40s or 50s scifi short story contact with alien spaceship

I'm trying to remember the title and author of a short story I read years ago. It concerned a deep space exploration ship that comes upon an alien ship. The alien crew is in hibernation. The investigating crew wants to salvage the ship because it is made up of all sorts of exotic materials never seen before. A lowly ensign shows that it can't be salvaged because the materials are unstable at warmer temperatures. He took shaving from the ship and put them in a rescue flare and the contents explode when it warms up. I think the ship was described as sort of fish shaped with the drive engines in the nose.

Any clues?

Markf