94 M. Hess on the Scientific Labours of Richter. 



which I have used was pure. He had prepared this salt by 

 dissolving the natural carbonate ; the object in question then 

 was to know if it did not contain lime or barytes. He finds 

 that a solution of strontian is not troubled by adding a solu- 

 tion of ferrocyanate of potash, whilst the least portion of 

 lime or of barytes may be discovered by this means. In its 

 turn lime is distinguished from barytes by the solubility of its 

 sulphate. This work has been quite forgotten, and in our 

 time a chemist in high esteem at Berlin again takes up the 

 question, and supported by more recent works gives absolutely 

 the same solution of the problem which his countryman Rich- 

 ter had given so long before (Pogg., Ann. vol. xliv. p. 445*). 



Richter rinds that it is difficult to prepare very concentrated 

 nitric acid because of the great quantity decomposed by heat. 

 Now this inconvenience is remedied by using a quantity of 

 sulphuric acid double that necessary for decomposing the 

 nitre. Richter proposes another means which merits our at- 

 tention ; he adds to the nitre one-third of its weight of per- 

 oxide of manganese, and the quantity of sulphuric acid neces- 

 sary for decomposing the two substances. He finds that the 

 disengagement of oxygen which accompanies the distillation 

 of nitric acid prevents the formation of nitrous acid. 



It was already known in Richter's time that salts while 

 passing from the state of solution to that of crystals, gave out 

 heat. The same phenomenon takes place when water becomes 

 ice ; it was therefore thought fit to indicate the analogy of the 

 two phenomena by saying ice of crystallization, instead of 

 water of crystallization, the term which had been used till then. 

 Richter puts the question, whether water which is found com- 

 bined in crystals exists in them in the state of ice or not. 

 This is the manner in which he succeeds in solving this in- 

 teresting question. He dissolved 1440 parts of crystallized 



sulphate of soda (NaS + 10H); the temperature of which 

 was 15°*55 C. in 3405 parts of water, the temperature of which 

 was 76 0, 67 C. The solution obtained indicated a tempera- 

 ture of 48°*96. Supposing that the capacity of the elements 

 for heat remains the same, Richter finds that 



1440 . 15-55 + 3405 . 76'67 



—r-rz = 58'4 



4845 



should be the temperature of the liquid. There is therefore 

 a lowering of temperature of 9°'44. He admits that the spe- 

 cific heat of the liquid was 0'75, and that consequently the 



[* A translation of the paper (by H. Rose) here referred to will be found 

 in Phil. Mag. S. 3. vol. xiv. p. 78.— Edit.] 



