Experiments with Liquid Nitrogen

Everything has its science with the exception of catching fleas That is an art. 

Oxygen was discovered three times first by Carl Scheele as fire air , 1774 by Joseph Priestley as dephlogisticated air and in the same year by Antoine Laurent Lavoisier as the air of life . 

Safety glasses must be worn Avoid skin contact with liquid nitrogen, as it can cause severe skin burns. 

Dewar vessels, hammer, wire, crucible tongs, rubber tubing, rubber ball, balloon, apple, pear, flower, safety glasses, leather gloves. 

A piece of rubber tubing is slowly dipped into liquid nitrogen. It loses its elasticity on cooling and shatters into many pieces on being hit with a hammer when cold. An apple or a rubber ball behave in a similar manner these can be dipped into the liquid nitrogen with the help of a wire loop. 

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Accdg to Marshall (Ref 2), expls at high temps are considerably more sensitive conversely their sensitiveness is reduced on cooling them. In experiments conducted in France by Kling Florentin (Ref 1), expls, as well as their, detonators were cooled to temp —80°C by means of solid carbon dioxide and acetone, or to about —190° with liquid nitrogen. Table E2 lists the results of the tests... 

Experimental method. In the flask P (see Fig. 1) a mixture was made up at an initial pressure of 200 mm and a temperature of 20° C. Then an electric heater was fitted on to the flask which was heated together with the explosive mixture in it. We estimated the temperature of the mixture by the change in pressure. After a steady temperature was reached (varying in different experiments between 200-300° C) the mixture was exploded. The heater was then removed and the nitric oxides determined as in 3. It was shown by special experiments that even after the flask had been in the heater for fifteen minutes there was no loss of nitric oxide after the explosion. In some experiments the mixture was cooled before the explosion, the flask P being wrapped in a cloth and abundantly wetted with liquid nitrogen. 

The initial pressure was 5 kg per cm2. The carbon monoxide was condensed in a trap cooled with liquid nitrogen, whence it was evaporated into a bomb at a pressure of 1-2 kg per cm2. Air was then admitted from a container bringing the pressure up to 5 kg per cm2. The explosion products were collected in a glass flask in which the nitric oxide content was determined as usual. Control experiments showed that a delay in transferring the explosion products to the flask reduced the yield of nitric oxide in a geometrical progression by 10% per minute. This was apparently due to corrosion and in succeeding experiments the time of transfer did not exceed one minute. 

The properties of the dual-film electrode were characterized by in situ Fourier transform infrared (FTIR) reflection absorption spectroscopy [3]. The FTIR spectrometer used was a Shimadzu FTIR-8100M equipped with a wide-band mercury cadmium teluride (MCT) detector cooled with liquid nitrogen. In situ FTIR measurements were carried out in a spectroelectro-chemical cell in which the dual-film electrode was pushed against an IR transparent silicon window to form a thin layer of solution. A total of 100 interferometric scans was accumulated with the electrode polarized at a given potential. The potential was then shifted to the cathodic side, and a new spectrum with the same number of scans was assembled. The reference electrode used in this experiment was an Ag I AgCl I saturated KCl electrode. The IR spectra are represented as AR/R in the normalized form, where AR=R-R(E ), and R and R(E ) are the reflected intensity measured at a desired potential and a base potential, respectively. 

Dynamic mechanical properties of all pure components and blends were measured as a function of percent strain and indicated a linear viscoelastic region up to approximately 30-35 percent. Therefore, all rheological experiments were conducted at a strain rate of 20 percent. In cases where thermal degradation occurred (as seen in time sweep), the heating chamber was continuously purged with liquid nitrogen. Frequency sweeps, and in some cases frequency-temperature sweeps, were performed on all pure components and blends. 

The almost complete conversion of CO to hydrocarbons, H20, and C02, obtained by cooling the bottom of the reactor, is reversible. Several additional experiments (at 12 torr), where the gases reacted for 3 minutes while the bottom of the reactor was cooled with liquid nitrogen, the reactor then warmed to room temperature in a few seconds with a water bath, and the gases reacted for 2 more minutes, gave essentially the same product compositions as for the runs shown in Figures 1 and 2. 

BET surface area measurements were carried out using Carlo Erba sorptometer with liquid nitrogen at 77K. The samples were degassed at 393K prior to all the experiments. The BET surface areas of the gel, commercial cuid the mixed oxide samples were found to be 100, 10 and 250mVg respectively. 

Conditions. NH3 gas is introduced into the source from a reservoir kept at —40°C. In most of these experiments the pressure in the ion source was 3 X 10 3 torr (1014 molecules/cc.). The pumping rate is 5 liters/sec. when the cold finger is filled with liquid nitrogen, the flowing rate being 6 X 1017 molecules/sec., and the transit time of molecules between the interaction zone and the cold finger — 2 X 10"s sec. 

The primary oxidation products were passed through several layers of platinized asbestos and platinum wire formed into a star pattern. A series of experiments on the combustion of diphenyl sulphoxide showed that at 850°C and in the presence of a platinum catalyst sulphur is quantitatively converted into sulphur dioxide with no sulphur trioxide being produced. The oxidation temperature can be increased to 1200°C if a vanadium catalyst is used. The water is absorbed in a tube containing calcium sulphate, which helps to prevent the formation of sulphurous acid. Carbon dioxide and sulphur dioxide were concentrated in a U-shaped trap cooled with liquid nitrogen, and were subsequently analysed by GC at 92°C using a 6-m column filled with dinonyl phthalate. The content of sulphur in the sample was derived from the sulphur dioxide peak area with due regard to the weight of the sample and the calibration coefficient. 

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