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An automatic changer for liquid samples
FIG. 1. Autoradiogram of writing in methyl violet ink, after treatment with silver nitrate solution labelled with Ag n°. Age of main text, 1.5 years; age of added figures (5 and 6, using the same ink), 1 month.
(a)
(b)
FIo. 2. (a) Photograph of writing in methylene blue ink (two central figures of each line) and in "Ts" brand methylene blue ink (first and last figure of each line). (b) Autoradiogram of the same specimen after treatment with potassium ferrocyanide solution labelled with C 14.
138
Technical notes formed by dissolving, respectively, zinc sulphate in an excess of potassium thiocyanate, thallous sulphate in potassium bromide and cadmium sulphate in sodium iodide. I n conformance with the Fajans-Paneth rule, the anions that give the least soluble compounds with the dyestuffs are the most strongly adsorbed and therefore yield the most distinct autoradiograms. This enables inks to be differentiated, and later additions to be detected. For example, writing in blue ink prepared from "Ts" brand methylene blue adsorbs ferrocyanide ions more strongly than writing in ink containing an ordinary methylene blue dyestuff. This is clearly seen in Fig. 2. The paper itself also adsorbs radioactive isotopes, especially if the latter are inthe form of cations. Third grade writing paper adsorbs the ions less strongly than top and second grade paper of the same kind. Sized paper with large amounts of filler adsorbs silver ions to such an extent that ink marks are with great difficulty distinguished from the general background of the autoradiogram. The marks made by graphite pencils, graphite copying pencils and coloured pencils also adsorb radioactive isotopes. In the case of pencil marks containing basic dyestuffs, adsorption is due to the latter, and age-dependence is not always observed. Acid dyes present in a pencil mark (e.g. eosin) adsorb almost exclusively only anions. Soft graphite pencil marks containing more graphite and lampblack, adsorb actions better than marks made by hard pencils. Printing ink also adsorbs silver and thallium ions. This radioisotopic method makes it possible in certain cases to prepare more distinct photographic copies of poorly legible documents, and to detect additions made in a different writing medium or at a different time. B. E. GORDON V. K. LISICHENKO
Reference 1. MEZGER 0 . , RALL H. and HE,~ss W. Angew. Chem. 44, 645 (1931).
An Automatic Changer for Liquid Samples IN radiochemical and radiomedical work the yactivity of liquid samples is usually determined with the aid of a well-type NaI-scintillation counter. If large numbers of samples must be dealt with, manual handling of test-tubes and lead shielding becomes tedious and time consuming. In order to
139
eliminate this labour automatic changers for well-type counters have been developed. ~lm In this note another instrument of this kind is briefly described, which can handle up to 50 samples. In radiochemical work the changer can simultaneously be used as a fraction collector, e.g. in combination with an ionexchange column. Fig. 1 shows a photograph of the instrument, Fig. 2 gives a schematic cross-section. Fifty polythene tubes can be placed in slots of a Perspex disk K. This disk ,turns through one position each time a tube is changed. After the disk has turned gripper G (Fig. 2) actuated by gripper magnet M picks up a tube. Then the carriage F together with tube T which contains the gripper mechanism moves to the right (in Fig. 2) so that the test-tube is brought outside the perimeter of the disk. When the carriage has reached its extreme position the test-tube is lowered into the well-counter by a motor Mx, which moves tube T vertically. Apart from the gripper and its magnet, T contains a lead-filled section L which just closes a hole in the lead shield of the well-counter, when T is all the way down. Counting is started automatically as soon as the test-tube has reached its bottom position. After a predetermined count (or time) the scaler stops and prints elapsed time (or number of counts). Simultaneously the changer is started; the test-tube is taken up and replaced in its slot in the Perspex disk. The disk then turns to the next position and so on. The horizontal movement of the carriage F and the turning of the disk are accomplished by a motor Mm The sequence of the actions is determined by 6 microswitches S1-Ss that switch the motors and the gripper magnet through a system of relays contained in the programming unit U mounted at the rear of the instrument. Three of the microswitches ($1, S~ and S3 in Figs. 2 and 3) are actuated by extensions on the gripper tube, the other three ($4, S5 and Ss) are actuated by three switching wheels driven by Mn. Fig. 3 gives the circuit of the programming unit. If it is desired to use less than 50 tubes, a pointer P (Fig. 2) may be put to the position of the last tube to be counted. At that position a microswitch (ST in Figs. 2 and 3) is closed and the programme is modified. Motor M~ then turns the disk to its starting position forgetting the empty positions; Mix and M remain inactive. Once the starting position is reached the normal programme is resumed because Ss opens. The changer may also be made to stop at the position indicated by the pointer, this is achieved by putting St0 (Fig. 3) of the programming unit in the position "stop". Some further details of the operation have been explained in the subscript of Fig. 2. The polythene tubes, moulded according to our
FIo. 1. Liquid sample changer. M i - - m o t o r for vertical m o v e m e n t of test-tubes; M i i - - m o t o r for rotation of disk a n d horizontal movem e n t of test-tubes; P - - p o i n t e r indicating last tube to be counted.
