98 CAVENDISH. 



ment. He placed water in a retort exposed to heat ; 

 the vapour of the retort, when the water boiled, was 

 passed through a tube (a gun barrel with the breech- 

 pin knocked out was generally used); the tube, if 

 made of earthenware, had iron filings placed in its 

 course ; it was placed in a fire ; its further extremity 

 was connected with a receiver, in which cold water or 

 mercury rose to fill it entirely. As the water slowly 

 boiled there came through the tube, and into the glass 

 receiver, a current of gas, which, upon examination, 

 was found to be hydrogen gas r while the iron filings 

 were converted into calx or oxide. The weight of the 

 gas produced, added to the weight acquired by the 

 gun barrel or by the filings during the process, was 

 found to be nearly equal to the weight lost by the 

 water in the retort. Hence the inference was, that 

 the lost portion of water had been decomposed into 

 its two elements, the oxygen gas forming the calx of 

 the iron and the hydrogen gas being received in the 



flass vessel. But the adversaries of the new doctrine 

 ad an answer to this inference far more formidable 

 than any that they could urge against the conclusion 

 drawn from the synthetical experiment. The analyti- 

 cal experiment was liable to all the uncertainty of the 

 process called the destructive distillation. The sub- 

 stances found might have been the product, and not 

 merely the educt of the process. It is known that if 

 coal or oleaginous bodies be distilled in close vessels 

 there are obtained gases and water and acids which 

 never existed in the matters subjected to the action of 

 the fire. The component parts of these matters enter 

 into new combinations with one another under the 

 action of heat, just as a tallow candle or an oil lamp 

 gives lamp-black and water in burning, though no 

 water, but only hydrogen, nor of course any lamp- 

 black, exists in the tallow and the oil. So, in Lavoi- 

 sier's experiment, the water might contain only oxygen 

 and hydrogen, and the action of the hot iron might 



