Subject: Re: Schoniger flask - purpose?
From: email@example.com (Don Wilkins)
Date: Sep 08 1996
On 7 Sep 1996 09:42:11 -0400, firstname.lastname@example.org (JohnP99978) wrote:
> I am reviewing a method to determine inorganic ions. This particular
>method recommended the use of a Schoniger flask for sample preparation
> Could someone describe this type of flask? What is its purpose? Are
>there any recent articles or references for this flask for further
>reading? What is CONTRAD 70 solution?
Never heard of Contrad 70 solution but then Alzheimers does take its
The Schoeniger flask is named for the developer of the procedure:
Professor Wolfgang Schoeniger, a very competent microanalyst.
The original was nothing but an Erlenmeyer flask and it was used for
determining elements in organic compounds. Specifically chlorine but
also adapted for other elements.
1. One Erlenmeyer flask (actually more than one because they exploded
2. One (one hole) rubber stopper for the flask. (Reusable after the
3. One glass rod with a platinum coil at the end stuck through the
one hole rubber stopper so that when the stopper was inserted into the
flask the Pt coil was a couple centimeters above the bottom. (Usually
reusable after explosions)
4. Supply of oxygen gas.
That answered all of your questions except for references but I
suppose you would like to know how to risk life and limb with that
collection of stuff.
1. Add a few ml of dilute NaOH to a clean flask.
2. Weigh a few milligrams of sample onto a small piece of ashless
filter paper. (Use the good stuff that has a low blank but determine
what the blank is.) If you weigh too large a sample then be certain
that extra flasks are available.
3. Fold the filter paper around the sample and place the folded paper
in the Pt coil.
4. Fill the flask with oxygen.
These next steps should be done rapidly with no hesitation between
steps. You might want to make a few practice runs before wasting a
5. Ignite the folded paper, insert the flaming paper into the flask,
secure the stopper by pressing firmly, invert the flask so the
solution forms a seal, shield eyes with other hand and grit your
6. If everything goes right you will get a clean burn and a bit of
white ash will slowly drift down.
7. Shake flask for a few minutes to absorb chloride e.g. and proceed
Sometimes things don't go as planned. So if:
A. Black unburned material is present go back to step one.
B. Flask explodes.
1. Dry off and go back to step one.
2. Remove shards of glass, dry off, and go back to step one.
3. Remove shards of glass, dry off, explain procedure to technician
and leave room during analysis.
The analysis was first done on the lab bench with no concern for
safety as described and I have seen Professor Schoeniger analyze a
sample in a lecture hall. At that time some safety barriers were used
but the explosion will leave a ringing sensation in your ears for a
long time. As people pushed the sample size it became apparent that
some precautions were in order. The laboratory supply houses saw an
opportunity for earning a dollar and the apparatus became available
commercially complete with safety shields, mechanism for inverting the
flask, and would you believe remote ignition of the sample after
ignition. Isn't progress wonderful?
Now for you young'uns that procedure for analyzing organic compounds
for chloride might not be a big deal but you should keep in mind that
this simple procedure replaced combustion procedure using a Parr Bomb*
containing several grams of sodium peroxide. Professor Schoeniger
would complete a chloride analysis in a few minutes in a lecture hall
but in the lab the analysis required several hours of work. It was
Professor Schoeniger was a skilled and resourceful analytical chemist.
The references will be found starting about 1953-4 and continue for a
few years. You probably will find most in Z. anal. Chemie as he was
either Swiss or German. Unfortunately he met an untimely early death
and the analytical community lost a skilled researcher.
*I never could understand why the Parr company used the word <bomb>
instead of <pressure vessel>.
From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Subject: Re: Schoniger flask - purpose?
Date: Tue, 10 Sep 1996 18:17:13 LOCAL
In article <email@example.com>
firstname.lastname@example.org (Don Wilkins) writes:
>On 7 Sep 1996 09:42:11 -0400, email@example.com (JohnP99978) wrote:
>> I am reviewing a method to determine inorganic ions. This particular
>>method recommended the use of a Schoniger flask for sample preparation
>> Could someone describe this type of flask? What is its purpose? Are
>>there any recent articles or references for this flask for further
>The Schoeniger flask is named for the developer of the procedure:
> Professor Wolfgang Schoeniger, a very competent microanalyst.
>The original was nothing but an Erlenmeyer flask and it was used for
>determining elements in organic compounds. Specifically chlorine but
>also adapted for other elements.
The Quickfit Catalog calls it Schoniger, and references
A.M.G.MacDonald in Analyst v.86 p.1018 ( 1961 )
[ Wonderful entertaining, nostalgic commentary deleted ]
Yes, and the most common variant in the petroleum industry
moved from a 500ml conical flask to a 1 litre flat-bottomed
round flask = bigger bangs...
I've used the technique for sulfur, chlorine and phosphorus
contents of a whole range of petroleum products, and it
definitely is one of the more fun analyses - watching the
paper burn so brightly.
>Sometimes things don't go as planned. So if:
>A. Black unburned material is present go back to step one.
>B. Flask explodes.
C. Paper burns in wrong places and falls into the solution,
( very common in our lab ).
D. Stopper leaks ( after a while the ground glass joint tends
to distort slightly )
>Now for you young'uns that procedure for analyzing organic compounds
>for chloride might not be a big deal but you should keep in mind that
>this simple procedure replaced combustion procedure using a Parr Bomb*
>containing several grams of sodium peroxide.
The method became the standard method for S, Cl, P
in mineral oils. It could be quick - about 30 mins for
two. I think it is still used - The methods I followed
were either ASTM or IP ( Institute of Petroleum = UK ),
the IP method numbers were 242, 244, 245 - from
The technique is often just called flask combustion,
rather than oxygen or schoeniger flask combustion.
Parr bombs are OK, but bonb calorimeters are also
fun - they come with a 10 metre extension lead
for the ignition switch ( for the fainthearted/sensible
souls who wanted to stand in the next laboratory ).