Messines ridge

[Muerrisch]

as a matter of interest the Fauld crater fits the theoretical RE calculations rather well: the maths works on small and big 'oles.

[Guest]

I have heard differing opinions as to the stability of the explosives in the 'Missing Mine'-some people have told me that ammonal becomes less likely tro go off with age, others the reverse.

I am assuming that there are no detonators in place, as these would have been inserted shorly before the mine was due to be detonated.

The problem with ammonal is that it is TNT with ammonium nitrate and aluminium added.

The aluminium acts to slow down the speed of detonation and increase the lifting effect. It is used for this purpose in a range of commercial explosives.

The ammonium nitrate is basically a bulking agent which, added to high explosive, makes what you have go further. It is also used in amatol, a WWII mortar bomb filling, and in many of the large improvised explosive devices made by terrorists, where it needs a good quality high explosive as an initiator and needs to be mixed with various other substances.

Ammonium nitrate can simply leech out, but under the right conditions, it can also form sensitive crystals which can be initiated by friction. One of the standard inspection points in amatol filled 3" mortar bombs was to check for AN crystals in the fuze cavity threads.

So, no telling, except that after 90 years the TNT may be OK, but the AN may not.

[Max Poilu]

As far as I understand the explosives used are reasonably stable. Wet Guncotton is relatively safe and can be sawn, drilled or hit with a hammer - these are High Explosives and need a considerable detonation force to trigger them. Ammonal (a mixture of 65% Ammonium Nitrate, 17% Aluminium, 15% TNT and 3% Charcoal) is less safe.

Guncotton (formed by the action of Nitric and Sulphuric acids on cellulose - cotton wool or similar and then pressed and dried in blocks) was able to be used wet and in this manner actually produces more explosive force. It is harder to detonate and in this scenario a primer of dry guncotton is used, itself triggered by a conventional fulminate of mercury detonator. There is a block of this explosive in the La Targette museum, it looks like a small flat brick with a central hole.

Early mines were charged with 100 lb bags of black powder. According to A. Barrie (War Underground) later mines used 50 lb boxes of Ammonal sometimes supplemented with Guncotton and occasionally Blastine. This was detonated with 25 lb primer charges fitted with electrically fired detonators. Considering some of these mines had more than 50 000 lbs of charge that is a lot of boxes!

Spanbroekmolen was charged with 1800 sealed tins of Ammonal, and at 91 000 lbs they must have been large tins...

I believe the largest mine was produced by the Canadians at St Eloi with a charge of 95,600 lbs of explosive 125 feet down.

Many of the charges were contained in waterproof bags clamped with wooden battens at the top. A friend in France has one of these immaculately preserved with Gov. arrow and date. Apparently there is a very large supply available when his colleague gets the time to recover them.......

The really unstable explosives left as a legacy of the Great War are mainly shells charged with Picric Acid based explosives which form highly un-stable compounds by reaction with the metal casing.

[Tom Morgan]

Thanks, Pals, for the interesting technical info.

Tom

[KONDOA]

Guncotton (formed by the action of Nitric and Sulphuric acids on cellulose - cotton wool or similar and then pressed and dried in blocks)

Leave out the Nitric acid and you have cigarette filters!!

I have just built a machine making this filter stuff in one of the original factories that made gun cotton.

Roop

[Bob Coulson]

"Gentlemen I do not know whether we shall change history tomorrow but we shall certainly alter the geography"

Maj-Gen Sir Charles Harington June 6th 1917.

Bob.

[Howard]

With all this discussion about explosives, perhaps it is worth mentioning the Royal Gunpowder Mills at Waltham Abbey. During the Great War there were 5000 people working there making explosives for the Western Front.

www.royalgunpowdermills.com/

As their website says, they do not open again until next April but they have interesting exhibits including descriptons of ammonal, TNT etc.

It is an interesting place, much of it derelict and a large amout more suitable for birdwatchers than Great War researchers, but worth a visit.

Howard