The drug is phenobarbital , 24mg is the dosage but pills come in 15 and 30mg. It is one of those drugs where 2mg either way can do nothing or do harm. It isn't soluble in water , pediatric dosages used ethanol but not going that route , just too iffy.
I have been able to cut 30mg into quarters so roughly 3 pieces is 22.5mg but if the cut isn't perfect and she gets less than that she seizes and a really sad sight ,she just stops walking, stares, then starts jerking with her mouth clenched open and falls over convulsing, last about 2 minutes , then she opens her eyes and stumbles around, doesn't want to be held or touched for about 5 minutes.
I,m going to see if I can get a beam type scale until I can find another solution. Me , the SO, and our dog Charlie really appreciate all the suggestions.