172 PARTICLE-SIZE ANALYSIS [Proc. SOC. Analyt. Chem. Particle-size Analysis The following are summaries of papers presented at the Joint Meeting of the Midlands Section with the Particle Size Analysis Group held on June Sth 1966 and reported in the September issue of Proceedings (p. 139). The Perkin-Elmer - Shell Sorptometer By G. A. LOMBARD (Geigy ( U. K.) Ltd. Pigments Division Simonsway Manchester 22) MR. LOMBARD said that the Sorptometer was a commercial instrument designed to measure the surface area of solids by dynamic adsorption. The principle of the method was to pass a known mixture of adsorbent (nitrogen) and carrier gas (helium) over the sample and to detect changes in concentration of nitrogen in the helium due to adsorption or desorption by means of a thermal conductivity bridge with an amplified output to a potentiometric recorder.The areas of the peaks produced were proportional to the amount of gas adsorbed at the particular partial pressure. Four models had appeared to date and measurements on a model 212B instrument have been made of a range of organic pigments with surface areas in the range 7 to 100 sq. m per g. Results showed that the standard of accuracy and reproducibility was adequate for most purposes and calculation of relative standard deviations gave values between 1.1 and 3.6 per cent. which were of comparable order to those published in the literature for the commercial instrument. Satisfactory agreement was found with results obtained from November 19661 PARTICLE-SIZE ANALYSIS 173 measurements on a conventional volumetric static apparatus.It was felt that the use of elevated temperatures for pre-treatment of the sample before measurement by de-gassing on a high vacuum line might well be best avoided as a general feature for organic pigments and that helium streaming was likely to be a lengthy procedure. De-gassing on a high vacuum line at room temperature for 2 hours seemed to be suitable and for this operation it was felt that the important point was to reach some satisfactory final pressure. Five-point measurements took 2 to 3 hours after the instrument was ready for the first adsorption; three-point measurements 14 to 2 hours; and single-point measurements 25 to 30 minutes (all times were exclusive of calculation). Peak areas could be measured either by a planimeter or by an integrator such as a Kent Chromolog unit in which event the surface area value could be obtained from the results of three-point measurement within 30 minutes of completing a run.With such a unit it was possible to make 2 five-point measurements in a normal working day or 3 to 4 three-point measurements the latter depending on the time taken for adsorption and desorption. In the absence of an integrator the method was probably only slightly quicker than the static method but the great advantage was that adsorption was not measured under high vacuum. The instrument was constructed from metal components fragile glassware being completely absent except for a sample tube and flow-meter. It was therefore much more robust and the method certainly more convenient and more suited to routine or semi-routine determination.Operators needed to be only of average dexterity and to take normal care to use the instrument satisfactorily. It had to be remembered that the @/Po range could not be covered completely and this might limit the use of the Sorptometer in drawing a full isotherm. The Numinco - Orr Surface Area - Pore Volume Analyser By A. G. COTTRELL (Imfievial Chemical Industries Ltd. Mond Division Runcorn Heath Cheshire) MR. COTTRELL described the Numinco - Orr surface area - pore volume analyser that was designed by Professor C. Orr in conjunction with the Numec Instrument Company of Pennsylvania. The Numinco instrument was an instrumental version of the well known glass BET apparatus. It consisted essentially of- (i) a seven-valve stainless-steel manifold through which three sample holders were (ii) an evacuation system consisting of a cold trap a diffusion pump and a mechanical (iii) a sensitive Bowden tube type pressure indicator; (iv) two alternative extra volume bulbs which could be included in the manifold when (v) a thermistor low pressure detector; and (vi) inlets for the gases helium and adsorbate which could be nitrogen krypton argon The thermistor pressure gauge was used to measure both the de-gassing pressure during evacuation and the adsorption pressure of krypton during a surface area test.The system was shifted from one purpose to the other by setting a switch on either “DE-GAS” or “TEST.” A re-settable timer was incorporated into this instrument to indicate how long a sample had been exposed to a particular pressure during de-gassing. Another auxiliary component of the apparatus was a thermistor thermometer ; this operated in two ranges-one to indicate the temperature of the manifold system (22” to 37” C) the other to take the temperature of the liquid nitrogen used to cool the samples for the actual tests.Other components were heating mantles which fitted over the sample flasks so that the samples could be heated to any required temperature during de-gassing. The tempera- ture of any sample could be checked by plugging in a thermocouple lead attached to each heating mantle. interconnected ; pump ; extra adsorbate was required for high surface areas; or other gases. 174 PARTICLE-SIZE ANALYSIS [Proc. SOC. Analyt. Chew. The steps carried out for the determination of a surface area were similar to those on a normal BET apparatus except that the time-consuming pressure - volume manipulations had been considerably simplified.The de-gassing period depended on the individual sample 2 hours at 250” C being normally sufficient on a thermally stable sample. After de-gassing the “dead space” or unoccupied sample volume was measured by using helium. The nitrogen adsorption stage differed slightly from that on a glass BET apparatus in that it was advisable with the Numinco to use a constant nitrogen pressure in the manifold for each introduction and continue until the final pressure was at least 100 mm of mercury; with the BET apparatus on the other hand nitrogen was adsorbed at a series of increased pressures. The calculation of the results for any type of BET surface area was time consuming but these had been simplified to some extent by the use of calculation sheets.The final two where P8 = the second condition