200 Dr. Macneven's Exposition of [Sept. 



8 to 1. Now, if water be a combination of 1 atom of oxygen to 



1 atom of hydrogen, it follows that the atom of oxygen weighs 

 eight times as much as the atom of hydrogen. 



8. We may give to this reasoning a more general form by 

 putting ?/ for any volume of hydro2;en, and x for the same volume 

 of oxygen ; then there are in water, by experiment, 2 i/ + I x ; 

 and since 1 x weighs 16" y, the constituents of water may be 

 expressed in weights of ?/ ; thus, '2 y -\- 16 ?/ = 18 y, the whole 

 weight of water. Supposing this lUO, we have 18 y = 100 and 

 y = 100 -^ 18 =: 5*555, weight of 1 y, or one volume of hydro- 

 gen ; but there are 2 y, or two volumes ; consequently 5*555 x 



2 = 11*110 gives the weight of hydrogen in 100 of water. 



If we subtract the weight thus found from the compound, we 

 have 100 - 11*110 = 88*890, the weight of oxygen in 100 of 

 water. 



Now 88*890 : 11*110 :: 8 : 1 nearly. 



9. The weight of an atom of oxygen or hydrogen may also be 

 deduced from the specific gravity of those gases, and it is the 

 more usual way, for the weights of equal volumes are to each 

 other as the specific gravities. Thus the specific gravity of 

 hydrogen being 0*0694, and that of oxygen VI 1 1. If we take y 

 to represent the weight of any number of atoms of hydrogen in a 

 volume, we shall have this proportion 0*0694 : 1*111 :: 7/ : 1*111 



X y -T- 0*0694 = 16 ?/ ; and if 16 y equal the weight of the 

 atoms in a volume of oxygen, i/ x 2 = 2 j/ is the expression for 

 the weiglit of an equal number of the atoms of hydrogen ; but 

 2 y : \Qy :: 1 : 8. Therefore, the atom of hydrogen is but one- 

 eighth of the weight of an atom of oxygen. 



10. Another mode of obtainino; the relative weights of the 

 atoms from the specific gravity of their gases is to compare the 

 specific gravity of each gas with the specific gravity and weight 

 of the common standard atmospheric air ; and as they are to one 

 common third weight they will be to one another, thus: 



1*000 : 1*111 :: 30*5 : 33*888 weight of oxygen 

 1*000 : 0*0694 :: 30*5 : 2*117 weight of hydrogen 



The numbers 1*000 representthe specific gravity of atmospheric 

 air; 1*111 that of oxygen gas ; 30*5 the weight in grs. of 100 

 cubic inches atmospheric air ; and 33*888 the weight of the same 

 measure of oxygen gas. 



11. The same law is observed by other elementary bodies in a 

 gaseous state. They unite in such proportions that one volume 

 of the gas of one combines with an equal volume of the gas of 

 the other, or with two or v/ith three volumes, 8v.c. of that gas 

 without any intermediate fraction ; so that in these combinations 

 one at least of the elements ought always to be considered as 

 unity. According to the atomic theory, this means that an 

 atom of one of the elements combines with one or more entire 

 atoms of the other, for there can be no fraction of an atom.. 



