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 SEPTEMBER, 1947 Vol. 72, No. 858 THE ANALYST PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS AND OTHER ANALYTICAL CHEMISTS Fluorimetric Analysis The following four papers were read at a meeting of the Physical Methods Group in London, on February llth, 1947.Fluorimeter Design BY E. J. BOWEN THE first consideration relating to fluorimeter design is whether the measurements should be by eye or by photo-cell. Visual measurements suffer from all the weaknesses of the human observer, while photo-electric methods can be carried out more accurately and rapidly, and with less fatigue. There are occasions, however, when visual methods may be preferred, if the solution contains unextracted impurities themselves fluorescing with a different colour. Changes of tint of the fluorescence then give warning that there is something unsatisfactory about the solutions. Instruments for visual work are the Pulfrich Photometer or adapted plunger- type colorime ters . In photo-cell instruments the lamp, solution cell, and yhoto-cell may all be arranged in line, or the photo-cell may be arranged to collect the fluorescent light emerging at right angles to the exciting light beam.The latter arrangement seems preferable, as for very weak fluorescences it may not be possible to remove by filters all traces of the direct exciting light beam. In the right-angled arrangement up to four photo-cells could be used round the solution cell, though in practice two would probably be the optimum. For very accurate work it is desirable to eliminate the effects of fluctuations in the intensity of the exciting-light source. This is most conveniently done by using a double apparatus to allow of balancing. Light Such an arrangement is illustrated in Fig.1. P 0 9 P Fig. 1. See Umberger and Lamer, J . Awtev. Chem. SOC., 1945, 67, 11. from a central lamy L sends out two beams in opposite directions; these are made parallel by lenses and of appropriate wavelength by light-filters Fl. After passing diaphragms D, the beams traverse solution cells C . One cell contains a standard and the other the solution to be measured. These need not be solutions of the same substance if standards more stable than the solutions to be measured are better. The fluorescent light passes diaphragms D, and filters F, to reach photo-cells P. The photo-cell outputs are connected in opposition to a measuring device balanced to zero when identical solutions are placed in the cells C. 377 Fluoriineter viewed from above.378 BOWEN : FLUORIMETER DESIGN [Vol.72 The following considerations relate to the various components. Lamp-For most work the small high-pressure 125-watt mercury lamp is the best, since high-intensity monochromatic light, and long-wave ultra-violet light, are easily obtained from it. To avoid inconstancy of output the lamp should be provided with a stabilised voltage and guarded against irregular ventilation, since of the three lamp variables, voltage, current and temperature, only two are independent. It may happen that the absorption band of a fluorescent solution, as of rubrene in hexane, lies in a region where the mercury lamp provides no line. A concentrated filament projection- type tungsten-filament lamp must then be used. This needs a copper sulphate solution filter to remove heat from the light beam and some care in design to dissipate the great heat in the lamp housing.Filters F,-For measurements at low concentrations the filters Fl should transmit a spectral region more or less coincident with a high or a maximum value of the absorption band of the solution. Using the mercury lamp it is roughly true that colourless solutions (even when concentrated) need the 3650 A. line, and yellow solutions the 4358 A. line. The presence of nitrites, sulphites, and other light-absorbing substances in the solution may render the use of the 3650 A. line impossible even though it may fit best the absorption band of the fluorescent substance. In some circumstances the mercury line 4047 A. might be very useful, but it is not easy to isolate at high intensity.Gelatin-film (between glass) filters are commonly used because they can be obtained in a greater range than coloured glass filters. When exposed to the full radiation of the mercury lamp, however, they may show rapid deterioration. It is very desirable to interpose an ultra-violet absorbing glass filter such as Chance OY9 or 10 to minimise this trouble. SoZution cells-Given sufficiently sensitive detecting inst rumen ts, the ultimate sensi tivi ty of fluorimetry is set by five factors: (a) Rayleigh and Raman scattering from the liquid. (b) Scattering from dust particles. (c) Scattered light from reflections from the cell walls. (a) Fluorescence of the solvent. (e) Fluorescence of the cell walls. Present-day sensitivities are so far from the limit set by (a) that this may be left out of consideration. Factors (b) and (d) can be minimised by careful purification and technique. Factor (c) is a matter of careful choice of material.Glass fluoresces owing to the presence of traces of certain elements such as manganese, cerium, samarium or europium, and the production of “non-fluorescent ” glass needs the co-operation of the glass manufacturers. Scattered light from the cell walls is probably the largest source of error in most instruments. The following devices would reduce this trouble. (a) The use of a cell shaped like a cross as shown in Fig. 2, constructed of opaque material with four clear plane faces. (b) Scrupulous care in avoiding surface contamination and scratches in the conventional type of rectangular cell.(c) Careful adjustment of lenses and of diaphragms D, to limit the path of the light- beam to the centre part of cell C. (a) The use of very thick glass ends to the cell C on the exciting light axis, or, alter- natively, impersion of C in a larger rectangular trough containing a liquid, so that the light-scattering planes where the exciting light enters and leaves the solution are kept well away from being “viewed” by the photo-cell at P. Balancing of @zoto-ceZZs-There are various ways of balancing the photo-cells and of obtaining a measure of the fluorescence. The reading may be taken either directly from the opposed photo-cell outputs when unknown and standard solutions are placed one in each of the cells C, or the detecting instrument in the photo-cell circuit may be brought to zero by adjusting (a) a variable calibrated diaphragm in a D, position, or (b) a variable and graduated resistance or potentiometer in the electrical circuit.The relative merits of these methods have never been fully assessed. Filters F,--These may be gelatin-film filters chosen to transmit the fluorescent light while removing the exciting wavelengths. Were these 100 per cent. efficient, errors due to scattered exciting light would disappear. There is usually need to off-set loss of light by using not very dense filters.Sept., 19471 BOWEN : FLUORESCENCE QUENCHING IN SOLUTIONS 379 Photo-cells-The barrier-layer type of photo-cells has the advantage of not needing an external source of electrical supply. They are not sensitive enough, however, for work with ieebly fluorescent solutions. Vacuum-type alkali-metal cells, chosen for the wavelength range of the fluorescence to be studied (Le., potassium for blue and green, rubidium for orange, and caesium for red) are then necessary. Their outputs are amplified, either by the D.C. method with an electrometer valve (preferably enclosed with photo-cell and high resistance TO PHOTO- 1 CELL Fig. 2. in an evacuated glass envelope) or by A.C. methods with light-choppers interposed in the light beam. A new development, however, is now on the way. Nine-stage photo-electron multipliers, such as the American R.C.A. tube 931 A, provide exceedingly high sensitivities to light over the whole spectral range, and are capable of measuring to 10-7 foot-candles or less. Used with a spectrometer they permit the direct measurement of Raman lines from liquids which need quite.long exposures of a photographic plate. As it is very desirable to cut down the intensity of the exciting light beam to avoid photochemical changes in unstable solutions, these new detectors will provide greater sensitivity with lessened risk of destruction of fluorescent material. One may even forecast a fluorimeter of the future with a spectrometer interposed between the solution and the multiplier cell, whereby both the intensity and the wavelength distribution of a feeble fluorescence may be simultaneously determined. PHYSICAL CHEMISTRY LABORATORY OXFORD