Heavy liquids – eg Bromoform

[Tim StevensParticipant @timstevens64731]

I am trying to identify a special heavy liquid (called Hobson's K-S liquid) used in some old car petrol gauges. There are several possibilities including Bromoform, Methylene iodide, Acetylene tetrabromide, Barium Mercuric Iodide, and various fancy salts of Thorium and Tungsten. They all sound pretty horrid, but are used to identify gemstones by density, for instance.

The same stuff might just be used in older aeroplanes, I suggest. So, any ideas?

[Tim StevensParticipant @timstevens64731]

[Keith LongParticipant @keithlong89920]

Tim – try following this link it should take you to a downloadable pdf and I think the info you're after is on page 25. It looks as though the fluid could be available from folk who stock spares for old (1930s) Fords, I've seen references to suppliers in the USA but I don't know whether you'd be able to get it over here though.

[martin perman 1Participant @martinperman1]

Tim,

What do you need the liquid for, is it to dampen the movement of the needle. If yes why not use Glycerine as used in Hydraulic pressure gauges.

Martin P

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by martin perman on 11/10/2017 13:11:30:

What do you need the liquid for, is it to dampen the movement of the needle. If yes why not use Glycerine as used in Hydraulic pressure gauges.

It's used in a U-tube manometer to measure the pressure at the bottom of the petrol tank so needs to have the correct SG. The instrument was called a Hobson Telegauge. A google search for Hobson Telegauge fluid comes up with a number of suppliers. No idea what it consists of though. I did have some some years back from my car restoring days but can't find it now.

Russell

[Norman BillinghamParticipant @normanbillingham91454]

acetylene tetrabromide and 1,1,2,2-tetrabromoethane are synonyms for the same compound, the latter being the modern name. Unusual stuff because it's very dense (nearly 3g/ml). As Keith says, there's a US supplier on ebay but nearly £50 including postage for 30 ml and I don't know about how they could ship it. I'd try Sigma Aldrich – they list it for £24 for 250g (+vat etc). Whether they will sell to a private citizen I don't know – you can only ask. Handle carefully – it's not all that nice.

[Neil WyattModerator @neilwyatt]

Seems to be a lot of information online if your search "Hobson K-S petrol telegage".

It seems the original fluid is tetrabromoethane.

Neil

[Tim StevensParticipant @timstevens64731]

Thanks, everyone. Indeed, I am researching Hobson's Telegage (their spelling) and the fluid for it. I did a brief search on Bromoform, but I guess that this is either another name for something else, perhaps even tetrabromomethane, or is so nasty that even mentioning it brings the Elvan Safe Tea to the door.

I will now go and do a more informed search, and write in the margin of my book the current recommendation.

I get asked all sorts of odd questions at club nights, and I try to give answers that make sense.

Regards

Tim

[Tim StevensParticipant @timstevens64731]

The way many needle-type instruments are damped is either by an aluminium disc in a magnetic field (eddy currents) or by using a small cup with a thick (viscous) silicone fluid. Sometimes both. Perhaps I was taken as using the term 'heavy' in the oil viscosity sense when I meant the density sense.

If so, I am no better than All-bran, who claimed 'It keeps you regular' when they meant 'It keeps you frequent'.

Cheers, Tim

[Neil WyattModerator @neilwyatt]

'Bromoform' is the bromine form of chloroform, CHBr3.

Neil

[Martin DowingParticipant @martindowing58466]

Pure compounds of this type are easily identifiable.

Methylene Iodide like to solidify just below RT and it smells very similar to bromoform which smells similar to chloroform but its boiling point and density is much higher.

Mercury iodide is very difficult soluble solid – it won't be there and barium Iodide is solid but will form very heavy liquid once dissolved in water. This solution mix with water but bromoform, methylene iodide or tetrabromoethane does not do so. Mercury or barium iodide do not have smell unless partially decomposed – then there might be faint iodine smell

Forget tungsten, thorium or uranium compounds (mainly halides) – they are not there. Very reactive, corrosive and are reacting with water violently.

If not miscible with water measure boiling point (boil it in conical flask with termometer above liquid level), check if it solidify in fridge and in freezer (may take few days, shake flask vigorously once cold to speed process up), describe smell and will give you idea.

Hydrohalocarbons (tetrabromoethane, bromoform or methylene iodide) are not flammable and they are miscible with petrol, acetone or ethanol.

Of course it might be mixture of few compounds.

Tertabromomethane (carbon tetrabromide, not to be confused with tetrabromoethane) is solid.

Regarding safety of halocarbons – politically correct assesment is "very dangerous, cancerogenic ozone depletors blah blah blah…" but practically only slightly harmful compounds. Was working with all of them in the lab, breathed vapours because fumecupboard was working poorly, poured over my hands on number of occassions, nothing happened. My former boss is over 80, was doing it whole life – nothing happened.

Mercuric iodide or barium iodide are in practice moderately toxic – very difficult to absorb toxic quantity not deliberately. Poliitically correct peoples are calling them to be very or extremely toxic, but then powderized dried roots of A. napeallus (monkshood) common in English gardens would be *extermely extremely toxic*, so it is best not to abuse meaning of words.

I would pay a bit of respect to tungsten, thorium or uranium halides due to their great chemical reactivity (would dissolve or rather decompose skin or eye tissue nicely).

Edited few times for clarity

Martin

Edited By Martin Dowing on 11/10/2017 18:41:23

Edited By Martin Dowing on 11/10/2017 19:03:01

Edited By Martin Dowing on 11/10/2017 19:05:56

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