven fractions.Cam - Rice test Quantity (SbCI in Predominant E 2. Fraction (as eluate) CHCl,) Amax. constituent 326 mp. 1 50 ml. Blue 350 367 and Anhydro-389 mp. vitamin A 1.69 2 30 ml. purple Faint c }Z-yJ { 0*05 materials 0.31 3 11 x 5 ml. Dull gref-blue c 4 9 x 6 ml. Deep blue 326 mp. Vitamin A 7-37 5 11 x 5 ml. Green to 290 mC1 Kitol 2-84 Purple - 0-34 6 3 x 5ml. Pale blue -7 45 ml. - - - 0-36 Total 12-86 2V.B.-(i) Fractions are in order of increasing adsorbability. (ii) The B values in the last column are calculated oa the original whole oil. The total E:& 326 mp value accounted for is 12.9; this compares with the value of 14-4 on the unsaponifiable matter before chromatography. The absorption curves of the fractions, and a comparison of their summation with the obsmed curve of the unsaponifiable matter, are shown in Fig.+for convenience the curves of fractions 2,3,6 and 7 have been combined December 19481 OF VITAMIX A I S WHALE-LIVER OIL 667 .~ETONE-INSOLUBLE FRACTIONS-A 5 g. sample of the original whale-liver oil was extracted with three 30-ml. portions of acetone; each extraction comprised boiling for 16 minutes followed by overnight cooling in a refrigerator. The residual insoluble material predominantly phosphatides was freed from solvent and taken up in cyclohexane. Spectrophotometric examination of the solution yielded the absorption curve shown in Fig. 4 where also the summation of this curve with that of the unsaponifiable fraction is compared with the absorption curve of the original oil.At 326 nip the EiE. value of the acetone-insoluble fraction is 4.6 (calculated on the original oil)-which accounts for about three-quarters of the observed difference between the corresponding direct (20.4) and “via unsap.” (14.4) values on the original oil. The acetone-insoluble fraction is mainly phospha-tides; nevertheless it would be presumptuous to attribute the observed absorption to these compounds which are normally pretty transparent in this region ; other associated compounds are more likely to be responsible. Identification has not been attempted. DISCUSSION Although the method was developed specially for the analysis of an unusually complex material it can obviously be extended to more normal oils. Chromatography of the unsaponi-fiable matter of fish-liver oils carried out under the conditions described above usually pro-ceeds satisfactorily and the E:Z 326 mp.values of the fractions add up to almost 100 per cent. of the expected value. We have in this way analysed a shark-liver oil a mixed fishdliver oil diluted in vegetable oil a distilled vitamin-A ester concentrate and a cod-liver oil. Of the total absorptions at 326 mp. (on the whole oil for the first three samples and “via unsa ., for the cod-liver oil) the following fractions were found to be due to vitamin A 85 92 and 90 per cent. respectively. Some confidence that these results and those of whale-liver oil analyses are of the right order has been derived from recovery tests in which vitamin-A acetate was dissolved in vegetable oi€ and on another occasion in dolphin oil (a sterol-rich, vitamin-A free material) recoLferies of 97 to 99 per cent.were obtained on chromatography of the unsaponifiable fractions. It may be noted that the vitamin-A fractions chromato-graphically isolated from whale-liver oils various fish-liver oils aad concentrates and solutions of vitamin-A acetate exhibit indistinguishable ultraviolet absorption curves. The translation of E:Z. 326 mp. obtained by the chromatographic method to the conventional I.U. per gram deserves comment. The conversion factor customarily used for fish-liver oils and concentrates is 1600. As these materials have up to 10 per cent. of irrelevant absorption at 326 m p it would be inappropriate to apply the same factor to “pure” curves. Following Morton and Stubbsa we would recommend E:;ib.326mp. x 1800 for fractians whose purity is not in doubt. On the assumption that pure vitamin-A alcohol exhibits E:E. 326 mp. = 1700 in cyclohexane this is tantamount to taking the Internationd Unit as 111700 x 1800 i.e. 0.326 microgram. A value of this order has indeed been implicit in all vitamin-A analysis to date. (It is sometimes suggested that the time is approaching to express vitamin-A analyses in percentage but this method has the serious disadvantage of breaking with a well-establish convention. Moreover as the effective International Unit is really a weight of the vitamin there is no logical objection to its retention). The criterion for “fractions whose purity is not in doubt” is not easily defined. As already stated we regard curves as “pure” if their ordinates at 300 mp.and 360 mp. are not more than 63 per cent. and not more than 35 per cent, respectively of that at 326mp. (assuming this to be A,,,,,.; it is not always easy to say whether the peak of the curve is at 326 327 or 328 mp.