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han acetylene itself. Manifestly, therefore, the ideal diluent for acetylene is a substance which possesses as high a flame temperature as acetylene and a certain degree of intrinsic illuminating power, while the lower the flame temperature of the diluent and the less its intrinsic illuminating power, the less efficiently will the acetylene act as an enriching material. According to Love, Hempel, Wedding, and others, if acetylene is mixed with coal-gas in amounts up to 8 per cent. or thereabouts, the illuminating power of the mixture increases about 1 candle for every 1 per cent. of acetylene present: a fact which is usually expressed by saying that with coal-gas the enrichment value of acetylene is 1 candle per 1 per cent. Above 8 per cent., the enrichment value of acetylene rises, Love having found an increase in illuminating power, for each 1 per cent. of acetylene in the mixture, of 1.42 candles with 11.28 per cent. of acetylene; and of 1.54 candles with 17.62 per cent. of acetylene. Theoretically, if the illuminating power of acetylene is taken at 240 candles, its enrichment value should be (240 / 100 =) 2.4 candles per 1 per cent.; and since, in the case of coal-gas, its actual enrichment value falls seriously below this figure, it is clear that coal-gas is not an economical diluent for it. Moreover, coal-gas can be enriched by other methods much more cheaply than with acetylene. Simple ("blue") water-gas, according to Love, requires more than 10 per cent. of acetylene to be added to it before a luminous flame is produced; while a mixture of 20.3 per cent. of acetylene and 79.7 per cent. of water-gas had an illuminating power of 15.47 candles. Every addition to the proportion of acetylene when it amounted to 20 per cent. and upwards of the mixture had a very appreciable effect on the illuminating power of the latter. Thus with 27.84 per cent. of acetylene, the illuminating power of the mixture was 40.87 candles; with 38.00 per cent. of acetylene it was 73.96 candles. Acetylene would not be an economical age