When suitable precautions are not taken to remove the heat liberated in an acetylene apparatus, the temperature of the calcium carbide occasionally rises to a remarkable degree. Investigating this point, Caro has studied the phenomena of heat production in a "dipping" generator-- _i.e._, an apparatus in which a cage of carbide is alternately immersed in and lifted out of a vessel containing water. Using a generator designed to supply five burners, he has found a maximum recording thermometer placed in the gas space of the apparatus to give readings generally between 60° and 100° C.; but in two tests out of ten he obtained temperatures of about 160° C. To determine the actual temperature of the calcium carbide itself, he scattered amongst the carbide charge fragments of different fusible metallic alloys which were known to melt or soften at certain different temperatures. In all his ten tests the alloys melting at 120° C. were fused completely; in two tests other alloys melting at 216° and 240° C. showed signs of fusion; and in one test an alloy melting at 280° C. began to soften. Working with an experimental apparatus constructed on the "dripping" principle-- _i.e._, a generator in which water is allowed to fall in single drops or as a fine stream upon a mass of carbide--with the deliberate object of ascertaining the highest temperatures capable of production when calcium carbide is decomposed in this particular fashion, and employing for the measurement of the heat a Le Chatelier thermo-couple, with its sensitive wires lying among the carbide lumps, Lewes has observed a maximum temperature of 674° C. to be reached in 19 minutes when water was dripped upon 227 grammes of carbide at a speed of about 8 grammes per minute. In other experiments he used a laboratory apparatus designed upon the "dipping" principle, and found maximum temperatures, in four different trials, of 703°, 734°, 754°, and 807° C., which were reached in periods of time ranging from 12 to 17 minutes. Even allowing for the greater delicacy of the instrument adopted by Lewes for measuring the temperature in comparison with the device employed by Caro, there still remains an astonishing difference between Caro's maximum of 280° and Lewes' maximum of 807° C. The explanation of this discrepancy is to be inferred from what has just been said. The generator used by Caro was properly made of metal, was quite small in size, was properly designed with some skill to prevent overheating as much as possible, and was worked at the speed for which it was intended--in a word, it was as good an apparatus as could be made of this particular type. Lewes' generator was simply a piece of glass and metal, in which provisions to avoid overheating were absent; and therefore the wide difference between the temperatures noted does not suggest any inaccuracy of observation or experiment, but shows what can be done to assist in the dissipation of heat by careful arrangement of parts.