If the break is very close to the stopcock, very little reheating and blowing can be done, on account of the danger of getting the stopcock sleeve out of shape, and the work must be heated very slowly to prevent cracking.
"Laboratory Manual of Glass-Blowing"
Francis C. Frary
The whole apparatus being strapped upon my back, I was enabled to direct a stream of powerful precipitating gas in any desired direction, the flow being under control through the agency of a small stopcock.
"Humorous Ghost Stories"
Dorothy Scarborough
Many laboratories in this country, especially in the west, are located a long way from any professional glass-blower, and the time and money spent in shipping broken apparatus several hundred miles to be mended could often be saved if some of the laboratory force could seal on a new stopcock, replace a broken tube, or make some temporary repairs.
"Laboratory Manual of Glass-Blowing"
Francis C. Frary