A Piezometer Ring CHESTER P. BAKER AND ALBERT J. KOMICH Chemical Engineering Laboratory, Northeastern University, Boston, Mass.
T
HE static pressure of a TO M a N o M E r E u
moving liquid in a pipe line may be measured by a manometer attached t o a small opening in the pipe wall, the plane of the opening being parallel to the direction of flow. Such a connection, however, may give faulty readings owing to the disturbance of the flow by unremoved burrs a t the base of the drilled hole or by the protrusion of the tap beyond the inner wall surface. The readi n g s m a y n o t be simply a measure of the static head, but may include a fraction of the velocity head should t h e stream be diverted up the tap by a sharp downstream edge of the drilled hole. To a v o i d t h e s e p o s s i b l e errors and to ensure greater precision where small static pressure differences are concerned, the form of piezometer ring shown in Figure 1 was constructed in the authors' laboratory and found to be very satisfactory.
OMETER TAP
/ N MANIF OLD
FIGURE 1. PIEZOMETER RING
The improvised piezometer consists of two reducing couplings, one nipple, and a short piece of pipe threaded on one end for a It is constructed as follows: ta $he upstream section of pipe is threaded to receive one of the reducing couplings, into which is screwed a tapped nipple as shown in Figure 1. The downstream pipe is threaded and the second coupling is put on. Now the two sections of pipe are joined by screwing the second coupling onto the remaining end of the nipple. The threaded lengths are gaged so that the opening between the upstream and downstream lengths of pipe is not more than 0.0625 inch. The split between the two sections
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is the most important part of the ring, as it is the point at which the ressure is measured. To avoid the effect of velocity head on tEe manometer, the tap in the ni ple must be upstream from the static split. The inner edges or the split must be rounded to reduce the friction loss, t o encourage flow through the pipe, and to prevent divergence of the flow into the manifold. The improvised piezometer ring described is constructed from fittings which may be purchased from any dealer in pipe fitting supplies and can be put together with the minimum of shop equipment. It has been used successfully for the determination of the friction loss of pipes and pipe fittings. RECEIVED August 26, 1937.
Determination of Silicon in Aluminum-Correspondence SIR: Churchill, Bridges, and Lee published in the May 15, 1937, number of INDUSTRIAL AND ENGINEERING CHEMISTRY (4) a paper on the above subject containing a number of results which were obtained during an official examination by the A. S. T. IM. of my methods published in the Analyst (1, 2, 3). Some published comments on these results seem t o be necessary to clear up certain difficulties and misunderstandings which, as it appears from this paper from the Aluminum Company of America Laboratories, seem still t o exist in America. In my first paper (I), I pointed out that the tri-acid process recommended by the A. 5. T. M. tended to give low results due to the loss of silicon as silicon hydride. In my second paper (g), I gave the actual results for the determination of sdicon hydride lost f r m various classes of metal during solution in different acids and in soda. In my third paper (3), I gave full details of an accurate method for the determination of graphitic silicon in the residue from acid attack. The main point brought out by my results was that with
aluminum containing as principal impurities iron and silicon only, and in the chill cast condition-i. e., rapidly cooled-some of the silicon was in solid solution in the aluminum unless the iron content of the metal was abnormally high. When the metal was dissolved in mixed acids a part of this silicon in solid solution in the aluminum went off in the form of silicon hydride and was lost from the analysis. To bring out this important error clearly it is advisable t o take metal with high silicon (say 1.5 per cent) and low iron (say 0.10 per cent) and anneal it at about 570" C. for 24 hours and quench in cold water. Also, since such metal has a tendency to aging and this is accelerated by any heating up during the turning or milling of the sample for analysis, special precautions must be taken t o keep the metal cool and analyze it immediately after quenching.
Unfortunately in the A. 8. T. M. investigation they did not appreciate these rather complicated metallurgical points and 533
