Does it come with a dropper attached to the inside of the top? If not you might wanna score one of those things somewhere, there are eye- or nosedrops that have a bottle that can be opened, although some other types are impossible to open without breaking it. If you do that, rinse the hell out of the bottle with eye- or nosedrops, to be sure and use distilled water for that the last few times. Then of course dry it off a bit and pour your liquid acid in, carefully! Shame to spill it, and if you accidentally wipe your face and ingest it you could start tripping accidentally.
Hits are not very meaningful standards for doses, I guess what is more or less meant is that one hit is supposed to give you a medium experience. Decent liquid acid should have a dosage of around or over 100 ug per drop, but of course there is more potent stuff out there.
From a dealers point of view, he may sell you hits and charge prices per hits, but they are not full doses so that he makes more money. So it depends on the relationship with your source.
The volume (in ml - milliliters indeed) is not really important because if you use a dropper then the volume of the drop is what is important.
What you can do to test, once you get a bottle or vial with a dropper on top, is get it empty and then add 50 drops of distilled water using the dropper. Use a marker to draw a line at the level of the liquid. Then clean well, and put your LSD in. It should go to the same level. Of course you can also just drop your liquid acid in there 1 by one and count the drops.
Also, if you liquid acid smells of alcohol (so that is the solvent for the LSD), then you need to test the volume of 50 drops with alcohol as well because the drops do not have an equal size.
Be careful with tap water, it destroys your LSD.
There is also a possibility that allows for more accurate measurement and no dropper. Buy an oral 1 ml syringe that has 10 bars drawn on it. No needle required. Every bar is then 0.1 ml
Get a bottle, preferably of amber / dark color in which 5 ml will fit. If your LSD liquid solution contains no alcohol you might want to buy everclear alcohol (ethanol) or vodka. I think during the making process of vodka there is enough time for the chlorine to get out naturally. Otherwise get a type made from spring water or whatever. Anyway if your liquid LSD is dissolved in alcohol, just add distilled water until you reach a total of 5 ml in your bottle. The other way around, if the LSD is dissolved in water, add alcohol. The end result should be at least 20-25% strong (that is 40 proof to 50 proof I guess). Now using the syringe you can take out 0.1 ml with significantly better accuracy than a drop, and dose yourself.
Depending on how much experience you have, trying a full hit of a new batch may not be the best idea, I'd probably just try half of that to test the waters, then either redose >2 hours later or take a full hit another time. At least then you get 50 hits out of it for sure and you know what that guy meant by a hit.