Seliwanoff's test for carbohydrates determines if sugars are aldose sugars or ketose sugars, according to Reference.com. The difference between the two is that ketose sugars have a ketone group while aldose sugars have an aldehyde group.
Reference.com goes on to explain that during the test, resorcinol and hydrochloric acid are used as reagents. The ketose sugars and aldose sugars are heated, and the ketose sugars, because they dehydrate at a faster rate than aldose sugars, turn a bright red. Aldose sugars turn a light pink color.
The University of Calgary points out that the difference between ketose sugars and aldose sugars is part of the chemical formula. Aldose sugars have a single bond between a carbon atom and a hydrogen atom and a double bond between that hydrogen atom and an oxygen atom. Ketose sugars have a double bond between a carbon atom and an oxygen atom. Glucose is an example of an aldose sugar, and fructose is an example of a ketose sugar. Sucrose tests positive as a ketose sugar because it is made up of both fructose and glucose.
Wikipedia explains that Theodor Seliwanoff, after whom the test is named, was a Russian chemist who lived between 1859 and about 1921.