-and occasionally it is clearly 328 mp.). If values substantially greater than these are obtained (such cases are rare) the best advice is repeat the analysis. A makeshift solution would be to accept the curve and to use a lower conversion factor-say 1600. Another device is to “ correct ” the curve trigonometrically for irrelevant absorption as described by Morton and Stubbs,7,8 but for several reasons we hesitate to adopt this procedure. First the assumption of “effective linearity’’ (for which there is no a eriori evidence) of the irrelevant absoprtion at the three selected wave-lengths is very exacting; even slight curvilinearity upsets the correction.Secondly the correction magnifies observa-tional errors (at Amax. the magnification is seven times). Thirdly-and this is an observation that links with the other more theoretical reasons-curves can be obtained that after three-point corrections yield E values higher than the originals 668 GRIDGEMAN GIBSOS AND SAVAGE VITAMIN -4 [Vol. 73 SUMMARY Chromatography on weakly adsorbing alumina of the unsaponifiable matter of whale-liver oil develops well-defined zones that can be eluted seriatim with polar solvents. One zone consists of vitamin A only; it can be collected and assayed spectropkotometrically.We are glad to avail ourselves of this opportunity of acknowledging the help at various stages of the work of Dr. J. R. Edisbury Miss L. G. Jagger and Messrs. D. D. Penketh, R. J. Taylor and M. Trotter. REFERENCES 1. Morgan R. S. Edisbury J. R. and Morton K. A. Biocketn. J. 1936,29 1646. 2. Drummond J. C. and Haines R. T. M. ANALYST 1938 63 335. 3. Willstaedt H. and Jenson H. B. R’ature 1939 143 474. 4. Kringstad H. and Lie J. Tidsskr. h‘jerni Berge,. 1941 1 83. 5. Pritchard H. Wilkinson H. Edisbury J. R. and Morton R. A. Biocherti. J. 1935 31 258. 6. Embree K. D. and Shaatz E. M. J. Atner Chew. SOC. 1943,65 910. 7. Morton R. A. and Stubbs A. L. ANALYST 1946,71 348. 8. - - Biochem. J . 1948 42 1%. RESEARCH DEPARTMENT LEVER BROTHERS & UNILEVER LIMITEI3 PORT SUNLIGHT CHESHIRE DISCUSSION J m e 1948 Dr.W. F. ELVIDCE said that thanks to the author’s generosity he had had an advance copy of their paper some twelve months ago and had had the opportunity of using the method in a number of cases only one of which however was a mammalian liver-oil concentrate. He and his colleagues were particularly interested in obtaining atxurate values for vitamin A on oils extracted from various pharmaceutical prepara-tions with which in many instances abnormal absorption curves were obtained. These abnormalities were thought to be due to extraneous absorption from two sources first from oxidation products of the oil itself and secondly from extraneous material derived from the vehicle and flavouring etc. They used two methods to try to correct for or eliminate this extraneous absorption the first based on Morton and Stubbs’s correc-tion method and the other on Gridgeman’s chromatographic method.They had found the latter extremely useful and the purified material resulting from it corresponded very well with the data given by Morton and Stubbs for pure vitamin-A alcohol and needed very little correction by their (Morton and Stubbs’s) method. He hoped that the author’s method would soon be published in THE ANALYST. MR. GRIDGEMAN said he was glad to hear that Dr. Elvidge had successfully used the method for a variety of vitamin-A preparations because he and his colleagues were themselves finding it widely applicable outside the province of whale-liver oil. I t was worth noting in this connection that if the unsaponifiable matter prepared from say a fish-liver oil amounted to less than 0.35 g.it was advisable to make up the weight with cholesterol. Professor R. A. MORTON said that through the courtesy of Messrs. Lever Brothers Unilever Ltd., he and his colleagues had been kept informed of the development of this analytical method. Dr. A. L. Stubbs and he were given every assistance in trying it out and they found it much better than any earlier method, Dr. R. K. Barua had been working in his (Dr. Morton’s) laboratory on whale-liver oil for the past two years one of his objectives being the isolation of natural kitol esters. He had developed a chromatographic procedure for separating vitamin-A esters from kitol esters and out of it had grown an analytical method which gives results agreeing closely with those obtained by the method just explained and having advantages in ease and convenience since it was not necessary to prepare the unsaponifiable fraction. Dr. Morton gave an outline of ’the method and said that a fuller account of the work would be published elsewhere. Professor T. P. HILDITCH asked Mr. Gridgeman if the removal of v’itamin A from the column was quantitative and easy to carry out. Mr. GRIDGEMAN said that all the evidence indicated that removal was quantitative; the demarcation of the collection tubes containing vitamin A was clear-cut and the reproducibility of the results was high. As to ease of operation care had of course to be exercised but there were no special difficulties. Mr. SAVAGE drew attention to two precautions against vitamin-A loss first the ensuring that the head of the alumina column was a t no time exposed to the air during chromatography; secondly the avoidance of ouer-dry alumina. The moisture content of the alumina used has been about 2 per cent

