killed one batch of yeast

I made a 10gal batch the other day and was off with temp before I put the yeast in. one of my 5 gallon carboys is doing good but the other one is dead in the water. Can I harvest yeast from the good one and how do I go about doing that.

I can't say I've ever been in that situation, so I'm just spit balling here. If you have another 5 gallon container and it has been less than 24 hours after you pitched then rack half of each into the new fermentation vessel, then combine the other two. If it has been more than 24 hours I would be concerned about aeration. If there is a good amount of karousen then you can scoop as much off as possible and move it to the second fermented.

I would just repitch fresh yeast into the dead one if it is truely dead. What was the temp when you pitched the first time?

The one I’m thinking was over 90 which is the problem. Took bad temp reading and thought about it after I poured it in. I do have the equipment for oxygen.

Yeast should be okay at 90 degrees. Many people proof yeast at around that temperature. It sounds like just lag.

over 48 closer to 72. I'm thinking of adding oxygen and siphoning some of the other batch in. Will that work??

If the yeast really is dead you are going to be severely under pitching unless you equally combine the two batches. If fermentation has staredes, but it just isn't visible then aerating now will oxygenate your beer. You could measure the gravity and see if it has started at this point.

new plan I put it the the frig and waiting for new pack. when pack comes take out of frig smack pack wait, then add air and pour in.