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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
lent of this amount in time in a short while. Since in a publication as large as t h e proposed index t h e cost item for paper, presswork, binding, etc., is quite large i t is probable t h a t under t h e existing circumstances only a few copies over a n d above t h e number subscribed for can be published. There will no doubt be a time when these indexes will command a considerable premium. T h e American Chemical Society is the largest chemical society in t h e world. I t has undertaken much in publishing Chemical Abstracts.
Vol. 7, No.
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I t is conceded t h a t this undertaking has been worth while a n d successful t h u s far. A collective index is necessary t o its continued success. We must do a t least as well as t h e smaller foreign societies. America's place in future chemical development is perhaps hard t o forecast with precision. It may be expected to be high. We have t h e resources, a n d chemical use of t h e m is just beginning. We must properly continue t h e important work we have undertaken. E. J. CRAKE
ORIGINAL PAPERS AN INVESTIGATION OF FUSIBLE TIN BOILER PLUGS B y G. K. BURGESSA N D P. D. MERICA
Received June 14, 1915
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B
T h e fusible boiler plug in its usual form consists of a brass or bronze casing with external pipe t h r e a d , filled from end t o e n d with a fusible metal or metal composition, which has a low melting point. These are fitted a t various places into t h e boiler, in such a position t h a t t h e y are about one inch or more above t h e dangerous low water level, with one end on t h e fire a n d one end on t h e water side. As long as t h e water level in t h e boiler is above these plugs, t h e t e m perature of t h e latter remains below t h e melting point of t h e filling ( a t I jo pounds boiler pressure t h e temperature is about 180' C. or 324' F . ) , b u t if t h e water falls much below t h e level of t h e plug, opport u n i t y is given for a local overheating in t h e vicinity of t h e plug. T h e filling of t h e plug t h e n melts a n d is blown out. T h e fusible plug has been required t o be installed in all steam vessels of t h e American Merchant Marine since 18j2, a n d is now required in all boilers except pipe, flash, or coil boilers on vessels subject t o inspection b y t h e Steamboat-Inspection Service, Department of Commerce. This inspection includes approximately I 1,850 boilers requiring installation of boiler plugs. Fusible plugs are also used in many b u t not all factory a n d locomotive boilers in this country a n d abroad. T h e y are not generally used in marine boilers abroad, nor are t h e y used in t h e United States Naval service, t h e practice there not favoring t h e installation of safety devices of a n y sort, fusible plugs or otherwise, as it is considered t h a t their presence fosters negligence. Tin seems t o be t h e metal used a t present almost exclusively as t h e fusible constituent of such plugs, a n d is required b y t h e above specifications. I t would seem t o be in this respect a desirable metal, having a low melting point, being only slightly corrodible, a n d easily obtained pure. Its desirability in this respect is nevertheless t o some extent called in question by t h e results of t h e investigational survey of fusible t i n boiler plugs, which was made a t this Bureau, from J u n e , 1914,t o March, 1915. On M a y 1 1 , 1914,a boiler of t h e Steamship J e f l e r s o n exploded, causing t h e loss of life of several persons. Investigation showed this explosion t o have been due
t o low water and consequent overheating of t h e boiler plates. This should have been indicated by t h e fusion of t h e filling of t h e Banca t i n plug in t h a t region, which plug, however, was found t o be unmelted a n d apparently, or a t least superficially sound. This plug was sent t o t h e Bureau of Standards for investigation. At this Bureau it was sawed open longitudinally a n d was found t o contain traces only of t h e original tin, embedded in a dirty, greenish matrix. A photograph of this central longitudinal section is shown in Fig. I, i n which t h e light regions represent t h e remaining tin. The matrix was found t o be largely t i n oxide, SnOs, which upon test showed a melting point above 1600' C. (about 2900' F.). This oxide was distributed in such a form a n d q u a n t i t y t h a t i t held t h e pressure of t h e boiler, a n d would not h a v e melted until t h e bronze of t h e casing a n d even t h e steel of t h e boiler had melted! When reliance is placed upon such a plug t o give warning of dangerous boiler conditions it is t o be looked upon a s a n actual source of danger instead of s a j e t y . T h e question arose t h e n : T o what is t h e presence of t i n oxide t o be ascribed? Was it there originally, has i t been formed b y corrosion, a n d if so, is t h e cause for its comparatively rare occurrence in such plugs t o be sought wholly in t h e different operating conditions of t h e boilers, or is a fault in t h e method of manufacture of these plugs a t least partially responsible? A search in t h e literature failed t o reveal a n y reference t o failures of fusible t i n plugs of this s o r t , except vague statements t h a t t h e y were not entirely reliable, due t o t h e formation of boiler scale on t h e inside a n d soot on t h e outside a n d a statement t h a t t h e filling was likely t o change its melting point during service. N o d a t a could be found concerning t h e oxidation of t i n a t higher temperatures. A request was t h e n made t o t h e Steamboat-Inspection Service t h a t more plugs be sent in t o t h e Bureau for t e s t , both new ones, a n d also those which had been removed by t h e inspectors, in order t h a t b y a survey of these plugs information might be obtained bearing on t h e points raised above. I n answer t o t h e request, about ~ o j oplugs were received of which about I O O had been in service'varying from 4 t o 1 2 months. These plugs represented t h e products of about 1 0 5 fir ms . E X A M I N A T I O X AND IXVESTIGATION O F PLUGS
T h e plugs were first examined t o ascertain whether
OCt., 191s
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