A Safe Way of Performing Some Dangerous Experiments. II. Construction of a Safety Dropper

Due to the high safety risks, chemistry instructors avoid demonstrating many remarkable experiments based on the addition of a liquid to a solid. Well-known examples of such demonstrations are various pyrotechnic mixtures of potassium chlorate and sugar (sucrose), which are usually activated with a drop of concentrated sulfuric acid. Other attractive demonstrations are the addition of water to freshly prepared magnesium phosphide and addition of water to burning magnesium. In all of these demonstrations the reaction that takes place immediately is very vigorous and can be hazardous for the instructor. Because chemistry teachers and instructors usually try to avoid performing experiments that include a hazard, a number of highly attractive experiments may remain unknown to the public. Using a simple homemade device called a safety dropper, one can perform all of these experiments with complete safety, both for the audience and the demonstrator. Details for performing some of these experiments as well as for the construction of the safety dropper are given in this paper. Video clips of demonstrations are included as an aid for inexperienced instructors.     

A Simple Home-built Gas Liquefaction Cell

Liquefaction of gases offers deeper insight into the properties of various substances that are gaseous under normal conditions; however, the boiling temperatures of a number of gases are very low, preventing their liquefaction by means of standard laboratory techniques. A simple gas-liquefaction cell (designed by the authors) that can operate down to liquid-nitrogen temperature (77 K) is described in this paper. The properties of several liquefied (condensed) gases (e.g., ammonia, chlorine, nitric oxide, oxygen, and ozonized oxygen) are studied using this cell. The cell is also suitable for demonstration experiments.     

A simple chemical method for visualization of sebaceous fingerprints on unfired cartridge cases by Prussian blue deposition

Russian Journal of Applied Chemistry - This paper presents a new method for chemical development of latent fingerprints on unfired cartridge cases and some metal surfaces. It is based on chemical...     

An Alternative Demonstration of Chemical Waves: A Video Clip of a One-Dimensional Wave in the Iodate–Arsenite System

A chemical wave was initiated in a system (glass tube or graduated cylinder) containing a water solution of potassium iodate, potassium hydrogen sulfate, starch, and an excess of potassium arsenite. A large number of photos (329) were taken with a digital camera (one snapshot every 30 seconds). These photos were linked to give a unique video clip. This video clip may be used as a time-saving alternative to the classical demonstration. Similar clips may be made for other long-lasting processes.     

Cuprous sulfide deposition method for visualization of latent fingermarks on unfired cartridge cases

A new chemical method for visualization of latent fingermarks on unfired cartridge cases is reported in this research. The method is based on two-step immersion of the cartridge cases in aqueous solutions of sulfuric acid and acidified sodium thiosulfate at room temperature. The chemical reactions that are occurring on the cartridge case's surface are leading to deposition of material in the furrows between the papillary line ridges thus visualizing the latent fingermark. The qualitative chemical composition of the as-deposited material was studied using X-ray powder diffraction analysis thus revealing that it corresponds to a low-crystalline hexagonal chalcocite phase cuprous sulfide (Cu₂S). The performance of the method was studied on fresh and aged fingermarks, and according to the results, it can visualize latent fingermarks that are up to 9 months old. The newly proposed method provides good performance considering the most important qualitative and quantitative parameters that describe each fingermark, that is, satisfactory contrast between the papillary line ridges and the background furrows, possibility of recognizing the pattern of each fingermark (arch, loop, and whorl), clarity and continuity of the friction ridges, and clarity of the second level characteristics and features. The proposed method is simple, fast, inexpensive, and reliable.     

