18 



METHODS OF ANALYSIS 



[Chap. 



ORGANIC CARBON.— OFFICIAL. 



APPARATUS. 



(a) A calorimeter bomb. — Use a type that permits the recovery and transfer of the 

 entire solid residue of the exploded charge to a small vessel by means of a jet of 

 water. 



(b) Parr's apparatus for determining carbon dioxide — Illustrated in Fig. 2. 



FIG, 2. PARR'S APPARATUS FOR THE DETERMINATION OF CARBON DIOXID. 



This consists of a 150 cc. Erlenmeyer flask {F) fitted with a 3-holed stopper through 

 2 of which the stems of 2 dropping funnels {S) and {A) extend almost to the bottom 

 of the flask. A capillary tube, passing through the third hole and flush with the 

 bottom of the stopper, connects with the gas burette {B). 



(C) A simple Hemple gas pipette. — Contains S0% potassium hydroxid solution. 



6 DETERMIXATIOX. 



Introduce 2 grams of soil as prepared under 2 (1 gram if high in organic matter), 

 0.75 gram of magnesium powder, and 10 grams of sodium peroxid, into the closed dry 

 calorimeter bomb, and mix thoroughly by shaking the bomb back and forth. Explode 

 the charge by means of an electric spark or by dropping a red hot plug into the bomb 

 through an automatic valve which closes immediately after the plug enters. Remove 

 the residue from the bomb, using as little hot water as possible, heat to boiling, and 

 transfer to the receiving funnel (S) of Parr's apparatus. From the acid funnel (A) 

 run 50 cc. of sulphuric acid (1 to 2) into the flask (F). Connect the apparatus and 

 slowly add the contents from the receiving funnel (S). The carbon dioxid gener- 

 ated passes through the capillary tube into the graduated burette (B). Heat the 

 contents of the flask (F) to boiling and boil for 1 minute, then force the gases into 

 the graduated burette {B) by introducing water into the flask (F) through the fun- 

 nel (S). Read the burette, recording the temperature and pressure. Pass the gas 

 into an ordinary absorption pipette containing 30% potassium hydroxid solution. 

 Shake the gas with the solution until carbon dioxid is wholly absorbed. Return the 



