270] Analysis of Portion Soluble in HCl 161 



basin, and allow it to stand for half-an-hour in the balance 

 case. Then weigh out portions as follows : 



(a) 5 grams in a platinum dish ; 



{p) 5 grams in a pair of watch glasses with clip ; 



(c) 5 grams in a wide-mouthed 4-oz. beaker. 



Treat the different portions as follows. 



N.B. — Each of the following operations occupies a consider- 

 able length of time ; it is, therefore, best to get them all started 

 as nearly together as possible, so that no time may be wasted. 



(a) Determination of moisture plus organic matter and salts 

 of ammonia. Place the dish containing the weighed portion 

 of soil on an Argand which has its flame turned down very low. 

 Turn up the flame very gradually, about once every five minutes, 

 until in an hour it is about as hot as when used for turning 

 calcium oxalate to calcium carbonate. The soil will turn darker 

 in colour, and then slowly lighter, as the carbonised organic 

 matter is burned off. In order that all the hot soil may be 

 exposed to the air it is necessary to stir it occasionally. To 

 do this use a piece of No. 10 B.W.G. copper wire about 

 4 inches long, having one end flattened out for about § inch. 

 See that the wire is polished, and free from any roughness 

 which may cause the soil to adhere. With this instrument 

 a little care will enable the operator to stir the powder without 

 causing any loss whatever. At least five hours will be required 

 for the complete oxidation of the organic matter. When that 

 time has elapsed, cool the dish in a desiccator and weigh, then 

 return to the Argand for half-an-hour. Repeat the process 

 until no further loss is sustained. After the burning has been 

 completed, this portion is treated with HCl and used for the 

 general analysis (see paragraph 271). 



The reason for keeping the temperature below a red heat is 

 to prevent the decomposition of the CaC0 3 . 



M 



