510 REPORT— 1878. 



fined to the estimation of caustic alkalies, nobody would, in the author's opinion, 

 think of using it in preference to the process commonly used ; but he wished to 

 show that it might with great advantage be applied to the determination of alka- 

 line carbonates. From 0'5 to 1 gramme of the potassium or sodium carbonate should 

 be dissolved in about 100 c.c. of distilled water, the solution mixed with an excess 

 of hydrocyanic acid (10 to 20 c.c. of acid of Scheele's strength ), and then deci- 

 normal solution of silver nitrate added from a burette until a permanent opalescence 

 is produced. The reaction occurs in accordance with the following equation : — 



K 2 0O s + 2HOy + AgN0 3 = KAgCy 2 + KNO s + 00,. 



The first drop used in excess causes a precipitation of silver cyanide. "Whereas 

 under ordinary circumstances hydrocyanic acid is incapable of decomposing alka- 

 line carbonates, it effects a complete decomposition in the presence of silver nitrate. 

 The mixture does not require boiling, and the whole operation may be performed 

 within a few minutes. 



If after the end of the titration the mixture is boiled, and the addition of 

 decinormal solution of silver nitrate proceeded with, this time using potassium 

 chromate as an indicator, the volume of silver solution required to ensure complete 

 precipitation of the silver cyanide will be exactly equal to that used in the first 

 titration. 



KAgCy, + AgNO s = 2Ag0y + KN0 3 . 



This second reaction might then, if desired, be used as a check on the determi- 

 nation. In the presence of chloride, the volume of silver solution used in the 

 second experiment will be greater than that used in the first, the difference between 

 the two being exactly that required to precipitate the chloride. In this manner a 

 determination of the chloride might be readily combined with that of the alkaline 

 carbonate. 



The following results were quoted to show the great accuracy of the process : — 



Pure Potassium carbonate used Carbonate found 

 0-5850 0-5851 



0-1670 0-1G72 



0-8775 0-877!) 



Mixtures of pure potassium carbonate and sodium chloride : — 



Used Found 



fK 2 C0 3 0-2000 0-2005 



NaCe 0-0680 0-0683 



K,C0 3 0-9750 0-9750 



NaOe 0-1825 0-1830 



The author gives the following reasons why for. the essay of samples of potash or 

 soda he considers this process as better than the one usually employed : — 



1. The solution does not require boiling, and the operation therefore requires less 

 time -than the usual process. 



2. The change from absolute clearness to an unmistakable turbidity as produced 

 by a single drop of the reagent is more striking than that of the colour of litmus 

 brought about by a drop of normal sulphuric or hydrochloric acid. 



3. The test solution being a deci-normal one, the results obtained are more 

 accurate than those obtained with standard normal mineral acids. 



4. With but- little additional trouble, and without having to operate on fresh 

 sample, the process may be readily coupled with an accurate determination of the 

 chloride present in the alkaline carbonate. 



In concluding, Mr. Siebold stated that he was at present engaged in experiments 

 showing a still wider range of useful applicability of this process ; and that the re- 

 sults of these experiments he hoped to be able shortly to lay before the Chemical 

 Society. 



; SATURDAY, AUGUST 17, 1878. 

 The Section did not meet. 



