310 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



element such as sulphur, instead of with one another. The 

 law of reciprocal proportions suggests that equal quantities 

 of sulphur will combine with 8 parts of oxygen and with 3 

 parts of carbon, or with some simple multiple of these 

 numbers. In practice it is found that 16 parts of sulphur 

 unite with 3 parts of carbon and with 2x8=16 or with 

 3 x 8 = 24 parts of oxygen. 



Like the two preceding laws, the law of reciprocal pro- 

 portions may be interpreted most easily with the help of 

 t)alton's atomic theory. But as an experimental law it 

 had been recognised and used twenty years previously. 

 Thus Cavendish had recognised in 1788 (Phil. Trans., 78, 

 178) that the quantities of nitric and sulphuric acid which 

 neutralised equal weights of potash would also decompose 

 equal weights of marble. The weights of potash and of 

 marble which saturated the same quantity of acid he had 

 described as long ago as 1766 as EQUIVALENT to one another 

 ("On Rathbbne Place Water," Phil. Trans., 1767, 57, 102). 



The law of reciprocal proportions was developed and 

 tested experimentally for a large range of acids and bases by 

 the German chemist J, B. Richter (1762-1807) in his 

 Stochiometry (1792-1794) and in a series of eleven volumes 

 on New Chemical Topics, published between 1791 and 1802. 

 Richter noticed that : 



" When two neutral solutions are mixed, and a decom- 

 position follows, the new resulting products are almost with- 

 out exception neutral also." 



" The elements must, therefore, have amongst themselves 

 a certain fixed proportion of mass" (Stochiometry, I. I24). 1 



Thus muriate of lime and sulphate of ammonia, when 

 mixed together in solution, were changed into sulphate of 

 lime and muriate of ammonia. The sulphate of lime 



1 Quoted from Angus Smith's Dalton and the Atomic Theory (1856), 

 p. 190. In this book, twenty pages are given to translations from 

 Richter's works. 



