Well, is it translucent and liquid or coloured with some fruity smell (sometimes they mix it with this purple syrup but there are other flavours too). That would definitely tell you if what you have is pure injectable or a mix. At my vet they take the 50mg/ml and dilute it down to 12.5mg/ml with some sort of sweet syrup. I don't think I would ever be able to get a rat to take undiluted injectable orally ... although the advantage is that the dosage is minute.
Then there's always the taste test (though I warn you, if it is the pure injectable, you may feel like puking after not even a drop). I once accidentally got some on my hand (I had to inject the Batryl on a rat who was dealing with a nasty pneumonia) and got it in my mouth and dear god! I don't know what drain cleaner tastes like but now I can imagine. I gained a lot of empathy for my rats that day let me tell ya. Whereas the diluted stuff is far more "tolerable" and the banana suspension (why that thing isn't more prevalent I don't know ... the 50mg/ml is a godsend .. you barely have to give any and the rats love it) is quite tasty.
