Scientific Analytical Calorimeter Solutions

How to Handle Difficult Samples


A difficult sample is one which causes grief. This is indicated when:

The results are not consistent.
The sample doesn’t ignite
The CAL3K issues warnings
When a warning is issued then the unit has found some measurement outside the expected range. If the displayed message is not understood then press F10 and check if it explains the warning better. If this is still a mystery then drink a coffee and contact the factory with the error code.

What Causes the Inconsistent Results

We discount hardware, weighing and preparation errors. In all instances the result is lower than expected. This is so because the CAL3K can lose energy but cannot gain it. Three possible scenarios can cause a lower result.

The vessel O-ring (s) have leaked. This can be checked by re-inflating a vessel after the determination. If it fills then the bomb has leaked. Replace all the O-rings. It is also possible that the bomb leaked just after firing. The pressure inside the bomb increases to about 60 to 90bar (depending on the burning speed) and the O-ring may leak during this high-pressure period. Reduce the filling pressure to 20bar and try again.
Part of the sample are ‘scattered’ by a violent burning (explosion). They are now on the inner vessel walls. Check with a clean paper towel. If sample material is found then:
  • Press the sample in to a tablet. If not possible then
  • Reduce the filling pressure or
  • Place the sample in to a gelatin capsule. This is called ‘spiking’ and the CAL3K can handle it.
Part of the sample is lying in the crucible (raw or glazed over). Increase the filling pressure or put a good burning substance next to the sample. This is called ‘spiking’ and the CAL3K can handle it.

Why is the Sample Not Igniting

The CAL3K indicates a MISFIRE and has terminated the determination. This can have many reasons and here is what should be checked:

The CAL3K indicates a MISFIRE! If the cotton is still hanging on the firing wire, then a short exists for the firing current and the wire is not heated. Change center top O-ring.
If the cotton is lying in the crucible, then the bomb had no oxygen
If the cotton is gone but the sample is intact then the cotton has not touched the sample or the sample didn’t ignite. If the cotton has touched the sample material, then the problem is in the sample: it is reluctant to burn! The solution is spiking. The spike material heats the sample so that is will burn.


Most of the above solutions are straight forward. The spiking procedure is explained in the manual and is an easy solution.

The CAL3K handles the standard and the EASY spiking and calculates the net result.

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