Limestone is by definition a rock that contains at least 50% calcium carbonate in the form of calcite by weight. All limestones contain at least a few percent other materials. These can be small particles of quartz, feldspar, clay minerals, pyrite, siderite and other minerals.
Answers (4) You have not mentioned the name of the medicine in your post. Ideally 4 times a day means every 6 hours. It depends on what the medicine is as to how rigid you should be in regards to dosing. If the medicine is an antibiotic then every 6 hour dosing is important as is pain relief medication if in severe pain. If the dosing isn't so critical then 4 times a day could be evenly spaced out during the waking hours.
1 If it bothers your stomach, try taking it with food.  Bactrim can be taken at any time of the day; however, be sure to take the medication at the same time(s) each day. For instance, if you take it twice daily, it is best to evenly space the doses, taking a dose every 12 hours.