METHODS AND APPARATUS FOR VISUALISING A PRINT ON AN OBJECT
20200046266 ยท 2020-02-13
Assignee
Inventors
- ROBERTO STEFANO PASQUALE KING (LOUGHBOROUGH, GB)
- PAUL FRANCIS KELLY (LOUGHBOROUGH, GB)
- STEVEN GEOFFREY THORNGATE (SALISBURY, GB)
Cpc classification
International classification
Abstract
The present invention provides a method for the production of a metal halide adduct of S.sub.4N.sub.4, in particular a specific copper adduct of S.sub.4N.sub.4, for the visualisation of a print on an object, in particular a fingerprint on a metal object. The present invention also provides a method and apparatus for visualising a print on an object, using S.sub.2N.sub.2 obtained from a metal halide adduct of S.sub.4N.sub.4.
Claims
1. A method for the production of a metal halide adduct of S.sub.4N.sub.4 comprising the steps of. a. reacting S.sub.2Cl.sub.2 with gaseous ammonia in a dry solvent to produce crude S.sub.4N.sub.4; b. without purification, adding the crude S.sub.4N.sub.4 to a solution of metal halide in alcohol and stirring until no S.sub.4N.sub.4 remains; and c. obtaining the metal halide adduct of S.sub.4N.sub.4 by removal of the alcohol.
2. A method according to claim 1 wherein the metal halide is CuBr.sub.2 and the metal halide adduct of S.sub.4N.sub.4 is CuBr.S.sub.4N.sub.4.
3. A method according to claim 1 wherein the dry solvent is carbon tetrachloride or tetrachloroethylene.
4. A method according to claim 1 wherein the alcohol is methanol.
5. A method according to claim 1 wherein step (a) is conducted at a temperature of less than about 100 C.
6. A method according to claim 1, wherein step (b) is conducted at a temperature of from about 40 C. to about 60 C.
7. A method for visualising a print on an object comprising the steps of: a. placing within an apparatus: i. the object potentially comprising at least one print; and ii. the metal halide adduct of S.sub.4N.sub.4 produced by the method according to claim 1; b. heating the metal halide adduct of S.sub.4N.sub.4 under vacuum to produce S.sub.2N.sub.2 vapour; c. cooling the S.sub.2N.sub.2 vapour at or in proximity to the object to promote a phase change to solid S.sub.2N.sub.2: and d. heating the solid S.sub.2N.sub.2 back to S.sub.2N.sub.2 vapour to facilitate interaction of the S.sub.2N.sub.2 vapour with the object to visualise the print.
8. A method according to claim 7 wherein for step b) the metal halide adduct of S.sub.4N.sub.4 is heated to from about 160 C. to about 170 C.
9. A method according to claim 7 wherein for step c) the S.sub.2N.sub.2 vapour is cooled to a temperature of from about 25 C. to about 0 C.
10. A method according to claim 7 wherein for step d) the solid S.sub.2N.sub.2 is heated to generate S.sub.2N.sub.2 vapour at a temperature of from about 25 C. to about 50 C.
11. A method according claim 7 wherein the object is contacted with the S.sub.2N.sub.2 vapour for at least 1 to 15 minutes.
12. A method according to claim 7 wherein the vacuum is at a pressure of from about 1.3310.sup.6 Pa (110.sup.9 mm/Hg) to about 133 Pa (1 mmHg).
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. An apparatus comprising: a first chamber comprising a heating element for heating a metal halide adduct of S.sub.4N.sub.4 to produce S.sub.2N.sub.2 vapour, the metal halide adduct of S.sub.4N.sub.4 having been produced by (i) reacting S.sub.2Cl.sub.2 with gaseous ammonia in a dry solvent to produce crude S.sub.4N.sub.4, (ii) without purification, adding the crude S.sub.4N.sub.4 to a solution of metal halide in alcohol and stirring until no S.sub.4N.sub.4 remains, and (iii) obtaining the metal halide adduct of S.sub.4N.sub.4 by removal of the alcohol; a second chamber in communication with the first chamber and in which an object potentially comprising at least one print can be arranged, the second chamber comprising a cooling element for cooling S.sub.2N.sub.2 vapour produced from the first chamber; and a vacuum pump in communication with the second chamber; wherein in use the S.sub.2N.sub.2 vapour is cooled in the second chamber at or proximal to the object, to facilitate interaction between the S.sub.2N.sub.2 vapour and the object.
