The crowd indicated where it ought to be—­it was Stacey’s.  Firemen and policemen were entering the huge building.  McCormick shouldered in after them, and we followed.

“Who turned in the alarm?” he asked as we mounted the stairs with the others.

“I did,” replied a night watchman on the third landing.  “Saw a light in the office on the third floor back—­something blazing.  But it seems to be out now.”

We had at last come to the office.  It was dark and deserted, yet with the lanterns we could see the floor of the largest room littered with torn books and ledgers.

Kennedy caught his foot in something.  It was a loose wire on the floor.  He followed it.  It led to an electric-light socket, where it was attached.

“Can’t you turn on the lights?” shouted McCormick to the watchman.

“Not here.  They’re turned on from downstairs, and they’re off for the night.  I’ll go down if you want me to and—­”

“No,” roared Kennedy.  “Stay where you are until I follow the wire to the other end.”

At last we came to a little office partitioned off from the main room.  Kennedy carefully opened the door.  One whiff of the air from it was sufficient.  He banged the door shut again.

“Stand back with those lanterns, boys,” he ordered.

I sniffed, expecting to smell illuminating-gas.  Instead, a peculiar, sweetish odour pervaded the air.  For a moment it made me think of a hospital operating-room.

“Ether,” exclaimed Kennedy.  “Stand back farther with those lights and hold them up from the floor.”

For a moment he seemed to hesitate as if at loss what to do next.  Should he open the door and let this highly inflammable gas out or should he wait patiently until the natural ventilation of the little office had dispelled it?

While he was debating he happened to glance out of the window and catch sight of a drug-store across the street.

“Walter,” he said to me, “hurry across there and get all the saltpeter and sulphur the man has in the shop.”

I lost no time in doing so.  Kennedy dumped the two chemicals into a pan in the middle of the main office, about three-fifths saltpeter and two-fifths sulphur, I should say.  Then he lighted it.  The mass burned with a bright flame but without explosion.  We could smell the suffocating fumes from it, and we retreated.  For a moment or two we watched it curiously at a distance.

“That’s very good extinguishing-powder,” explained Craig as we sniffed at the odour.  “It yields a large amount of carbon dioxide and sulphur dioxide.  Now—­before it gets any worse—­I guess it’s safe to open the door and let the ether out.  You see this is as good a way as any to render safe a room full of inflammable vapour.  Come, we’ll wait outside the main office for a few minutes until the gases mix.”

It seemed hours before Kennedy deemed it safe to enter the office again with a light.  When we did so, we made a rush for the little cubby-hole of an office at the other end.  On the floor was a little can of ether, evaporated of course, and beside it a small apparatus apparently used for producing electric sparks.