153 § 92. SPECIAL METHODS OF ANALYSIS. 



the red color by adding the permanganate solution from 

 the burette as before. The permanganate added this time 

 is consumed in oxidizing, not only the 10 c.c. of oxalic 

 acid that was added to the solution, but also other organic 

 matter, and therefore more permanganate will be required 

 than Avhen the oxalic acid was mixed with distilled water, 

 as in the first experiment. Multiply the number of milli- 

 grammes of permanganate in this additional quantity of 

 the solution used, by 5, for the organic matter, expressed 

 in milligrammes. The determination is only an approxi- 

 mate one, since different kinds of organic matter require 

 difi*erent amounts of oxygen for their complete oxidation, 

 while in the above estimation it is assumed that the same 

 amount is consumed by the same quantity of organic mat- 

 ter of whatever kind. 



92. Estimation of Sulphur {and Chlorine) in Organic 

 Compounds. 



Fuse 2 parts of a mixture of i^ure caustic potassa 

 free from sulphuric acid (or chlorine) Avith ^|g part of pure 

 potassic nitrate in a silver dish, with the addition of a 

 little water. When the mixture is cold, add 1 part (3 to 

 4 grms.) of the finely pulverized substance, fuse the 

 whole with constant stirring with a silver spatula, and 

 continue the application of the heat until the mass has 

 become quite white ; if it does not readily become so, a 

 little more potassic nitrate may be added. 



Dissolve the fused substance in dilute nitric acid, evap- 

 orate to dryness, and eliminate silica (§ 58, c?, 1), and in 

 the filtrate from this, precipitate the sulphuric acid, into 

 which the sulphur in the original substance has been con- 

 verted by oxidation, with baric chloride (§ 59), or with 

 baric acetate, if chlorine is to be determined in the filtrate 

 from the baric sulphate ; the chlorine in this filtrate is 

 precipitated by argentic nitrate (§ 63, ci), 



93. Separation and determination of Potassium^ Sodi- 