Description
[0089] The invention will now be described with reference to the following non-limiting examples and figures, in which:
[0090]
[0091]
[0092]
[0093] As shown in
[0094] In the apparatus (1) shown, the chamber is connected to a vacuum pump (not shown) via a tube (5).
[0095] CuBr.S.sub.4N.sub.4 (6) is placed in a side arm (7) connected to the chamber (3). The side arm (7) and the tube (5) are positioned such that when the CuBr.S.sub.4N.sub.4 (6) is heated via a heating element (8) to produce S.sub.2N.sub.2 vapour, the vapour enters the chamber (3) at a point such that the vapour subsequently cools to form solid S.sub.2N.sub.2 proximal to the cooling element (9) i.e. the S.sub.2N.sub.2 vapour is not immediately removed by the vacuum pump which is typically on whilst the CuBr.S.sub.4N.sub.4 (6) is heated. After cooling, the solid S.sub.2N.sub.2 is converted via heating to S.sub.2N.sub.2 vapour in order to contact the object (2) comprising a print. Upon completing the duration in which the S.sub.2N.sub.2 vapour contacts the object (2), the vapour is removed from the chamber (3) via the tube (5) connected to the vacuum pump.
[0096] When a vacuum is to be used in the present invention, the apparatus (1) must be capable of holding a vacuum. Vacuum taps (10a, 10b) are provided, which can be closed to maintain a static vacuum inside chamber (3). Thus, the interior of the chamber (3) can be maintained under vacuum even after the vacuum pump has been turned off. A suitable chamber (3) would be able to maintain a pressure of from about 1.3310.sup.6 Pa (110.sup.9 mm/Hg) to about 133 Pa (1 mmHg) without the assistance of a vacuum pump.
[0097] In use, object (2) to be treated for latent fingerprints is arranged inside chamber (3) with a small quantity (approx. 0.5-1 g) of precursor CuBr.S.sub.4N.sub.4 (6) in crystal form, placed in the side arm (7) connected to the chamber (3). The chamber (3) is then evacuated by a vacuum pump via tube (5), connected to the other side of the chamber, while a cooling element (9) associated with the base of chamber (3) is used to create a chilled area.
[0098] CuBr.S.sub.4N.sub.4 (6) in the side arm (7) is heated at a temperature of 160 C. under a vacuum of about 13 Pa (0.1 mmHg).
[0099] During the step of heating of CuBr.S.sub.4N.sub.4 (6), the adduct decomposes and releases S.sub.2N.sub.2 vapour. The atmosphere in the chamber (3) containing the object. (2) comprising a print is cooled using a cooling element (9) at the same time as the side arm (7) is heated, with the resultant effect that the S.sub.2N.sub.2 vapour is cooled upon entering the chamber (3).
[0100] After heating CuBr.S.sub.4N.sub.4 (6) for sufficient time to release enough S.sub.2N.sub.2 vapour for condensing on the cooling element (9), the vacuum taps (10a, 10b) are closed and a static vacuum is maintained.
[0101] The cooling effect provided by the cooling element (9) is then stopped, and the chamber (3) is then heated to about 30 C. for between 5 minutes and 2 hours, for example for about 15 minutes.
[0102] The chamber (6) containing the object (2) comprising a print to be visualised can be then left to develop for at least 15 minutes.
[0103] Fingerprint development is observed as S.sub.2N.sub.2 vapour polymerises on the object (2) being treated and when maximum contrast between ridges and background is obtained excess vapour is vented from the chamber (3) and the marks photographed.
