The Fertilisers (Sampling and Analysis) Regulations 1996

14a. METHOD FOR THE APPLICATION OF THERMAL CYCLES

SCOPE

1.  This method defines the procedure for the application of thermal cycles before carrying out the oil retention test on straight ammonium nitrate fertilisers containing more than 28% nitrogen by weight.

FIELD OF APPLICATION

2.  This procedure is for thermal cycling prior to determining the oil retention value of the fertiliser.

PRINCIPLE AND DEFINITION

3.  Heat the sample in an Erlenmeyer flask by immersing the flask in a water bath at 50° C and maintain at this temperature for two hours (phase at 50° C). Then cool the flask in a water bath at 25° C and maintain at this temperature for two hours (phase at 25° C). The combination of the two phases, first at 50° C then at 25° C, forms one thermal cycle.

APPARATUS

4.  Normal laboratory apparatus, in particular

4.1  Water baths thermostated at 25 (+1) and 50 (+1)° C respectively.

4.2  Erlenmeyer flasks with an individual capacity of 150 ml.

PROCEDURE

5.  Place each test sample of 70(+5) grams into an Erlenmeyer flask which is then closed with a stopper. Place the flask in the 50° C water bath for 2 hours, then transfer to the 25° C bath for a further 2 hours. Transfer the flask back into 50° C water bath for a further 2 hours and then return to the 25° C bath.

Maintain the water in each bath at constant temperature, stir fairly rapidly and ensure that the water level is above the level of the sample in the flask. Protect the stopper from condensation by a rubber cap or aluminium foil.

After two thermal cycles, keep the sample at 20+3° C for the determination of the oil retention value.