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ting coal-gas should be suitable for acetylene; since the former contains two of the impurities--sulphuretted hydrogen and ammonia--characteristic of crude acetylene. After removing the ammonia by washing with water, therefore, it was proposed to extract the sulphur by passing the acetylene through that variety of ferric hydroxide (hydrated oxide of iron) which is so serviceable in the case of coal-gas. The idea, however, was quite unsound: first, because it altogether ignores the phosphorus, which is the most objectionable impurity in acetylene, but is not present in coal- gas; secondly, because ferric hydroxide is used on gasworks to extract in a marketable form the sulphur which occurs as sulphuretted hydrogen, and true sulphuretted hydrogen need not exist in well-generated and well- washed acetylene to any appreciable extent; thirdly, because ferric hydroxide is not employed by gasmakers to remove sulphur compounds (this is done with lime), being quite incapable of extracting them, or the analogous sulphur compounds of crude acetylene.
About the same time three other processes based on somewhat better chemical knowledge were put forward. Pictet proposed leading the gas through a strong solution of calcium chloride and then through strong sulphuric acid, both maintained at a temperature of -20° to -40° C., finally washing the gas in a solution of some lead salt. Proof that such treatment would remove phosphorus to a sufficient degree is not altogether satisfactory; but apart from this the necessity of maintaining such low temperatures, far below that of the coldest winter's night, renders the idea wholly inadmissible for all domestic installations. Willgerodt suggested removing sulphuretted hydrogen by means of potassium hydroxide (caustic potash), then absorbing the phosphine in bromine water. For many reasons this process is only practicable in the laboratory. Bergé and Reychler proposed extracting both sulphuretted hydrogen and phosphine in an acid solution of mercuric chloride (corros