PNEUMATIC TOOLS 281 POACHING under pressure is conducted to the tool by a hose. Percussion Tools. — Tools of this tyi)e are the air hammer, clippers, chippers, caulkers, balast tappers, riveters, etc. The action in all is essentially the same. Air, under pressure of 85 to 100 pounds per square inch (except in the case of riveters where it is under higher pres- sure) is sent into a cylinder containing a piston, which is made to reciprocate in the cylinder by proper valve action, the tool is supported in the front end of the cylinder, and transmits the blow received from the piston to the work. George Law, an Englishman, invented the first pneumatic tool, a percussion rock drill, in 1865. In this tool, as in most which have followed, the opposite end of the drill from the tool end was fitted with a handle and a controlling throttle. Boyer of St. Louis, Mo., invented the chipping hammer in 1896, and in 1899 Keller brought out the first valveless hammer, in which there is no valve be- yond the position of impact, while the valve hammers are fitted with a recipro- cating valve which regulates the inlet and exhaust of the driving air. Modern engineering has introduced many im- provements and refinements and many patents have been issued on various meth- ods of actuating and controlling the de- vice. In general the valve type has a longer stroke, and a more powerful blow than the valveless type, while the latter operates at a much higher rate of speed, sometimes over 20,000 strokes a minute, and it is claimed (which claim is not uncontested) by some engi- neers that valveless types have a much longer life and are less liable to get out of order. The percussion tools vary in size from a small hand hammer to the large stationary plate riveter weigh- ing tons. Rotary Tools. — The principal rotary pneumatic tools are the drills, reamers, etc. They are made in a great range of sizes, and are used for many things, such as drilling wood and metal, reaming boiler tubes, grinding valve seats and cylinders, polishing and grinding. The rotary tools usually operate under a pres- .sure of about 75 pounds per square inch. The motor may be of the rotary type or of the reciprocating type with either fixed or oscillating cylinders, operating on a crank shaft to which the tool is fastened by a suitable mechanism. The great demands on the part of the shipyards for pneumatic tools of all t3T>es at the time of the World War gave even greater impetus to the already great and fast growing industry of manufacturing pneumatic tools. PNEUMOCONIOSIS, affection of the lungs arising from occupation in a dust- laden atmosphere. It takes a form of chronic bronchitis, with the develop- ment of a catarrhal condition and par- tial pneumonia, shrinking and coloring the tissues. Among stone cutters the disease is known as phthisis, and amonp coal miners as anthracosis. Its mani- festations vary with the occupation, but the mortality is heavy in all. PNEUMOGASTRIC NERVE, a nerve, called also par vagum, which, proceeding from the neck to the upper part of the abdomen, supplies branches to the phar- ynx, oesophagus, stomach, liver, spleen, and respiratory passages. PNEUMONIA, inflammation of the lung, usually caused by exposure to cold or wet, a cold draught or chill after be- ing over-heated, injury to the chest, ir- ritation, or as a secondary affection in smallpox, typhoid or puerperal fever, and other low wasting diseases; it may also be caused by long continued congestion of the lung substance, particularly in heart disease, or in old and weak people who are bedridden from any cause. Pneumonia terminates generally in reso- lution and recovery, but sometimes in death from collapse and exhaustion. PO, the largest river of Italy, rises on Monte Viso, one of the Cottian Alps, at an altitude of 6,405 feet, ciose to the French frontier. It flows E. for upward of 20 miles, when, arriving before Saluz- zo, it emerges from its rocky d^ftles and enters upon the plain. From Saluzzo it flows N. N. E. past Turin to Chivasso; there it changes its course toward the E., in which direction it flows to its em- bouchure in the Adriatic. Upward of 55 miles from its mouth, above Ferrara, it begins to form its delta, 60 miles wide from N. to S. The delta is rapidly grow- ing in area. Ravenna, a city once on the seashore, now stands 4 miles inland. The Po receives from the left the Ticino, Adda, Mincio, and other streams and from the right the Trebbia and others. It has an entire length of 360 miles, and drains an area of nearly 28,900 square miles. POACHING, the trespassing on an- other's property for the purpose of kill- ing or stealing game o! fish. Accord' ing to the law of England, when a per. son's land adjoins a stream where there is no ebb and flow that person is as- sumed to have an exclusive right to fish in the stream as far as his land extends, and up to the middle of the stream; and so also when a person's land incloses a pond, the fish in that pond belong to him. Where several properties are con"
