G. S. Jamieson — Determination of Mercury. 349 



Art. XXXI. — A New Volumetric Method for the Determina- 

 tion of Mercury ; by George S. Jamieson. 



Among the methods that have been proposed for the volu- 

 metric determination of mercury, the titration in nitric acid 

 solution by means of ammonium thiocyanate,* according to 

 Volhard's method for silver, while it appears to be very accu- 

 rate, is not generally applicable because it cannot be used in 

 the presence of chlorides. The method of Euppf consists in 

 adding potassium iodide and an excess of sodium hydroxide to 

 any mercuric solution, then precipitating the finely divided 

 metal by means of formaldehyde, and, after acidifying with 

 acetic acid, dissolving the metal with standard iodine solution 

 and titrating back with sodium thiosulphate. This method is 

 simple and rapid, and while it seems to be a good one for 

 small quantities of mercury, my experience with it is that it 

 gives seriously low results with amounts of mercuric chloride as 

 large as 0*1 to 0'2 grams. Hempel's method, J which consists 

 in titrating mercurous chloride (or iodide) with iodine and thio- 

 sulphate, is undoubtedly very accurate, if it is used with 

 proper precautions to completely dissolve the mercurous chlor- 

 ide in the iodine solution. § 



The method to be described is based upon the titration of 

 mercurous chloride with potassium iodate in the presence of 

 15 to 20 per cent of actual hydrochlori ^cid and ''a small volume 

 of an immiscible solvent, such as ctuxoform. This general 

 method of titration is the well known one of L. W. Andrews, || 

 but as far as is known it has not been applied previously to the 

 titration of mercurous chloride. It has the advantage over 

 Hempel's method in requiring only a single, very stable volu- 

 metric solution, instead of two solutions which cannot be pre- 

 served for a long time unchanged, while the method of titra- 

 tion appears to be no less exact. It is to be observed that the 

 iodate titration cannot be applied to mercurous iodide without 

 the employment of an entirely different factor, since the iodine 

 would affect the results. 



It has been found that mercurous chloride reacts with potas- 

 sium iodate according to the theoretical requirements of the 

 equation 



4HgCl + KI0 3 + 6HC1 = 4HgCl 2 + KC1 + IC1 + 3H 2 



* Cohn, Berichte, xxxiv, 3502 : Kupp, ibid., xxxv, 2015. 



flbid., xxxix, 3702. 



X Sutton, I0th edition, p. 263. 



^ Smith, Chem. News, cv. 14. 



j| Jour. Amer. Chem. Soc.', xxv, 756, 1903. 



