Gases closed tube test

Action of an Acid on a Metal. Assemble the setup shown in Fig. 42. Put 8-10 pieces of granulated zinc in the test tube, pour in 5 ml of a 20% sulphuric acid solution and close the tube with a stopper provided with a gas-discharge tube with its end drawn out upward. Check the purity of the hydrogen evolving. 

Close the test tube under the water with your thumb, extract it from the bath, wrap it in a towel, bring it up to the flame of a burner and, after opening the test tube, light the gas mixture. What happens ... 

Pour about 350 ml of distilled water into a flask with a volume of 0.5-1 litre and saturate it with air by shaking it. Fill the flask of the apparatus and the gas-discharge tube with the water saturated with air. Close the flask, making sure that not a single air bubble remains in the flask and in the tube. Put a test tube filled with water onto the free end of the gas-discharge tube immersed in a bath with water and fasten it in a stand (the test tube and the stand are not shown in... 

Preparation. Put 1-2 g of iron sulphide into a test tube and pour in 5-8 ml of a 20% hydrochloric acid solution. Close the tube with a stopper provided with a drawn out gas-discharge tube (see Fig. 42). 

Preparation of Chromium(II) Chloride. (Perform one of the following two experiments.) 1. Put several pieces of metallic chromium into a test tube, pour in 2-3 ml of a 20% hydrochloric acid solution, and insert a stopper with a gas-discharge tube. Connect to the latter a rubber tube with a slot closed by a glass rod (a Bunsen valve. Fig. 125). What is the role of the slot in the rubber tube Identify the substance in the solution. Write the equation of the reaction. 

Preparation and Properties of Chromyl Chloride, a. Put a mixture of 1 g of sodium chloride with 1 g of potassium dichromate into a dry test tube, add a few drops of concentrated sulphuric acid, and close the tube with a stopper provided with a gas-discharge tube. Lower the other end of the latter into another dry test tube submerged in a beaker with cold water. Slightly heat the reaction mixture. What collects in the receiver Write the equations of the reactions. 

Preparation of Hydrofluoric Acid. Put 5 g of fluorite and 1 g of gypsum into a Teflon (polytetrafluoroethylene), lead, or copper test tube (why is gypsum added ). Pour 5 ml of a 96% sulphuric acid solution over the mixture, tightly close the test tube with a rubber stopper provided with a Teflon, lead, or copper gas-discharge tube. Lower the end of this tube into a Teflon, lead, copper, or paraffin-coated glass beaker containing 10 ml of water so that it only slightly touches the surface of the water (why ). Put an asbestos sheet between the beaker and the Teflon test tube. To speed up the reaction, it is recommended to immerse the Teflon test tube into a beaker with hot water. Why must the test tube not be heated directly by the flame of a burner ... 

The bomb is then placed in the jacket, and the gas inlet tube is fastened securely. The thermocouple is also inserted. From this point on, all operations should be performed on the other side of the wall separating the operator from the equipment. Hydrogen is bled into the bomb from the high-pressure tank, the valve to the tank is closed, and the bomb is allowed to stand for about a half hour in order to test for leaks. If a leak has developed, as indicated by a drop in pressure, one locates it by painting all the joints with a soap solution and looking for bubbles of gas, which indicate a leak. The connector is tightened, and if this does not stop the leak, the pressure in the system should be released, the connection disassembled, and the tapered end of the tube re-formed with a tool supplied for the purpose. These measures usually will stop the leak, but if they do not, it will be necessary to ream out the connector seat with the reamer designed for this purpose. 

A tube with obstacles can model some industrial explosions. A simple analysis indicates that there are two contributing factors involved in flame acceleration along a tube with obstacles. They are the character of the motion of the gas in front of the flame and the turbulence induced by the interaction of the motion of the gas in front of the flame with the boundary condition in the tube with obstacles. To study in detail the mechanism of flame acceleration by means of obstacles, explosion tests and measurements of the parameters of mean flow velocity and root mean squared (RMS) turbulent velocity were performed. The characteristics of methane-air and comstarch-air flame acceleration were investigated in a closed tube 0.19 m in diameter and 1,86 -m long filled with obstacles. The nonuniformity in the mean flow velocity and the RMS turbulent velocity across the tube with and without obstacles were measured in a substitutional tube in which the air free flow velocity ranged from 9 m/s to 177 m/s. Experimental results demonstrated that in the environment with obstacles flame acceleration caused by the nonuniformity of flow velocity is more efficient than that caused by the RMS turbulent velocity. 

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