52 A CHEMICAL TRIAD. 



respectively. In like manner, each of the sixty and more kinds 

 of matter has its own combining, or equivalent, or atomic 

 number : for instance, the atomic number of the metal copper 

 is 32, and that of silver 110 ; by which we mean to say, that 

 if one part of hydrogen can do a certain amount of work, it 

 w T ill require eight parts of oxygen, thirty-six of chlorine, one 

 hundred and eight of silver, and thirty-two of copper, to do 

 the same amount of work. 



But of what are these numbers the respective weights 1 

 grains, ounces, pounds, or, in short, ivhal ? Just whatever you 

 please. Atoms being inconceivably small, we are unable to 

 weigh them absolutely : we can only ascertain the relation 

 subsisting between their weights ; the ratio according to which 

 is lighter or heavier than its neighbours. 



Cui bono ? What's the advantage ? It is universal. 

 Everything truthful and reliable in analytical and operative 

 chemistry depends upon an application of the facts above 

 mentioned. Take an example. If silver be thrown into aqua- 

 fortis, the metal dissolves and disappears, but it still exists in 

 the aquafortis. The piece of silver, we will assume, weighed 

 110 grains. A chemist wishes to get this silver, but the aqua- 

 fortis will not let him have it until it receives a quid pro quo. 

 The greedy solvent will be content with copper, and so the 

 chemist determines to give it copper ; but he wishes to give it 

 the exact quantity required, neither more nor less. Dalton's 

 law teaches the chemist that 32* grains of copper will be the 

 exact quantity. He adds that amount, and down goes the 

 silver. It was a great thing, even practically speaking, to 

 have made this discovery. 



Dalton furnishes a rare example of what a strong will and 

 ii vigorous intellect, when they co-exist, can do. He was the 

 son of a Cumberland weaver a very poor weaver, earning 



* In the language of present chemical nomenclature, copper is said to 

 be a di-valent, and its combining weight 63'5 say, in round numbers, 64 : 

 double the formerly received atomic weight as given above, Study the two 

 concluding paragraphs at p. 63. 