[See p. 139
(a)
(b)
FIo. 2. (a) Photograph of writing in methylene blue ink (two central figures of each line) and in "Ts" brand methylene blue ink (first and last figure of each line). (b) Autoradiogram of the same specimen after treatment with potassium ferrocyanide solution labelled with C 14.
138
Technical notes formed by dissolving, respectively, zinc sulphate in an excess of potassium thiocyanate, thallous sulphate in potassium bromide and cadmium sulphate in sodium iodide. I n conformance with the Fajans-Paneth rule, the anions that give the least soluble compounds with the dyestuffs are the most strongly adsorbed and therefore yield the most distinct autoradiograms. This enables inks to be differentiated, and later additions to be detected. For example, writing in blue ink prepared from "Ts" brand methylene blue adsorbs ferrocyanide ions more strongly than writing in ink containing an ordinary methylene blue dyestuff. This is clearly seen in Fig. 2. The paper itself also adsorbs radioactive isotopes, especially if the latter are inthe form of cations. Third grade writing paper adsorbs the ions less strongly than top and second grade paper of the same kind. Sized paper with large amounts of filler adsorbs silver ions to such an extent that ink marks are with great difficulty distinguished from the general background of the autoradiogram. The marks made by graphite pencils, graphite copying pencils and coloured pencils also adsorb radioactive isotopes. In the case of pencil marks containing basic dyestuffs, adsorption is due to the latter, and age-dependence is not always observed. Acid dyes present in a pencil mark (e.g. eosin) adsorb almost exclusively only anions. Soft graphite pencil marks containing more graphite and lampblack, adsorb actions better than marks made by hard pencils. Printing ink also adsorbs silver and thallium ions. This radioisotopic method makes it possible in certain cases to prepare more distinct photographic copies of poorly legible documents, and to detect additions made in a different writing medium or at a different time. B. E. GORDON V. K. LISICHENKO
Reference 1. MEZGER 0 . , RALL H. and HE,~ss W. Angew. Chem. 44, 645 (1931).
An Automatic Changer for Liquid Samples IN radiochemical and radiomedical work the yactivity of liquid samples is usually determined with the aid of a well-type NaI-scintillation counter. If large numbers of samples must be dealt with, manual handling of test-tubes and lead shielding becomes tedious and time consuming. In order to
139
eliminate this labour automatic changers for well-type counters have been developed. ~lm In this note another instrument of this kind is briefly described, which can handle up to 50 samples. In radiochemical work the changer can simultaneously be used as a fraction collector, e.g. in combination with an ionexchange column. Fig. 1 shows a photograph of the instrument, Fig. 2 gives a schematic cross-section. Fifty polythene tubes can be placed in slots of a Perspex disk K. This disk ,turns through one position each time a tube is changed. After the disk has turned gripper G (Fig. 2) actuated by gripper magnet M picks up a tube. Then the carriage F together with tube T which contains the gripper mechanism moves to the right (in Fig. 2) so that the test-tube is brought outside the perimeter of the disk. When the carriage has reached its extreme position the test-tube is lowered into the well-counter by a motor Mx, which moves tube T vertically. Apart from the gripper and its magnet, T contains a lead-filled section L which just closes a hole in the lead shield of the well-counter, when T is all the way down. Counting is started automatically as soon as the test-tube has reached its bottom position. After a predetermined count (or time) the scaler stops and prints elapsed time (or number of counts). Simultaneously the changer is started; the test-tube is taken up and replaced in its slot in the Perspex disk. The disk then turns to the next position and so on. The horizontal movement of the carriage F and the turning of the disk are accomplished by a motor Mm The sequence of the actions is determined by 6 microswitches S1-Ss that switch the motors and the gripper magnet through a system of relays contained in the programming unit U mounted at the rear of the instrument. Three of the microswitches ($1, S~ and S3 in Figs. 2 and 3) are actuated by extensions on the gripper tube, the other three ($4, S5 and Ss) are actuated by three switching wheels driven by Mn. Fig. 3 gives the circuit of the programming unit. If it is desired to use less than 50 tubes, a pointer P (Fig. 2) may be put to the position of the last tube to be counted. At that position a microswitch (ST in Figs. 2 and 3) is closed and the programme is modified. Motor M~ then turns the disk to its starting position forgetting the empty positions; Mix and M remain inactive. Once the starting position is reached the normal programme is resumed because Ss opens. The changer may also be made to stop at the position indicated by the pointer, this is achieved by putting St0 (Fig. 3) of the programming unit in the position "stop". Some further details of the operation have been explained in the subscript of Fig. 2. The polythene tubes, moulded according to our
FIo. 1. Liquid sample changer. M i - - m o t o r for vertical m o v e m e n t of test-tubes; M i i - - m o t o r for rotation of disk a n d horizontal movem e n t of test-tubes; P - - p o i n t e r indicating last tube to be counted.
[See p. 139