378 HISTORY OF SCIENCE. 



constitution of compounds in the ponderable proportions of their 

 constituents. He nowhere, however, formulates the law of definite 

 proportions. It is not improbable that the defects in the methods of 

 quantitative analysis used by the chemists of Lavoisier's time prevented 

 the constancy of the proportions in which substances combine from 

 emerging from the analytical results as the absolute law. We can 

 hardly wonder at doubts and denials of the idea of fixed proportions 

 arising in the minds of chemists of that time, when we find one of the 

 most skilful (Berthollet) determining by an experiment that 100 parts 

 of sulphuric acid contained 69 of sulphur and 31 of oxygen, and by 

 another experiment that the proportions were 72 of sulphur to 28 of 

 oxygen. 



About the time, however, that Lavoisier was laying the foundations 

 of modern chemistry, two comparatively unknown German chemists 

 experimentally established the fact of definite proportions, and, be- 

 sides, introduced a new conception into the science, namely, that of 

 equivalents. WENZEL, of Freiburg, published in 1777 a treatise on 

 chemical affinity. He explained the fact of two neutral salts forming, 

 by interchange of acids and bases, two new salts, also neutral a cir- 

 cumstance which had struck the chemists of that time. This fact may 

 be illustrated thus : If a solution of sulphate of soda is mixed with 

 one of nitrate of lime, there is immediately produced sulphate of lime, 

 which falls to the bottom of the vessel as a white powder, and also 

 nitrate of soda, which remains in solution. The exchange of acids and 

 bases which takes place in this action may be illustrated by this dia- 

 gram, where the names of the products are printed in italics. 



Sulphate of Soda. 

 Sulphuric Acid. Soda. 



/ 



Nkric Acid. Lime. 



Nitrate of Lime. 



The noticeable thing was that whatever quantity of lime left the nitric 

 acid to unite with the sulphuric acid, replaced just so much soda as 

 was able to perform with the nitric acid the same function of forming 

 a neutral salt. There was also the like reciprocal equivalence of the 

 acids. It is easy to mix the solutions in such proportions that all the 

 sulphuric acid and all the lime are both precipitated ; and from the 



