Hydrogen inflammation limit

Production of an explosive gas (hydrogen lower inflammable limit is 4% in air) ... 

Sulphide of liyclrogon is highly inflammable if burned in a limited quantity of air, the hydrogen is consumed, whilst most of the sulphur is deposited. By means of chlorine or nitric acid, it may he completely decomposed hence, chlorine acts as a disinfectant and purifier of sewers or rooms impregnated. with the odor of sulphide of hydrogen. The annexed represents the decomposition... 

Amongst the earliest experiments carried out with a view to the quantitative determination of the limits of inflammability of combustible gases were those of Davy with fire damp, wfliich is mainly methane, CH4. Owing to the importance of this gas m connection with gob fires and explosions in coal mines, several other workers have also investigated it. The value of the results, however, is restricted by the fact that firedamp, like most natural products, is subject to very considerable variation in composition.3 Even Davy recognised that it was not pure methane indeed, perfectly pure methane is not easy to prepare in quantity. The gas, as obtained from sodium acetate, may contain as much as 8 per cent, of hydrogen, as well as ethylene.4 No doubt this variation m composition is one contributory cause of the very varied results listed in the table on p. 93. 

Widely differing results have been obtained for the limits of inflammability of hydrogen-air mixtures, as is evident fiom the following table ... 

The following results have been obtained by different investigators (see p. 100) for the lower and upper limits of inflammability of mixtures of carbon monoxide and air. The wide divergence which characterises the published data for hydrogen is not so evident, for the results agree much more closely. Undoubtedly the most reliable are those of Coward and his co-workers. 

At the end of the eighteenth and the beginning of the nineteenth century the influence of metals and oxides on the decomposition of several substances was studied by many scientists. It was noticed that contact with different substances gives very different products. An example is the decomposition of alcohol in the presence of copper or iron, carbon and an inflammable gas is produced. In the presence of pumice stone decomposition into ethene and water was observed. In other words, selectivity was demonstrated. Many other important milestones can be mentioned we limit ourselves to a few. Thenard investigated the dissociation of ammonia in contact with metals. In 1813 he found that the dissociation occurs over various metals, provided they are hot. Later he systematically studied the dissociation of hydrogen peroxide. He concluded that some of the solids studied... 

The peroxisome catalase system catalyses the hydrogen peroxide (H2O2 (-dependent oxidation of ethanol to acetaldehyde and water. Normally it contributes little to the oxidation of alcohol because of the limited availability of hydrogen peroxide. However, activation of peroxisomal catalase, by the increased generation of hydrogen peroxide via peroxisomal /3-oxidation, leads to an increased metabolism of alcohol. This state may contribute to an alcohol-related inflammation and necrosis in alcoholic liver disease. 

Broader decomposition voltage window (up to > 4 V) and therefore deposition of metals which is impossible in aqueous solution No reaction with substrate No hydrogen evolution Large number of complex ions possible Poisonous effect Easy inflammability. Low conductivity. Relatively high cost Limited solubility of many salts Disintegration of change at the electrodes Moisture and oxygen sensitivity... 

Helium is used for air-ships, blimps, etc, its non-inflammability rendering it particularly suitable for these purposes although its lifting power is only hair that of pure hydrogen. To a limited extent helium is employed in thermometry and in lamps for yielding the A line in optical work. When inhaled with oxygen, helium is used as a cure for asthma and other ailments, such as croup and diphtheria, in which the windpipe is obstructed. 

A mixture of phosphine and oxygen may be stored in a glass tube at the ordinary temperature and at a pressure of about 1 mm. for many hours mthout appreciable combination. Yet a quite small increase of pressure will cause the mixture to burst into vivid flame. No premonitory increase in reaction rate is detectable at pressures just below the inflammation point. In a somewhat analogous way, if to a 300 c.c. quartz vessel at 650° C. we add 200 mm. hydrogen followed by 100 mm. oxygen, the rate of combination observable is normally quite slow. It becomes slower stfll if the pressure is reduced and at about 100 mm. is almost imperceptible. Yet, if the pressure is reduced by another mUlimetre or so below this limit, the mixture explodes with a bright flash and a sharp sound. 

When considering the combustion of hydrogen or some hydrocarbons, however, if we plot a curve of the limit of inflammation of the mixture in a pressure-temperature space, we obtain curve DCBA as shown in Figure 15.2. This curve divides the plane into two regions one on the right in which any mixture ignites spontaneously and a second region to the left of the curve in which the oxidation reaction occurs without inflammation. 

---