HYDROCYANIC ACID. 255 



carbonate of soda, 5 grms. of nitre, and 20 grms. 

 of decrepitated chloride of sodium, and the mixture 

 heated to redness in a platinum crucible. When cool, 

 the mass is dissolved in water, the solution slightly 

 acidified with nitric acid, and the sulphuric acid pre- 

 cipitated by chloride of barium. (See No. 3.) 



The amount of carbon may be inferred by differ- 

 ence. In order to determine its quality, and to ascer- 

 tain whether it has been completely or incompletely 

 carbonized, the mixture of sulphur and carbon is 

 boiled with a solution of protosulphide of potassium, 

 which dissolves the sulphur, leaving the carbon, which 

 must be well washed and dried. The sulphide of 

 potassium should not contain any free potassa, since 

 this might dissolve an imperfectly carbonized char- 

 coal. Bisulphide of carbon may also be employed for 

 the extraction of the sulphur. 



The sulphur as well as the coal may be completely 

 oxidized by boiling with a solution of permanganate 

 of potassa. The oxide of manganese is after wards, dis- 

 solved by hydrochloric acid, and the sulphuric acid 

 precipitated by chloride of barium. 



126. HYDROCYANIC ACID. 



In order to determine the strength of a solution of 

 pure hydrocyanic acid, a weighed quantity of it is 

 treated with solution of nitrate of silver, which is 

 added gradually, and with frequent agitation, until no 

 further precipitation takes place, and the odor of 

 hydrocyanic acid has entirely disappeared. 



The precipitated cyanide of silver is collected upon 

 a filter (previously dried at 120 and weighed), washed, 

 dried at 120, and its weight determined. 



For the estimation of the amount of hydrocyanic 

 acid in the aqua amygdalarum amararum and aqua 



