How do you know if you're getting the right deicer? Check for labeled contents. Unfortunately, many times no information is provided. Some suppliers sell anhydrous calcium chloride- an excellent deicer- with the very misleading label "contains no calcium chloride."
Or, check some things for yourself. Add a little sodium hydroxide to a concentrated solution of the deicer (CAUTION). It an ammonia-like odor results, get an assurance form the seller or manufacturer that the product is not ammonium nitrate or sulfate. If you have a chemist friend, have him add barium chloride to a solution of the deicer, as slightly acidified with hydrochloric acid. An immediately formed white precipitate indicates substantial amount of sulfate, and that's probably bad.
Chloride salts are indicated if a copious white precipitate is formed when a dilute silver nitrate solution is added to a solution is added to a solution of the deicer slightly acidified by dilute nitric acid. Urea is indicated if a little of the deicer in a spoon melts and then volatilizes when held over a flame.
Positive test don't necessarily eliminate the negative but they do normally indicate that the deicer is satisfactory for use. If the deicer isn't urea or a chloride salt, consult an expert before using.