Reactions of (benzamidomethyl)triethylammonium chloride with some inorganic nucleophiles in aqueous media

A variety of benzamidomethyl derivatives were prepared in water under alkaline conditions (pH>9) via reaction of (benzamidomethyl)triethylammonium chloride (1) with different inorganic nucleophiles. Reaction of 1 with hydroxylamine did not give the expected mono(benzamidomethyl)-hydroxylamine (3) but rather gave N,N- di(benzamidomethyl)hydroxylamine (2). Reactions of 1 with sodium azide and potassium cyanide gave benzamidomethyl azide (4a) and benzamidomethyl cyanide (4b) respectively. Potassium thiocyanate and sodium iodide reacted with 1, and the anion- exchanged products (benzamidomethyl)triethylammonium isothiocyanate (5a) and (benzamidomethyl)triethylammonium iodide (5b) were thus obtained. Cyanamide and potassium cyanate reacted readily with 1 and both gave the same mixture of di(benzamidomethyl)amine (7) and tri(benzamidomethyl)amine (8). All the reactions occurred smoothly, under mild conditions, to give the products in moderate to high yields.     

Spontaneous “Distillation.” Approaching Thermodynamic Equilibrium, A Marathon Experiment in Physical Chemistry

If the left side of a sealed tube (shaped like an inverted U) is filled with chloroform, after many months, the chloroform passes spontaneously to the right side of the vessel in accord with the minimum energy principle. A similar experiment with a half-filled disposable lighter can be performed successfully in a much shorter period (6–8 days). The rate of the process (spontaneous transfer of a substance from one side of the vessel to the other side) decays with time. Curve fitting reveals the existence of two independent exponential-decay processes. An explanation of the possible mechanisms for the transfer of the substance is offered in this paper.     

Volume Nonadditivity of Liquid Mixtures: Modifications to Classical Demonstrations

Departures from Raoults law are often found in liquid mixtures resulting in volume nonadditivity. Modifications are proposed for experiments demonstrating volume contraction of water/ethanol and volume expansion of ethyl acetate/carbon disulfide liquid mixtures. A layer of paraffin oil or water is used to prevent mixing of the liquids at an earlier stage then desired. A demonstration of volume expansion in a CS₂/ethyl acetate system is proposed as well. The modifications significantly improve the ease of the demonstrations, which can be made even more impressive by coloring the liquids. A reaction vessel of simple construction is offered for a more vivid demonstration of the phenomenon.     

Characterization and thermal decomposition of Mg<Subscript>2</Subscript>KH(AsO<Subscript>4</Subscript>)<Subscript>2</Subscript>·15H<Subscript>2</Subscript>O

In this work, we present first data on the infrared and Raman spectroscopic characteristics, thermal analysis and solid-state transformations of Mg₂KH(AsO₄)₂·15H₂O, which is a unique example of an acid salt containing dimeric units [H(AsO₄)₂] in its crystal structure. The infrared and Raman spectra recorded at ambient conditions have been studied, and an assignment of the observed vibrational bands has been proposed considering the crystal structure data. The thermal behavior of Mg₂KH(AsO₄)₂·15H₂O has been investigated by simultaneous TG/DTA/mass spectrometry experiments in the temperature range up to 1000 °C at different heating rates, and new data on the thermal stability and thermal dehydration of Mg₂KH(AsO₄)₂·15H₂O have been obtained. The phase composition after the dehydration processes in the temperature interval of 300–650 °C has been studied by combination of powder XRD and IR spectroscopic analyses. The spectroscopic and thermal properties of Mg₂KH(AsO₄)₂·15H₂O have been compared to those of the isostructural phosphate salt Mg₂KH(PO₄)₂·15H₂O.     

A Safe Way of Performing Some Dangerous Experiments. I. Construction of a Safety Spoon

The demonstrations of many remarkable experiments include a high safety risk (e.g. the reaction of large pieces of sodium/potassium with water; the reaction of potassium with liquid bromine; the reaction of sodium with concentrated sulfuric acid, etc.). Chemistry teachers and instructors are usually reluctant to perform experiments that include a hazard. As a result, a number of fascinating experiments remain unknown to the public. Using homemade devices (in this case a safety spoon) one can perform all the above experiments with complete safety, both for the audience and the demonstrator. Details for performing some of these dangerous experiments are given in this paper. In addition, the construction of a simple remote-controlled (RC) safety spoon is explained in detail. Video clips of two demonstrations are offered as an aid for inexperienced instructors.