Hydrogen tubes

To a reaction flask were added 50 mL cotton seed oil and 2.5 g silica black-supported nickel catalyst, and the mixture was agitated until complete suspension was attained. Then the mixture was stirred with a mechanical stirrer for 10 min, and the flask was placed in a furnace and connected with a hydrogen tube that reached to the bottom of the flask. The flask was maintained at 180°C for different time intervals, while hydrogen was bubbled through at the rate of 400-450 bubbles/min at ordinary atmospheric pressure. At the end of hydrogenation period, the experiment was stopped, and the product was filtered through asbestos at 140°C. The degree of unsaturation for the oil was verified by iodine numbers. 

Quartz Tube Method the sample is burned in a quartz tube and a stream of purified air carries the combustion gases into a hydrogen peroxide solution. 

Arsenic present only in traces (in any form) can be detected by reducing it to arsine and then applying tests for the latter. In Marsh s test, dilute sulphuric acid is added dropwise through a thistle funnel to some arsenic-free zinc in a flask hydrogen is evolved and led out of the flask by a horizontal delivery tube. The arsenic-containing compound is then added to the zinc-acid solution, and the delivery tube heated in the middle. If arsenic is present, it is reduced to arsine by the zinc-acid reaction, for example ... 

The evolved arsine is decomposed to arsenic and hydrogen at the heated zone of the delivery tube hence arsenic deposits as a shiny black mirror beyond the heated zone. 

Lead formate separates from aqueous solution without water of crystallisation. It can therefore be used for the preparation of anhydrous formic acid. For this purpose, the powdered lead formate is placed in the inner tube of an ordinary jacketed cond ser, and there held loosely in position by plugs of glass-wool. The condenser is then clamped in an oblique position and the lower end fitted into a receiver closed with a calcium chloride tube. A current of dry hydrogen sulphide is passed down the inner tube of the condenser, whilst steam is passed through the jacket. The formic acid which is liberated... 

Place a few drops of nitromethane in a test tube, add about 3 times as much concentrated hydrochloric acid, and then a piece of granulated tin. The tin dissolves in the acid and the nascent hydrogen produced reduces the nitromethane to monomethylamine ... 

Place 0 5 ml. of the pyridine in a 200 ml. round- or flat-bottomed flask and add 34 ml. (30 g.) of benzene. Fit the flask with a reflux water-condenser, and then place it in a cold water-bath. If the experiment is conducted in a fume-cupboard, the top of the condenser can be closed with a calcium chloride tube bent downwards (as in Fig. 61, p. 105 or in Fig. 23(A), p. 45, where the outlet-tube A will carry the calcium chloride tube) and the hydrogen bromide subsequently allowed to escape if, however, the experiment is performed in the open laboratory, fit to the top of the condenser (or to the outlet-tube A) a glass delivery-tube which leads through a piece of rubber tubing to an inverted glass funnel, the rim of which dips just below the surface of some water... 

Dissolve 5 g. (5 ml.) of aniline in 50 ml. of warm dilute sulphuric acid in a conical flask and add 50 ml. of water. Place a thermometer in the solution, immerse the flask in a mixture of ice and water, and cool until the temperature of the stirred solution falls to 5°. Dissolve 4-5 g. of powdered sodium nitrite in 20 ml. of water, and add this solution in small quantities (about 2-3 ml. at a time) to the cold aniline sulphate solution. Keep tne latter well shaken and maintain the temperature at about 5° (see p. 183). When all the sodium nitrite solution has been added, transfer about 5 ml. of the cold solution to a test-tube for each of the following reactions. The remainder of the diazonium hydrogen sulphate solution must be kept in ice-water until required, and then when all the reactions have been carried out, the solution should be poured down the sink. 

Assemble an apparatus similar to that used in the prenous experiment, i.e., a 500 ml. conical flask fitted at the neck with a freshly-charged calcium chloride tube, a dropping-funnel, and in addition an outlet-tube joined to the water-pump so that dry air can be drawn through the calcium chloride tube and thence through the conical flask. The purpose of the air-stream is to remove as much as possible of the excess of hydrogen chloride. 

I. Carbon and Hydrogen. The presence of these elements is usually assumed. If a direct test is required, a mixture of about 01 g. of the powdered substance and 2-3 g. of finely powdered copper oxide is heated in the tube A (Fig. 68) and the... 

A mist of condensed water on the upper portion of the tube A indicates the presence of hydrogen. To detect the presence of hydrogen in this way, however, the copper oxide must first be strongly heated in a crucible and then allowed to cool in a good desiccator otherwise the water normally absorbed by the very hygroscopic copper oxide will always give a mist on the tube A. 

Now heat the tube very gently at first and then more strongly. A non-conden-sible product such as hydrogen or methane is best detected by collecting a sample of the gas in a test-tube as shown in Fig. 71(A). A condensible product such as benzene or phenol should be collected by twisting the delivery-tube downwards and collecting the liquid in a few ml. of water in a test-tube as shown In Fig. 71(B). 

There is no satisfactory chemical way of distinguishing betn een ethane and methane, both of which burn with an almost non-luminous flame this fact however is quite unimportant at this stage of the investigation. Hydrogen also burns with a non-luminous flame and w hen the open end of a test-tube full of the gas is placed in a Bunsen flame, a mild explosion with a very characteristic report takes place. 

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