ANALYTICAL EDITION
July, 1946
The pyrophthalone compounds are yellow dyes, the propertiei of which have been described by Hewitt (1). This formation of pyrophthalones may be traced to the presence of 4picoline or 2,6-lutidine, or both; and it has been recognized that a methyl group in position 2, 4, or 6 is necessary for condensation with carbonyl groups. Two hydrogen atoms from thepicoline and one oxygen atom from the phthalic anhydride are released to form water. However, the methyl group in the 3 position is entirely unreactive and therefore no color develops. The p-picoline may be considered absolutely free of its isomers and homologs when there is no appearance of color following this treatment.
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Pure @-picoline is extremely liydroscopic and precautions should be taken to keep it absolutely dry. Slight traces of any of the usual impurities in a sample of 8picoline will be detected by the appearance of yellow color on refluxing with phthalic anhydride and acetic anhydride. Therefore, if no color develops, the picoline may be considered free of these impurities. The sensitivity of the method and long color stability allow for color comparison as the purification procedure is repeated; and it is possible that a quantitative colorimetric method may be developed for particular conditions, such as the control of manufacture or use where the same impurities are commonly present in about the same relative amounts. This method serves a tl%-ofoldpurpose-purification of @-picoline and qualitative analysis of @-picolinefor its common impurities. LITERATURE CITED
(1) Hewitt, “Synthetic Coloring Matters”, London, Longmans, Green and Co., 1922. (2) Itiethof, George, L-. 9. Patent, application pending.
Modified Gate Valve for Control of Water Flow G. ROSS ROBERTSON, University of California, Los Angeles, Calif.
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ABORATORY workers have long deplored the fact that a water faucet, adjusted t o low rate of Aom, often shuts off the stream spontaneously. This treacherous habit unfortunately is a special failing of the “compression” valve, a device conceded
In the standard commercial gate valve, A , a brass gate normally rises and falls across the water stream with rotation of the left-hand-threaded shaft and wheel handle. As shown in the separate vien. of the gate, E , a narrow slot is cut in the extreme edge of the gate. This slot permits the passage of a small but very definite and constant stream-for example, a t adjustment B. The stream is precisely adjustable between values fully double that a t B down to wsition D. where the stream is reduced practically t o zero flom-. :It the same time it is possible to open the gate to full flow as needed. The modified gate valve thus has a much wider range of usefulness than a needle valve rrhich might serve a t position GT‘ to provide a small stream. Since it is unnecessary and undesirable t o have a narroIT slot on bot,h sides of the gate, the lower side (as of gate in position E ) is cleared for unrestricted flow with a iTide slot, whose operating position is seen at’ F , which merely shows the opposite threaded end of valve A . I n steady service of one kind from day to dayfor example, to a reflux condenser-little or no adjustment of GV is required, and thus undue wear is obviated. MECHANICAL SPECIFICATIONS. X standard plumbers’ brass gate valve, usually 3 / ~ or inch (“iron-pipe-size”) is selected, choice being based on maximum width of the annular ground contact surface of the gate. Such maximum width permits maximum length of slot n i t h limit shoxn in D. The slot is cut with a fine jewelers’ saw; a blade 0.31 mm. in width was found to be satisfactory. The resulting slot is of suitable width for use with n-ater pressure of 60 pounds per square inch, or approximately 4 kg. per sq. cm. It should be noted that the opposite and supposedly identical contact faces of a gate are often of varying annular width, or overlap. The wider, with the greater overlap, is selected for the narrow slot, B, and the narrower, also cut TT-ith the saw, for 8’.
E
B
to be the most satisfactory faucet yet developed. I n the new arrangement shown in the figure, the regular compression valve, CV, with washer, is retained for leakproof on-and-off service. Adjustment to low rate of flow is delegated to a second device, the modified gate valve, GT‘.
F
Since this mechanical alteration requires disassembling of the gate valve, inexperienced workers are warned that nut N must not be opened while the valve is cloqed, lest the interior mechanism be sprung and the valve ruined. Instead, the gate is first screwed out about half way. The valve is now fastened securely in a vise, with vise jaws pressing upon the two threaded mouths of the device. Nut N may then be started without mechanical damage, and the parts separated hy finger contact only.
