Found a little piece about it here, using caffeine to lower the H temp huh ? interesting, I don't understand 90% of it though, anyone care to give a quick run down ?

"According to Klous et al Diacetylmorphine is available as the free base and as the hydrochloride salt. The latter is theoretically less suitable for inhalation after volatilisation, since it has a higher melting point (243–244 ◦C) than the free base (173 ◦C)

Klous et al found that when heroin is combined with caffeine as an excipient, the melting point and boiling point is lowered:

The main effects of the addition of caffeine to diacetylmorphine base seemed to be the formation of a eutectic mixture with a 14 ◦C lower melting point and increasing volatilisation rates for mixtures with larger proportions of caffeine

They also found that adding caffeine increases the recovery of diacetylmorphine HCl and diacetylmorphine base after volatilisation and reduces degradation upon heating. As they point out, this is similar to the practice of cutting illicit heroin with caffeine, and illicit heroin is often vapourised on foil at user-controlled temperatures (achieved by duration of heating and distance of flame).

I'm not sure what effect the use of glycerides such as propylene glycol as an excipient would have on the melting point and volatilisation of heroin, maybe it would be similar to that of caffeine.

I've been trying to find accurate information on the internal operating temperature of e-cigs, but so far without luck. I also wonder if the presence of caffeine in the Brown used by zefix might have been a factor in his successful experiment. Maybe it would be worth adding caffeine to illicit heroin before mixing with proplyn glycol or e-juice.

Source:

Thanks to AltrdPerception for the link to this document; Pharmaceutical heroin for inhalation: Thermal analysis and recovery experiments after volatilisation Klous et al 2005.