'Well, the class seem fairly advanced for their level. ... Though I would question whether it is advisable to teach them a potion like the Strengthening Solution. I think the Ministry would prefer it if that was removed from the syllabus.'
-- Dolores Umbridge to Snape (OP17)
Unknown, but presumably increases the user’s physical or magical strength.
salamander blood, possibly pomegranate juice at some stage
References from the canon
- Apparently takes a few days to make, since the students had allowed their mixtures to mature over a weekend (OP17).
- The fifth year students were making this when Umbridge evaluated Snape. She said that she thought the Ministry would prefer that it be removed from the syllabus (OP17).
- Harry was so interested in watching Snape and Umbridge interact that he nearly put pomegranate juice into his potion when he should have been adding salamander blood. The fact that the pomegranate juice was laid out at all suggests that it might also be an ingredient of this potion, although Harry was attempting to add it in the wrong way at that particular time. At the end of the lesson, when his potion was congealing foully and smelling strongly of burned rubber, Harry was given a homework assignment of writing an essay on how and where he went wrong (OP17).
During Order of the Phoenix, Snape seems ambiguous to many readers - yes, he's in the Order and visits Grimmauld Place, but he's also being rough with Harry during Occlumency lessons and gives him extra homework. But in the case of the Strengthening Solution scene, a clue is the way he turns around and stares at Umbridge when she tells him the Ministry would want him to stop teaching that potion. And when Harry's potion turns out to be a mess, Snape makes sure he will learn how to make it in spite of Umbridge by setting him an essay for homework before she has time to ban it from his class. In hindsight it's clear all the way through that Snape was only doing what Dumbledore expected of him, whether spying for the Order, or teaching an unwilling Harry a potion to make him stronger.