256 HYDROCYANIC ACID. 



faurocerasi, they must first be mixed with ammonia, 

 then with nitrate of silver, and lastly with nitric acid. 



If hydrochloric acid be contained in the solution, 

 together with hydrocyanic acid, they are both precipi- 

 tated from a weighed portion of the solution by nitrate 

 of silver, and the precipitate weighed upon a filter 

 dried at 120. Another weighed portion of the solution 

 is mixed with solution of borax and evaporated to 

 perfect dryness. In this way, all the hydrocyanic acid 

 is volatilized, and the hydrochloric acid converted into 

 chloride of sodium. The dry residue is dissolved in 

 water, the solution acidulated with nitric acid, and the 

 chlorine precipitated by nitrate of silver. 



Another method, which may be executed with great 

 rapidity, and suffices for the determination of the hydro- 

 cyanic acid in any solution, whether bitter almond- 

 water or laurel-water, &c., or for ascertaining the quan- 

 tity of cyanogen in crude cyanide of potassium, depends 

 upon the circumstance that 1 equiv. of cyanide of 

 potassium forms, with 1 equiv. of cyanide of silver, a 

 soluble compound which is not decomposed by an ex- 

 cess of alkali, but from which nitrate of silver precipi- 

 tates the cyanide, or if a little solution of chloride of 

 sodium be previously added, the chloride of silver. 

 The weighed solution, containing hydrocyanic acid is 

 mixed with solution of potassa till it has a strongly 

 alkaline reaction, and a standard solution of silver is 

 then added till a permanent precipitate begins to ap- 

 pear. 1 equiv. of silver employed in the standard 

 solution corresponds exactly to 2 equivs. of hydro- 

 cyanic acid. 



Ten grms. of pure silver are dissolved in nitric acid, 

 the solution evaporated to perfect dryness, and diluted 

 with so much water, that the whole solution may 

 occupy 1000 cub. cents. 100 cub. cents, of this solu- 

 tion, which contain therefore 1 grm. of silver, repre- 



