LABBOX KJD20, User Manual, Page: 9 / 21

9
Back View (Fig. 4):
Fig. 4. Back view
14. Power switch 15. Power cord socket 16. Fuse device
The power cord can be plugged into the power cord socket (15). The blown fuse can be replaced in
the fuse device (16) (There is a spare fuse in the fuse socket). Slide the power switch (14) to turn on the
instrument.
VI. Sample Preparation
1.Solution
Copper sulfate (CuSO
4
·5H
2
O )
Potassium sulphate (K
2
SO
4
)
Vitriol (1.8419g/L )
2. Procedure
Weight 0.2-2 g solid sample or 2-5 g semisolid or take 10-20 mL liquid sample (around 30-40 mg
Nitrogen), then put it into a digestion tube, adding a catalyzer tablet and heating the sample in the
Kjeldahl Digestor, when the substance is carbonized completely and there is no foam, heat the liquid
to low boiling and keep it, until liquid turns to clear and blue-green. Then heat 0.5-1 h continually.
When the digestion is finished, cool it. At the same time, do the blank test.
VII. Operation Instruction
1. Preparation of the Chemical Reagent
(1) Add distilled water into the distilled water bottle (with a blue label marked with “H
2
O”) a nd then
tighten the bottle cap.
(2) Prepare the sodium hydroxide solution (NaOH ) (concentration: 30
％～
40 %), add it into the
alkali solution bottle (with a yellow label marked with “NaOH”) and then screw the bottle cap firmly.
(Concentration of 35 % is recommended because the solution with this concentration is not subject to
the crystallization and does not cause the pipe clogging when the room temperature fluctuates.)
(3) According to the need of experiment, use Bromocresol Green/Methyl Red Indicator.
(4) Prepare the boric acid (H
3
BO
3
) with a concentration of 2 %, and then add Bromocresol Green/Methyl Red
Indicator at the proportion of 100:1. After they are well mixed, pour the solution into the boric acid bottle (with
a red label marked with “H
3
BO
3
”), and screw the bottle cap tightly.