The need for a n accurate method of determining t h e velocities of moving gases in pipes and flues is receiving increased attention from the marine and mechanical engineers, and i t is a need which has long been felt by t h e chemical and metallurgical engineers, b u t has been somewhat neglected by them. Gases are used as raw materials, or appear as either intermediate or final products, in many chemical and metallurgical processes of manufacture. Undoubtedly, in such processes, an accurate

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... ans of measuring gas velocities would lead t o the prevention of much loss and waste, through t h e substitution of known facts for guess-work. For example, wherever air is used under pressure, as in the copper blast furnace or t h e copper converter, a knowledge of the amount of air used, in comparison with t h e theoretical amount required, would in many cases lead t o a reduction of air, and so of power, wasted. I n t h e sulfuric acid industry, where gas is diverted t o two or more absorption towers connected in parallel, a knowledge of t h e velocity, and hence of t h e quantity of gas going t o each tower would lead t o a proper adjustment of dampers so as t o secure equality of distribution and more economical operation. I n suits for damages claimed t o have been caused by obnoxious fumes escaping from t h e flues of industrial works into t h e atmosphere, t h e substitution of knon-ledge as t o t h e quantity of escaping fumes, for estimates and guesses, would eliminate legal controversies. The business of selling natural gas and manufactured gas for power. heating and lighting, demands an accurate means of measuring the velocity of flow, in order t o properly affix costs and selling prices. I n designing t h e equipment of chemical and metallurgical plants, some means of calibrating the capacities of blowers and ventilating machines, vacuum pumps. aspirators, etc., would enable engineers t o check up t h e claims of manufacturers of such equipment, and would prevent t h e installation of inefficient devices, as well as t h e financial losses involved thereby. Other examples of t h e value of a reliable means of measuring t h e velocities of gases will occur t o t h e reader. Georg Lunge statesz t h a t as early as 1866 Fletcher's modification of Peclet's differential anemometer was described. This is in effect a crude sort of pitot tube. The velocity of t h e gas was calculated on t h e basis of t h e difference between t h e pressures, as measured by a manometer, exerted by t h e current of moving gas on two tubes, one of which was straight, t h e other being bent a t a right angle, and turned so t h a t t h e current of gas would blow into it. I n using this anemometer. i t was t o be inserted into t h e air current t o t h e extent of about one-sixth of the diameter of t h e flue. The velocity a t this point was assumed t o be nearly equal to t h e average, and t h e velocity was based on a reading taken a t this one point. Lunge admits t h a t the accuracy of t h e assumption is doubtful, and adds: "There are no means a t present1 known of measuring t h e absolute quantities passing through a flue of any considerable sectional area with any degree of accuracy." Since 1903 numerous investigators have published accounts of t h e results of their work on pitot tubes. Different forms of pitot tubes have been designed, each designer claiming for his form, perhaps, superior accuracy. With so many different forms of tubes, none acceptable as a standard, engineers were as badly off as if there were no pitot tubes a t all, and, in fact, all forms of pitot tubes were more or less distrusted. I n September of last year, t h e results of an exhaustive series of comparative tests of t h e different forms of pitot tubes were published by W. C. Rowse.2 Thanks t o t h e painstaking work of this investigator, i t is now possible t o separate the wheat from the chaff, and a form of pitot tube may now be selected with some confidence. Those interested in t h e velocities of gases cannot do better t h a n read the whole of t h e paper by Rowse, which, with diagrams, tables, etc., covers about fifty pages. With the consent of t h e author, t o render his paper of still greater value, two errors in t h e statement of formulas which inadvertently crept into his work are here pointed out. On page 1343, paragraph 46 (lz) reads as follows: " It appears t h a t an approximate relation exists between the mean velocity head of a gas flowing through the pipe and t h e velocity head found by placing the t u b e a t the center of the pipe. For a 12-in. galvanized iron pipe results within 2 per cent may be expected from using t h e formula ~ ~ ~~ where v = d ( 2 g ) (0.80) hc 2) = velocity in feet per second. g = 32.2 ft. per second per second. h, = velocity head in in. of gasolene a t the center of the This is all correct except t h e value given t o hc, h ' = velocity head in feet of gas flowing at the center of the Again, on page 1 3 7 2 (paragraph 76) a formula is pipe obtained in a correct manner " which should read: pipe, obtained in a correct manner. given which reads: where it = velocity head in feet of air. s = sp. gr. gasolene. p = weight of water in pounds per cu. in. taken from H = velocity head in in. of gasolene as given in columns 11903. 2 J . A m . SOC. Mech. Eng., Sept., 1913.