Abstract: In the filling of small-bore tubing with a gas under conditions such that the purity of the gas is maintained during the filling operation, a pump-head having large interior and exterior conduits connectable to a high-speed high-vacuum pump provides for rapid evacuation. The tubing can be heated for removal of traces of oxygen-containing contaminants from the interior thereof. Filling is effected by means of small-bore tubing; a valve-plug permits sealing-off of the major portion of the interior conduit so that the volume of the gas remaining in the interior of the pump-head subsequent to the filling operation is small. The pressure in glass tubing is reduced below atmospheric by immersing the tubing in a suitable chilling mixture, thereby making it possible to seal off the tubing by heating it to fusion and allowing it to collapse. The tubing to be filled with gas may be held in a casting which fits to the pump-head sealingly.