[0104] Various modifications to the apparatus (1) can be made as will be apparent to those skilled in the art. For example, the metal halide adduct of S.sub.4N.sub.4 may be held in containment material in which containment material includes: a mesh; a stainless steel mesh; an ampule; a metal tray with a removable seal; a paper sachet; and/or a plastic container. Other means apparent to the skilled person could be envisaged for heating the metal halide adduct of S.sub.4N.sub.4, for example using heating tape around a containment material in which the metal halide adduct of S.sub.4N.sub.4 may be held, or alternative heating means surrounding the whole metal halide adduct of S.sub.4N.sub.4 to ensure that no cold spots develop which allows premature solidification of the S.sub.2N.sub.2 vapour. Furthermore, other means could be envisaged for cooling the chamber (3), for example an ice/water bath or cold-finger arrangement. The apparatus (1) may be a man-portable device. Furthermore, the apparatus (1) may be built at least predominantly of stainless steel. The size of the chamber (3) can be varied according to the desired application. For example, chamber (3) could provide for a relatively small enclosed volume to specifically deal with smaller items such as cartridge casings.
[0105] The present invention is illustrated by the following non-limiting Examples.
Example 1: Synthesis of Crude Tetrasulfur Tetranitride (S.SUB.4.N.SUB.4.)
[0106] Sulfur (I) dichloride, S.sub.2Cl.sub.2 (50.0 ml, 84.00 g, 0.62 moles) and dry carbon tetrachloride (1400 cm.sup.3) were placed into a two litre, three necked, round bottomed flask. A paddle stirrer was inserted through the main neck of the flask and open-end gas inlet tubes were inserted through the remaining necks. While the mixture was stirred briskly (ca. 500 rpm), a steady stream of chlorine gas was passed directly into the solution, until a distinct green layer of chlorine was clearly visible in the headspace. The flow of chlorine was then stopped and a flow of nitrogen was passed through the solution until the excess chlorine was removed. The round bottomed flask was then immersed into a water/ice bath, and ammonia gas was passed through the stirred solution, keeping the temperature below 50 C. Levels of carbon tetrachloride were maintained throughout the reaction. After approximately 3 hours, the reaction mixture was golden-poppy in colour and pH>8, at this point the reaction was ceased. The reaction mixture was carefully filtered, under vacuum, on a large Buchner funnel. The damp solid material collected was vigorously slurried with de-ionised water (1000 cm.sup.3) for 5-10 minutes and the remaining undissolved solid allowed to dry, in air, for 2 days. This crude form of the product was then used for the subsequent synthesis of the CuBr.S.sub.4N.sub.4 adduct. IR: 922, 688, 539 cm.sup.1.
Example 2: Synthesis of Crude Tetrasulfur Tetranitride (S.SUB.4.N.SUB.4.)
[0107] Sulfur (I) dichloride, S.sub.2Cl.sub.2 (85 cm.sup.3, 142.80 g, 1.054 moles) and tetrachloroethylene (2100 cm.sup.3) were placed into a three litre, three necked, round bottomed flask. A paddle stirrer was inserted through the main neck of the flask and open-end gas inlet tubes were inserted through the remaining necks. While the mixture was stirred briskly (ca. 500 rpm), a steady stream of chlorine gas was passed directly into the solution, until a distinct green layer of chlorine was clearly visible in the headspace. The flow of chlorine was then stopped and a flow of nitrogen was passed through the solution until the excess chlorine was removed. The round bottomed flask was then immersed into a water/ice bath, and ammonia gas was passed through the stirred solution, keeping the temperature below 50 C. Levels of tetrachloroethylene were maintained throughout the reaction. After approximately 3 hours, the reaction mixture was golden-poppy in colour and pH>8, at this point the reaction was ceased. The reaction mixture was carefully filtered, under vacuum, on a large Buchner funnel. The damp solid material collected was vigorously slurried with de-ionised water (2000 cm.sup.3) for 5-10 minutes, then washed with diethyl ether (ca. 50 cm.sup.3), and the remaining undissolved solid allowed to dry, in air, for 2 days. This crude form of the product (ca. 50 g) was then used for the subsequent synthesis of the CuBr.S.sub.4N.sub.4 adduct. IR: 922, 688, 539 cm.sup.1.
