Black Magic is an anthology of short stories ostensibly all dealing with the theme of black magic, forbidden sorceries and texts, voodoo and diabolism. It does fall somewhat short of that, with one story about a mad scientist and another about a vampire. (By Nathaniel Hawthorne and Ray Bradbury, respectively.) However, those are both quite striking stories, so perhaps it's not so bad to break a little from the premise of the collection.
The other stories are grouped into five sections: Devil Worship, Witchcraft, Curses, Magic Writing and Incantation, and Voodoo. As well as the Hawthorne and Bradbury, there's entries from Algernon Blackwood, H. G. Wells, M. R. James, Avram Davidson, and Theodore Sturgeon. Of particular note are James' "Casting the Runes," a nicely atmospheric tale of supernatural vengance, and Davidson's "Where do you live, Queen Esther?," which reflects that author's talent for mixing the fantastic and everyday to stunning effect.
I also quite liked Margaret Irwin's "The Book," a tale of a cursed object leading to a man's doom; the story uses a rather novel approach towards the first symptoms of the curse. Blackwood's "Ancient Sorceries" was nicely atmospheric, though the end explained the strange phenomena in a way that felt a little too pat. (I would have prefered it a little more ambiguous.)
As with all collections, some stories are stronger than others, and if I had to pick a low point, it'd be "Cheese" by A. E. Coppard, which seemed like it should either be funny or scary, but didn't manage to do either quite right.
I wouldn't recommend seeking out the collection, as most of these stories could be found elsewhere. But if you ever run across this little bit of pulp in a used book store, it's definitely worth a look.