ISSN:0003-2654    

DOI:10.1039/AN9487300662

出版商:RSC    

年代:1948

数据来源: RSC

摘要:

426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively.Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE.By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time.The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction

ISSN:0003-2654    

DOI:10.1039/AN9487300669

出版商:RSC    

年代:1948

数据来源: RSC

摘要:

426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively.Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE.By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time.The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction

ISSN:0003-2654    

DOI:10.1039/AN9487300671

出版商:RSC    

年代:1948

数据来源: RSC

摘要:

426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents.It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate.There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international.The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively.Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited.The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation.Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE.By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years. The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr.Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion. The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies.Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on. Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time.The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice.Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction426 REVIEWS INKS : THEIR COMPOSITION AND MANUFACTURE. By C. AINSWORTH MITCHELL, D.Sc., F.I.C. Fourth Edition. Pp. xi + 408. London: Charles Grihn tt Co., Ltd. 1937. Price 12s. 6d. net. This, the fourth edition of the standard and, indeed, so far as the reviewer’s knowledge goes, the only text-book on the subject in the language, bridges L gap of 13 years.The author, pre-eminent in his particular sphere, needs little more introduction to the world of technical industry than he does in his official capicity to readers of THE ANALYST, while his reputation in forensic science in all that appertains to handwriting is international. The chemistry of ink, difficult as it is and at times not a little obscure, hcl- riot developed markedly in the interval since 1924; but what progress has been made is covered by Dr. Mitchell in this edition in a very thorough manner. He has found it necessary to enlarge his work to the extent of some 20 per cent. and, in addition, to rewrite a large portion.The arrangement of the book follows the lines of previous editions. After a comprehensive historical introduction, the work is divided into three sections dealing with writing inks, printing inks, and inks for miscellaneous purposes, respectively. Under Section 1 are considered the chemical nature and treatment of the various raw materials used for writing inks from lcmp black to galls, the composition of finished iron-gall, logwood, vanadium, aniline black, and coloured inks, as well as a comprehensive scheme €or the tech~ical examination of inks, handwriting specimens and the identification of forge:-ies. Section 2 deals with the manufacture and examination of printing inks. ,tnd Section 3 with the miscellaneous materials entering into the compositilxx of copying, marking, safety, sympathetic, typewriter inks and so on.Amongst new matter may be noted references to the use of lignone sulphni--,ites in connection with writing ink, a scheme for the identification of individual con- stituents in inks in the form of writing, and the application of filtered ultra-.& if )let light and of infra-red photography in the elucidation of those problems to which such methods are suited. The British Government Standard Specificatior:s for Writing Inks, revised in 1928, are included for the first time. The avaihble evidence upon the constitution of gallotannin is brought up to date and <tbly reviewed, and there is a Comprehensive list of British patents. It is as difficult to withhold admiration of the encyclopaedic scope cjf the matter and references in this book as it is of the erudition and industry displiiyed in its compilation. Practically nothing that comes to mind has escaped atterition, and it is with rather impish glee that the reviewer, after careful search, asserts that he finds no specific reference to the type of alkaline (ammoniacal) gallotannate- iron ink, said t o find favour in the United States, although the di-ammonium hydroxyferrigallate compound of Silbermann and Ozorovitz receives notice. Nor is there mention of that class of quick-drying writing fluids which depend for their efficiency upon partial destruction of the paper sizing by caustic alk 1.5 or sodium silicate. There is no evidence that lignone sulphonate inks have proved se-rious competitors to iron-gall writing inks (pp. 15 and 175). Apart from the unkttmwn quantity of permanence, the principal failing of this type lies in their liability to contain traces of free sulphurous acid to which suspicion attaches in connt-ction

ISSN:0003-2654    

DOI:10.1039/AN9487300674

出版商:RSC    

年代:1948

数据来源: RSC