Example 3: Synthesis of CuBr.S.SUB.4.N.SUB.4
[0108] In a round-bottomed flask, CuBr.sub.2 (6.059 g, 0.027 moles) was dissolved in methanol (120 cm.sup.3) and non-purified S.sub.4N.sub.4 (5.002 g, approx 0.027 moles) obtained via the process of either Example 1 or 2 was added. The flask was sealed with a stopper and stirred at 50 C. for 45 minutes until no solid S.sub.4N.sub.4 remained. The resulting anthracite-black crystals of CuBr.S.sub.4N.sub.4 were collected via vacuum filtration and washed with methanol (350 cm.sup.3), and after drying stored in sample vials in air. Typical yield=6.410 g (72%). Anal. Calcd. for CuBr.S.sub.4N.sub.4: N=17.1%; Found: N=17.1%. IR: 910, 694, 535 cm.sup.1.
Example 4: S.SUB.2.N.SUB.2 .Synthesis and Sample Treatment
[0109] Samples were pre-loaded into the development (treatment) chamber using appropriate fixing methods (double-sided tape, Velcro, or clipped fastenings). The treatment chamber was sealed using the rubber O-ring gasket to join the two halves of the assembly. A B32 ground-glass head unit was then attached through the central opening of the treatment chamber, ensuring all joints and taps were well greased. The chamber was placed into a deep walled container/dish acting as a cooling bath and then evacuated at ca. 0.1 mm/Hg for approximately 1 hour.
[0110] The side-arm containing CuBr.S.sub.4N.sub.4 (0.6 g, 1.83 mmol) was then attached, again ensuring the B19 ground-glass joint was well greased, and the Isopad S45 heating tape, connected to an Isopad ML10 temperature controller, was placed around the majority of the side-arm (allowing only the bottom 1 inch to be uncovered). The Young's tap was then opened, allowing the side-arm to be evacuated for a further 30 mins. During this time, salt/ice was added to the container that the treatment chamber was rested in, so that the effective temperature was approximately 5 C. or below.
[0111] The heating tape was then switched on and allowed to establish a temperature of approximately 180 C. (ca. 5 min). When this point was reached, a pre-heated oil bath at 160 C. was raised to submerge the lower portion of the side-arm that was not directly heated by the heating tape.
[0112] The CuBr.S.sub.4N.sub.4 was heated in this fashion for approximately 50-60 mins, until its initial crystalline black appearance had changed to a dull grey/green colour. After this point, the Young's tap was closed along with the main vacuum tap (ensuring a static vacuum), the entire setup removed from the salt/ice bath and the base gently warmed to ca. 30 C. for 15 mins to allow the isolated S.sub.2N.sub.2 to enter the vapour state within the chamber.
[0113] Observation of samples within the chamber allowed appropriate development time to be recognised. Routinely, samples were not left exposed to S.sub.2N.sub.2 for longer than 24 hours. Removal of samples from the chamber was simply achieved by opening the vacuum tap to release the vacuum and careful dismantling of the two chamber halves to allow samples to be retrieved.
[0114] Typically, after the visualisation of the print, the object can be stored under normal atmospheric conditions. However, optimum conditions for storage would depend on the nature of the material that the object comprised.
[0115] If the object is metal then it is preferred that it is stored under conditions which prevent oxidation or corrosion effects, for example under dry, oxygen free conditions. The exact condition would depend on the reactivity of the metal with air and would be apparent to those skilled in the art.
[0116] Preferred storage conditions include an inert dry atmosphere, typically at room temperature or below, such from about 20 C. to about 20 C., for example from about 0 C. and 10 C., and that is optionally dark.
Example 5: Visualisation of a print on brass
[0117] A fingerprint was deposited on the a brass object and left for several hours before being washed off using water, then acetone, and finally buffed and dried to a polish with tissue paper. A photograph of the surface of the object on which the print had been applied after the washing and polishing steps viewed under an optical microscope at 10 magnification is shown in
[0118] The brass object was then subjected to a method as set out in Example 4.
[0119] Comparison of
[0120] It will be understood that the present invention has been described above purely by way of example, and modification of detail can be made within the scope of the invention. Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.
[0121] Moreover, the invention has been described with specific reference to fingerprint visualisation. It will be understood that this is not intended to be limiting and the invention may be used more generally. For example, the invention may be used more generally in the forensic fields, and may be used in other chemical applications. Additional applications of the invention will occur to the skilled person.