Sorry to dredge up such an old thread but I've recently got my hands on some AH.
It is a strange compound indeed; I find if I cook it up and leave it to cool (in the cooker) it doesn't re-solidify, despite cooling quicker than when surrounded with insulating plastic. Maybe it's something in the plastic that it causing it to fall out of solution? I'd test the hypothesis but the only glass syringe I have is an emergency naloxone one. Even after rinsing fifty times I wouldn't want to accidentally naloxone myself.
I find the best way to keep it in solution is to use 2ml (well really 3; the markings go out to 2.5 but it says 2ml on the packs) syringes filled up to 2.5. Use about 0.2-3ml of prop glycol (go to your baking aisle and it should be there in the food flavourings (mainly, with a little water, alcohol and flavour in very small amounts) as preservative (and to increase the volume), make sure to read the ingredients and if there are a few different ones with PG in them give them a shake; the one with the slowest rising bubbles will have the highest concentration. I find rum flavouring works the best (and you get an awesome rum taste when shooting benzos). Now before you tell me that shooting food flavouring is extremely dangerous, it is food grade PG. Much less chance of contaminants of bench grade PG so unless you go and buy 99.99% analytical grade, it's going to be safe. After the prop glycol is tossed in a few grains of citric should be added, much less than you would use for H. Now what you're going to want to do is get a hairdryer and your plastic syringe, turn it on and use it to warm the syringe up. use the hairdryer as far away as possible from your AH in it's spoon/cooker unless you want to be scraping it off the walls, having the AH on top of a desk and the dryer under will isolate the airflow. Now that your syringe is hot to the touch (but not melting or distorting in shape) you can cook the AH. If you can always hit a vein first time then the hairdryer need not be used, it's just to stop the AH cooling below body temp to room temp.
I find that 100mg/1.125ml is the golden ratio for liquid (PG included in this final number, just half the above), it will start to solidify in the syringe but only when the liquid drops below body temp. Unless you're shooting boiling hot water don't worry about vein damage, that will do much more damage than AH that solidifies above body temp in a syringe. This is because blood is mostly water and red blood cells once you get it into a vein (remember to drop your tourniquet to keep the blood flowing) the AH will be quickly dissolved into pints of blood.
As for it being caustic; I've not noticed this. One thing I have noticed is a burning (almost like I need to cough) feeling in my lungs after shooting this, though mephedrone and MDMA do this too.
I'd type up a bit more but it's 7am here. I need to get some sleep. Watch this space; I may well return to edit.