OZOM- AND HYUKOGEN PEROXIDE DALTON'S LAW 213 



Besides this, hydrogen peroxide indicates another side of the subject 

 which is not less important, and is much clearer and more general. 



Hydrogen unites with oxygen in two degrees of oxidation : water 

 or hydrogen oxide, and oxygenated water or hydrogen peroxide ; for a 

 given quantity of hydrogen the peroxide contains twice as much oxygen 

 as does water. This is a fresh example confirming the correctness of 

 the law of multiple proportions, of which we have already made men- 

 tion in speaking of the water of crystallisation of salts. Now we can 

 formulate this law with entire clearness the law of multiple propor- 

 tions. If two radicles A, and B (either simple or compound substances), 

 unite together to form several compounds, A n B OT , A^B r . . . ., then 

 having expressed the compositions of all these compounds in such a ivay 

 that the quantity (by weight or volume) of one of the component parts 

 will be a constant quantity A, it will be observed that in all the compounds 

 AB (( , AB,, . ... the quantities of the other component part, B, will 

 always be in commensurable relation : generally in simple multiple 

 proportion that is, that a : b . . ., or m/nis to r/q as whole numbers, 

 for instance as 2 : 3 or 3 : 4. . . . 



The analysis of water shows that in 100 parts by weight it contains 

 11-112 parts by weight of hydrogen and 88*888 of oxygen, and the 

 analysis of peroxide of hydrogen shows that it contains 94-112 parts of 

 oxygen to 5 -888 parts of hydrogen. In this the analysis is expressed, 

 as analyses generally are, in percentages ; that is, it gives the amounts 

 of the elements in a hundred parts by weight of the substance. The 

 direct comparison of the percentage compositions of water and hydrogen 

 peroxide does not give any simple relation. But such a relation is 

 immediately observed if we calculate the composition of water and of 

 hydrogen peroxide, having taken either the quantity of oxygen or the 

 quantity of hydrogen as a constant quantity for instance, as unity. The 

 most simple proportions show that in water there are contained eight 

 parts of oxygen to one part of hydrogen, and in hydrogen peroxide 

 sixteen parts of oxygen to one part of hydrogen ; or one-eighth part of 

 hydrogen in water and one- sixteenth part of hydrogen in hydrogen 

 peroxide to one part of oxygen. Naturally, the analysis does not give 

 these figures with absolute exactness it gives them within a certain 

 degree of error but they approximate, as the error diminishes, to that 

 limit which is here given. The comparison of the quantities of hydrogen 

 and oxygen in the two substances above named, taking one of the com- 

 ponents as a constant quantity, gives an example of the application of 



as to foretell the degree of stability of different chemical states of equilibrium. The 

 commencement of elementary generalisations has been apprehended in only a few 



