sure inside the system is equalized by 

 manipulating the mercury reservoir 

 and the evolved volume of carbon 

 dioxide gas is read from the graduated 

 glass reservoir tube. A correction is 

 made for the water vapor pressure in- 

 cluded in the barometric pressure and 

 then connected pressure, room tem- 

 perature and evolved gas volume are 

 combined with the sample weight to 

 calculate the carbonate content. 



Organic nitrogen^ 



Reagents : 



1. O.OIN hydrochloric acid - 0.86ml. 

 hydrochloric acid is added to about 

 950 ml. of distilled water in a 

 volumetric flask and standardized 

 against the dried sodium carbonate 

 solution. Water is added until the 

 normality of the acid is 0.01. 



Z. O.OIN sodium hydroxide solution - 

 a concentrated carbonate -free 

 solution of sodium hydroxide is 

 prepared by dissolving an equal 

 weight of sodium hydroxide in 

 water and then placing the 

 stoppered mixture in a water bath 

 at 80° C. for 12 hours. One-half 

 ml. of the clear supernatant liquid 

 is then pipetted into about 900 ml. 

 of freshly boiled water. This is 

 standardized against the hydro- 

 cloric acid using methyl red indi- 

 cator. ,^ 



3. Sodium carbonate solution - 0.0250 

 gm. of sodium carbonate which has 

 been dried in an oven at 250 C. 

 for 2 hours is added to 50 ml. of 

 distilled water. This is boiled and 

 then titrated against the fresh 

 hydrochloric acid solution using 

 methyl orange indicator in order 

 to determine the normality of the 

 acid. Weighing of the carbonate 

 should be done as carefully and 

 accurately as is possible. 



4. Methyl red - 0.15 gm. of methyl 

 red is treated with 40 ml. of sodium 

 hydroxide solution and then stored 

 in a glass stoppered bottle. 



Procedure : Samples are powdered 

 and dried overnight at 105° C. After 



.cooling, 0.200 gm. of the sample is 

 placed in a Kjeldahl flask together 

 with two Hengars granules and 3 ml. 

 of concentrated sulfuric acid. The mix- 

 ture is heated gently initially and then 

 over a strong flame for a total of 1 5 

 minutes. After cooling slightly, three 

 drops of 30 percent hydrogen peroxide 

 are added and heating resumed for 

 another 10 minutes. If the solutions 

 are not clear amber or pale green in 

 color, then three nnore drops of peroxide 

 are added and heating resumed. The 

 cooled sample solutions are then washed 

 into a steam distilling unit of the 

 Kjeldahl type and mixed with 15 ml. of 

 40 percent sodium hydroxide. The two 

 solutions are mixed and the resulting 

 ammonia distilled over to the acid trap 

 by steam drive. The evolved gas is 

 passed through a carefully measured 

 10-ml. volume of O.OIN hydrochloric 

 acid. Ten minutes of distilling are 

 usually sufficient. The acid solution 

 is then brought to boiling and back- 

 titrated with O.OIN sodium hydroxide 

 to a clear pale orange end point using 

 three drops of methyl red indicator. 



Organic carbon'' 

 Reagents: 



1. Potassium dichromate solution - 

 19.61 grns. of potassium dichro- 

 mate (K2Cr207) are ground and 

 dried at 110°C. After cooling in a 

 desiccator, the reagent is dis- 

 solved in water and made up to 1 

 liter in a volumetric flask. 



2. Ferrous ammonium sulfate solu- 

 tion - 78.6 gms. of ferrous ammo- 

 nium sulfate are dissolved in water 

 containing 20 ml. of sulfuric acid 

 and made up to 1 liter in a volu- 

 metric flask. This solution should 

 be standardized frequently as it 

 deteriorates in the presence of air. 



3. Diphenylamine - 0.5 gm. of di- 

 phenylamine is dissolved in 100 ml. 

 of concentrated sulfuric acid. This 

 is then poured slowly into 20 ml. 

 of cold water. 



Procedure : A large pyrex test tube 

 is cleaned and dried and 10 ml. of 



FoUouiiis X'iederl and Niederl, 1947 



* Following Allison, 1935 



15 



