When I was younger, I was a Synchronized Swimmer. As a Synchronized Swimmer, you have to fix your hair so there is no movement as you are performing your routine. Knox Gelatin was our secret to getting our hair to stay in place. There were added benefits of using the product, our hair was silkie smooth and so luxuriously soft.
You will need two packages if your hair is longer than over your shoulders. One cup of hot water per package. Stir it until you feel it getting thick, and then pour it all over your hair. You will need a towel to wrap around you shoulders. I like to wet my hair, and put it up in a bun or a makeshift bun before I pour it over my hair. It seems to stick better to the hair when it is already wet. If you are doing this yourself, go slowly, so that none of the gelatine goes to waste.
I leave mine in for as long as possible. I would say the minimum would be about an hour. You will have to shampoo a couple of times to get all the gelatin out of your hair. Believe me, you are going to love it!