86 M. Hess on the Scientific Labours of Richter. 



that considerations of another order, supported by decisive 

 experiments, seem to enable us to appreciate his ideas pro- 

 perly. 



Before Richter, and in his time also, it was supposed that 

 the affinity of a substance was in the direct ratio of the quan- 

 tity necessary to saturate another body. Richter compares 

 the quantities of tartaric and of acetic acid necessary to satu- 

 rate the same quantity of lime. He finds that more tartaric 

 acid is necessary, and concludes that its affinity is greater, 

 and that consequently this acid should displace acetic acid. 

 He makes trial of this, and really it is tartaric acid which 

 seizes the lime and displaces the acetic acid. Few examples 

 are found more suitable than this for characterizing the dif- 

 ficulties which are met with every day in chemistry, for here 

 is a well-observed fact, a conclusion drawn ; an hypothesis 

 follows, then comes the experiment which confirms it. You 

 believe your principle well established ? By no means. An- 

 other fact comes and overturns it. Subsequently Richter 

 again takes up the question, and this time he clearly proves, 

 that affinity is not exerted in the ratio of the masses which com- 

 bine. — Vol. x. p. 187-195. 



It is in the fourth volume (viertes Stuck, 1795) that Richter 

 establishes truths which will always be reckoned amongst the 

 most important acquisitions in the region of the exact sci- 

 ences. He begins by researches on the capacity of saturation 

 of hydrofluoric acid; for this he uses several bases, and does 

 not neglect alumina. He tells us (p. 10) that he took 650 

 grains of very pure carbonate of alumina, which he saturated 

 with hydrofluoric acid. Here then is what he is accused of, 

 for carbonate of alumina does not exist ! The parenthesis, then, 

 where he says that 1000 parts of this alumina contained 542 

 of pure alumina, has not been read. Nor have his calculations 

 been followed, for he everywhere takes into account alumina 

 at the rate of 542 parts for 1000. All of you, gentlemen, who 

 addexperience to a general knowledge of chemistry, will know 

 that it is very difficult, I may say almost impossible, to obtain 

 pure alumina ; if we precipitate it from its solutions by the car- 

 bonate of ammonia, it always retains a little of this salt, and 

 water besides. It is only by calcination that we can obtain it 

 really pure ; but then it becomes difficult to dissolve in acids. 

 This, doubtless, is the reason why Richter used non-calcined 

 alumina, and determined by a separate experiment the real 

 amount of that earth which it contained. 



After having found the quantity of different bases by which 

 1000 parts of hydrofluoric acid were saturated, a verifi- 

 cation is required. For this purpose he decomposes fluoride 



