The American saw the first large billow of greenish-yellowy mist that rolled from the open door, and followed.
The hall-porter was closing his office for the night when Elk appeared, hatless and breathless.
“Can you ’phone the flats?—good! Get on at once to every one on and below the third floor, and tell them on no account to open their doors. Tell ’em to close all cracks with paper, to stop up their letter-boxes, and open all windows. Don’t argue—do it! The building is full of poison gas!”
He himself ’phoned the fire station, and in a few seconds the jangle of bells sounded in the street outside, and men in gas-masks were clattering up the stairs.
Fortunately, every tenant except Broad and his neighbour was out of town for the week-end.
“And Miss Bassano doesn’t come in till early morning,” said the porter.
It was daylight before the building was cleared by the aid of high-pressure air-hoses and chemical precipitants. Except that his silver was tarnished black, and every window glass and mirror covered with a yellow deposit, little harm had been done. A musty odour pervaded the flat in spite of the open windows, but later came the morning breeze to dispel the last trace of this malodorous souvenir of the attempt.
Together the two men made a search of the rooms to discover the manner in which the gas was introduced.
“Through that open fireplace,” Elk pointed. “The gas is heavier than air, and could be poured down the chimney as easily as pouring water.”
A search of the flat roof satisfied him that his theory was right. They found ten large glass cylinders and a long rope, to which a wicker cradle was attached. Moreover, one of the chimney-pots (easily reached from the roof) was scratched and discoloured.