Subject: Smoke bombs
Date: 30 May 90 16:15:01 GMT

>It also said that smoke bombs should be bought, because they were too difficult
>and dangerous to make.  Seems like I've heard several easy and foolresistant
>ways to make smoke-generating mixtures, though now that I think of it none of
>them included an oxidizer--they were just supposed to burn.  Is adding an 
>oxidizer the dangerous part?
Smoke bombs usually do not contain any strong oxidizer and the mixtures
are seldom able to explode violently. However, some of them may self-ignite
and still be dangerous in that respect.

I can remember only a few effective and relatively safe mixtures, more can be
found in the pyrotechnics literature. Both of the following mixtures are based
on zinc. 

1. A stoichiometric mixture of zinc powder and hexachloroethane. This mixture
is very easy to ignite and gives a lot of grey and bad-smelling smoke. The
mixture also burns quite fast as an loose powder, but the burning rate can be
reduced by pressing the mixture to a hard "cake". This mixture is also
relatively unstable. The hexachloroethane sublimes even at room temperature 
and is volatilized in few weeks or months, if the mixture is not kept in a 
tight container. If the mixture gets some moisture, the zinc will start reacting
slowly and if the charge is great enough, it may self ignite.                                                  

2. A stoichiometric mixture of hexachloroethane, zinc oxide and aluminum dust
- much safer, but requires a pyrotechnic igniter charge. Black
powder will do just fine, if it is slow burning (no gunpowder FFFF!). A gram of 
potassium nitrate-magnesium will ignite the stuff even better. This mixture is
used in smoke grenades and cans and it can be stored for a few years without
significant deterioration.(In tight cans). This also gives grey smoke and is
slightly more efficient than the previous one.

In the first mixture zinc can be substituted for magnesium, and the mixture
will become even more unstable.

There are also numerous chemicals, that fume on exposure to air. To mention a
few: titanium, tin and silicon tetrachlorides, phosphorus trichloride,
chlorosulphonic acid, sulphur trioxide. All of these are hydrolyzed by the
moisture in the air and create a mist of hydrochloric/other acid and a
metal/other oxide. Just spray them in the air and you get a very dense, white 
smoke. As a drawback, half of the smoke is extremely corrosive acid.... Not 
to be recommended for household use, outdoors only! :-)

A mixture of potassium chlorate with ammonium chloride and sugar also generates
smoke when burned, but is hazardous to use and even more dangerous to store. 
Chlorates should never be mixed with ammonium salts, since ammonium chlorate is
very unstable. This recipe can still be found in some pyrotechnic books; be
careful, if you try this or at least use it immediately after preparation.