1820.] the Atomic Theory. 197 



effects no change in the nature of this salt, but remains distin- 

 guishable itself as potash ; or if, instead of potash, there be 

 added an excess of acid, it does not alter the nature of the salt, 

 but is recognized, in like manner, by its own acid character. 

 The quantity of one substance entering into chemical union is 

 limited, therefore, by that of the other. To this phenomenon 

 the older chemists, expressing the fact only, gave the name of 

 saturation. And having further observed that an ounce of 

 different acids require unequal quantities of potash for saturation, 

 they established that the point of saturation varied with the 

 substance, and that it was different in different bodies. 



Modern chemists have given to this law the name of definite 

 proportion, meaning thereby to express a fact which they have 

 traced more extensively and correctly than their predecessors. 

 Indeed all chemical compounds contain the same proportion of 

 constituents with the most rigid accuracy, no variation ever 

 taking place in this respect. The whole science of chemistry is 

 founded on the permanency of chemical compounds, 



4. Richter, in his geometry of the chemical elements, gave 

 great extension to the doctrine of definite proportions, and 

 enriched it by a vast number of new and important observations. 

 He observed that when two neutral salts which mutually decom- 

 pose each other are mixed together, the two newly formed salts 

 still retain the same neutral state as the two original ones from 

 which they were formed. He drew up the results of many expe- 

 riments in tables exhibiting the weight of each base, capable of 

 saturating 100 parts by weight of each acid, and the weight of 

 each acid capable of saturating 100 parts by weight of each base. 

 He found that the different bases follow exactly the same order 

 in each of the tables, and, he observed further, that the numbers 

 in each table constitute a series which have the same ratio to 

 each other in all the tables. Suppose, for example, that in the 

 table representing the muriates, the quantity of potash requisite 

 to saturate 100 parts of muriatic acid were three times as great 

 as the quantity of alumina requisite to produce the same effect ; 

 the same thing would hold in the sulphates, nitrates, and all the 

 other genera of salts. Three times as much potash would be 

 required to saturate 100 sulphuric, nitric, or any other acid, as 

 would be requisite of alumina. 



These facts explain how it happens that when two neutral 

 salts decompose each other, the new-formed salts are also 

 neutral, and why there is no excess of acid or base upon the one 

 side or the other. The same |)roportions of bases that saturate a 

 given weight of one acid, saturate all the other acids ; and the 

 same proportions of acids that saturate one base saturate all the 

 other bases. Hence, numbers may be attached to each acid and 

 base indicating the weight of it, which will saturate the numbers 

 attached to all the other acids and bases. This is the founda- 

 tion of Dr. WoUaston's sliding rule of chemical equivalents. 



