MANUFACTURE OF COAL-GAS. 25 



The elements of water, O and H, are united in the ratio of 1 of the former 



to 2 of the latter, if we estimate them by bulk, or of 8 of the former and 1 of 







the latter, if by weight, oxygen being 16 times heavier than hydrogen. 



3. Bodies may unite in several proportions, but for each variation a distinct 

 compound is produced, which frequently bears no resemblance to the others. 

 Thus O H 2 (one volume of oxygen to two of hydrogen) forms water, as we 

 have already stated ; but O H, equal volumes of the same elements, produce 

 a liquid possessing very different properties, being highly corrosive, blistering 

 the skin when applied to it, and exploding violently by mere contact of certain 

 substances. 



4. Bodies unite with each other in a very simple ratio ; thus in gases, which 

 we can estimate by volume, we find that one volume of one substance unites 

 with one, two, or three of another, or in the proportions of 2 to 3, etc. ; as 

 O H 2 , O H, compounds of oxygen and hydrogen, or oxides of hydrogen as 

 they are called ; O C 2 , O C, O 3 C 2 , compounds of oxygen and carbon. By 

 weight the ratio appears less simple, if we compare different substances, 

 O 8 to H 1 , O 8 to C 6 ; but if we compare different compounds of the same 

 elements the proportions are still strikingly simple, as O s H 1 , O 16 H 1 , where 

 the proportions of O in the first to that in the second is as 1 to 2, the quantity 

 of hydrogen being the same. 



These facts are graphically presented to the mind by the hypothesis pro- 

 pounded by Dr. Dalton, of Manchester, under the name of the Atomic Theory. 

 He considers bodies to be formed of certain ultimate particles, or atoms. 

 When one body, A, unites with another, B, each atom contained in A seizes 

 upon one of those of B ; or one of A may unite with two or three of B, or two 

 with three, etc. These atoms are united by affinity, and the compound mole- 

 cule or assemblage of atoms (A B, or A B B, or A A B B B) thus produced, be- 

 comes possessed of new properties, often bearing no resemblance to those of 

 its constituents. Admitting the size and weight of the atoms of bodies to be 

 constant, we see why the proportions in which they unite are likewise con- 

 stant. And supposing all these atoms to be of the same size, but of different 

 weights, we can account for the simple ratio in which they unite by bulk and 

 weight ; thus, if an atom of oxygen be sixteen times heavier than one of hy- 

 drogen, we shall have in the two compounds of these elements the proportions : 

 By volume. By weight. 



O H 2 , O H. O 16 H 2 , or O 16 H 1 . 



E 



