Page:Popular Science Monthly Volume 88.djvu/691

 Popular Science Monthly

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��Reverses Tug's Propeller- Blades

WITH small boats, the quickest and surest way to back-water is to reverse the pitch of the propeller-blades. Numerous motor-boats are equipped with mechanism which performs the task by the mere shifting of a lever, but in the case of larger craft the blades of the propeller are so heavy that to reverse them by an ordinary lever would be al- most impossible. A large tug that plies San Francisco Har- bor was recently equipped with a propeller -blade re- versing mechanism, which, while embodying the old lever principle, accomplishes its purpose in a surer and more ingenious way.

The blades are shifted by levers that are controlled by a worm-gear, which is in turn operated by a hand-wheel and chain. When the wheel is spun, the worm revolves, causing the levers to be pushed in or out, the pitch of the blades being determined by the direction and number of turns of the wheel. An addi- tional advantage of this type of blade shifter is that the pitch of the blades can be altered, as de- sired, to an almost i n fini- tesimal degree.

��Fumigating Has Improved, But Are We Less Afraid of Germs?

IN these days of sanitary living, sani- tary breathing, sanitary sleeping, san- itary eating, etc., fumigation has come to be one of the most popular of in- door medical sports. Not a great many

���If the pitch of the propeller- blades is reversed, the con- tinued drive of the engine will back the boat. Here is a device which does just this thing with complete mechanical success

����Cyanogen gas carried to your door — or window — to fumigate your house

��years ago, when we were still eating butter that had not previously gone un- der the vigilant microscope of the health officer, we considered that a little block of sulphur burned in a room after someone had had measles would annihil- ate the last germ. Not long ago, how- ever, an enterprising physician some- where in the United States examined a sample of wallpaper that had been on the wall since a case of diphtheria had run its course there a score of years be- fore. On the sample he found an agile, active colony of diphtheria germs. This was not the sole cause, but it was one of the immediate causes of wide-spread, better fumigation.

Cyanogen, deadliest of gases, is now smoked into a room in which patients having contagious diseases have lived. The latest and one of the most effective ways of dealing death to the lurking microbe depends on a tank fastened to the rear of an automobile. The automo- bile is driven up alongside the house to be fumigated, a hose is attached to the top of the tank and led into the room.

Structurally, the automobile fumigat- ing machine is highly interesting. An electric motor, attached to an air-pump, is started in the bottom of the tank, causing air to be forced through the mixture of chemicals.' This air draft carries the death-dealing gases through the tube into the room.

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