I shall finish this chapter by an experiment much less demonstrative than those already related, but which has appeared to make more impression than any other upon the minds of many people. When 16 ounces of alkohol are burnt in an apparatus[21] properly adapted for collecting all the water disengaged during the combustion, we obtain from 17 to 18 ounces of water. As no substance can furnish a product larger than its original bulk, it follows, that something else has united with the alkohol during its combustion; and I have already shown that this must be oxygen, or the base of air. Thus alkohol contains hydrogen, which is one of the elements of water; and the atmospheric air contains oxygen, which is the other element necessary to the composition of water. This experiment is a new proof that water is a compound substance. FOOTNOTES: [16] In the latter part of this work will be found a particular account of the processes necessary for separating the different kinds of gasses, and for determining their quantities.--A. [17] This expression Hydrogen has been very severely criticised by some, who pretend that it signifies engendered by water, and not that which engenders water. The experiments related in this chapter prove, that, when water is decomposed, hydrogen is produced, and that, when hydrogen is combined with oxygen, water is produced: So that we may say, with equal truth, that water is produced from hydrogen, or hydrogen is produced from water.--A. [18] See the nature of these salts in the second part of this book.--A. [19] By potash is here meant, pure or caustic alkali, deprived of carbonic acid by means of quick-lime: In general, we may observe here, that all the alkalies and earths must invariably be considered as in their pure or caustic state, unless otherwise expressed.--E. The method of obtaining this pure alkali of potash will be given in the sequel.--A. [20] See the third part of this work.--A. [21] See an account of this apparatus in the third part of this work.--A. CHAP. IX. _Of the quantities of Caloric disengaged from different species of Combustion._ We have already mentioned, that, when any body is burnt in the center of a hollow sphere of ice and supplied with air at the temperature of zero (32 deg.), the quantity of ice melted from the inside of the sphere becomes a measure of the relative quantities of caloric disengaged. Mr de la Place and I gave a description of the apparatus employed for this kind of experiment in the Memoirs of the Academy for 1780, p. 355; and a description and plate of the same apparatus will be found in the third part of this work. With this apparatus, phosphorus, charcoal, and hydrogen gas, gave the following results: One pound of phosphorus melted 100 libs. of ice. One pound of charcoal melted 96 libs. 8 oz. One pound of hydrogen gas melted 295 libs. 9 oz. 3-1/2 gros.