As Ty re-entered the room, he immediately saw Jack was about to pour the test tubes into the beaker together. Before Ty could do anything, the chemicals reacted exactly the same way as they had last time, exploding everywhere, and of course all over Jack. Even Chelsea and some of the other lab tables were splashed, though with a very minor amount.
Jack's hand was of course, drenched in the liquid, though Ty knew from experience it wouldn't be for that much longer. Quickly grabbing some paper towels, he rushed over and attempted to clean up, but by the time he had gotten there, he saw that most of Jack's hand was once again clean. Which meant that any second now...
All of a sudden, Jack slowed down considerably. Looking at him closely, Ty could see he was a bit flushed and trying to act normal, but something was definitely off. Ty knew Jack had gotten more of a dose than Ty had, and he had more than doubled his cock size. That meant Jack was headed into really big territory.... Ty looked down. Jack was wearing basketball shorts, and Ty could already see what looked like an erection in his shorts, though it was fast growing. Ty raised his hand for the teacher "Can I take Jack to the chemical showers to clean him off?". Barely looking over, the teacher nodded, still concentrated on the spill.
Jack was in his own world. The sensations from his engorged cock rubbing against the fabric of his shorts was giving him so much pleasure he could barely process anything, so Ty pulled Jack up. He could already see the bulge had grown significantly since he had looked at it just a few seconds ago.
Pulling Jack to the back of the room, Ty hoped no one else had seen it. Well he could always wish that they forgot, he mused. Either way, no way to fix now. Closing and locking the door, Ty didn't even bother with the shower, instead simply leaving Jack standing in a daze in front of him.
And continue it did. As Ty watched, Jack's cock reached the same size as Ty's - which meant it had to be longer than a foot soft! It looked like Jack was hiding an enormous cucumber and two softballs in his shorts. And it was still growing! As Ty watched, the head of Jack's cock actually grew out of the bottom of his shorts, lengthening to his knee and then past it a bit. By the time it finally stopped lengthening, the tip of Jack's cockhead dangled dangerously close to the floor.
Ty marveled at just how potent the reaction really was. Jack's cock had to be over two feet long, though it was still (relatively) thin. Jack's balls had also swollen up even more - each one rivaled a watermelon in terms of size.His underwear had long since given up, ripping off and floating to the floor, and his shorts were barely stretchy enough to cover his balls, let alone his firehose penis.
Ty didn't want to change Jack back, but he could make his life easier. Experimentally, Ty wished Jack's underwear to be repaired, and to be modified with a special pouch to support Jack's enormous cock. Then he wished Jack would believe he always had a giant cock. Finally he walked a still-dazed Jack back out to the classroom.