columns on these sheets gave values for-and pressure P = the saturation pressure i.e. the vapour pressure of the liquid nitrogen P used as the coolant V = the volume of gas adsorbed and X = -. PS could be fitted by an equation of the form- p2 P V(1 - X ) An arithmetic plot of the last two columns gave the normal BET isotherm curve which where Vm is the volume of gas required to form a mono-layer on the surface of the tested solid and C is a constant. The surface area was then calculated from the slope and intercept in the usual way. Mr. Cottrell described the use of a computer programme for obtaining the results. The programme was based on the calculation sheets and each column of values printed out in full by the computer so that the graph could be plotted if required and any unusual results investigated.By using a 15-sample de-gassing unit that was separate from the analyser about 8 BET determinations could be made in one day. The Strohlein Areameter By D. P. BRYANT (Welwyn Hall Research Association Welwyn Hevtfordshire) DR. BRYANT reviewed the Strohlein Areameter. This equipment which was constructed mainly in plastic with O-ring seals throughout was manufactured by Strohlein & Co. of Diisseldorf to a design by Haul and Dumbgen. Basically it consisted of two bulbs; one containing the sample under test was connected to a differential manometer. The operation of the apparatus depended on the low-temperature nitrogen adsorption method of Brunauer Emmett and Teller (BET) and normally only one point on the isotherm was determined.The bulb containing the powder under examination was outgassed by purging with nitrogen at elevated temperature in a separate unit. The dissociation of the outgassing and adsorption processes led to a high rate of measurement ; 16 samples per day was suggested as a possibility depending on the nature of the samples. After outgassing the sample bulb was transferred to the adsorption apparatus which was then filled with nitrogen at room tempera- ture. On cooling the sample and reference bulbs in liquid nitrogen the gas pressure in the apparatus fell to the BET region and the differential pressure on the manometer was recorded. This technique avoided the “dead-space” correction and provided increased sensitivity com- pared with conventional BET equipment.It was stated that the normal BET equation could be used to evaluate the results from a knowledge of the atmospheric and the measured differential pressures the relevant appara- tus constants being given in the instruction manual. A simplified form of calculation associ- ated with a nomogram by Gall minimised the computation required. However the simplifications introduced into the basic equation imposed certain restrictions. The principal restriction was that the preferred sample weight was that which would give a differential pressure of 150 mm which is equivalent to a sample area of 25 sq. m. For samples of low November 19661 PAPERS ACCEPTED FOR PUBLICATION 175 specific surface the volume of material present necessitated a further correction that could be calculated from the nomogram.This correction was small at the preferred sample weight and errors due to the use of incorrect densities were minimised. The lecturer reported that results obtained by this simplified method were somewhat lower than those obtained by conventional BET methods and an arbitrary correction factor of 1.05 had been included in the calculations by the manufacturer. While this was satisfactory for a wide range of materials it might be preferable to calculate afresh the correction factor in instances when a single material was being measured for routine control purposes provided that the samples were of approximately the same specific surface. Some results illustrating the effect of sample weight on measured surface area of titanium dioxide were shown to follow the expected trend due to pressure errors of the differential manometer.However the scatter of results at this preferred pressure suggested that the deviations at maximum and minimum sample areas (50 and 7 sq. m respectively) were within the over-all range of experimental error. The speaker concluded with some suggestions for other adsorbate - coolant combinations. Papers Accepted for Publication in The Analyst THE following papers have been accepted for publication in The Analyst and are expected to appear in the near future. “The Determination of Boron in Fertilisers,” by H. Borland I. A. Brownlie and P. T. Godden. “A Rapid Infrared Spectrophotometric Method for the Analyses of pp’-DDT in Formulations of Technical DDT,” by D. J. Hamilton and T.J. Beckman. “Inorganic Thin-layer Chromatography Part 11. Chromatography of Some First Row Transition Metals on Thin-layers of Substrates Impregnated with Tributyl Phosphate (TBP),” by L. S. Bark G. Duncan and J. T. Graham. “A Simple Low Cost Gas Chromatograph for the Determination of Fatty Acids,” by B. H. Priscott. “The Determination of Trace Amounts of Chloride by Rapid Evolution - Conductimetric Procedure,” by B. H. Priscott. “Separation of Mustard Gas and Hydroxy Analogues by Thin-layer Chromatography,” by F. G. Stanford. “Spectrophotometric Determination of Aluminium in Soil Extracts with Xylenol Orange,” by D. T. Pritchard. “The Amperometric Titration of Submillinormal Concentrations of Hexacyanoferrate (111) with Mercury (I) Perchlorate,” by J. T. Stock and R. J. Merrer.“A Review of Techniques in Gas Chromatography Part 1 Choice of Solid Supports,’’ by E. A. Walker. “The Determination of Calcium in Biological Samples by X-ray Fluorescence,” by K. P. Champion and R. N. Whittem. “An X-ray Spectrographic Method for Determining Barium,’’ by E. R. McCartney and S. A. Prokopovich. “Analytical Application of a O-5-MeV Cockcroft - Walton Set. Based on the Measurement of Prompt y-Radiation,” by T. B. Pierce P. F. Peck and D. R. A. Cuff. “The Determination of Dicumyl Peroxide in Polystyrene Materials,” by J. A. Brammer S. Frost and V. W. Reid. “The Component of Commercial Titan Yellow Most Reactive towards Magnesium Its Isolation and Use in Determining Magnesium in Silicate Minerals,” by H. G. C. King and G. Pruden. “The Collection of Uranium(V1) on Cellulose Phosphate,” by T. Bruce and R. W. Ashley. “A Rapid Method for Determining Nitrogen in Uranium Nitrides,” by B. L. Taylor “The Determination of Warfarin in Animal Relicta,” by F. B. Fishwick and A. Taylor. and B. S. Perrett.