Arkansas true Democrat., 1858-03-30

injured or deterlorateu III sreGSIn utii us teui- perafure approaches six hundred degrees."- According to the Franklin Institute, "when iron is heated above the temperature of 392 de- grees it imbibes the oxygen of the atmosphere. , So authorities differ If iron at 3S2 degrees i'm bibes oxygen, it must thereby be injured. But the-supervisors say it will not be injured till its temperature approaches 600 degrees!
 If high pressure boiler will stand hydros- tatic test of little more than one-thlrd the pressure it is designed to bear when in use, 1t is duly approved by the inspectors and its use Accused accordingly. For example: if boiler
 intended to carry steam pressure of l60 pounds will stand a hydrostatic pressure of 221 pounds, it is regarded as coming within the requirements of the law. But the steam pressure must ex- ceed the pressure limited by law in 230 degrees before the tin plugs will begin to operate.
 "It is easily perceived that this will make the tin plug a safe guard against explosions from low water as the danger of such explosions arises from overheating of that part of the boiler which is left exposed to the action of the hre' in conseQuence of the water being permitted to fall too low to protect the iron from excessive heat.''
 That there is great danger from low water combined with excessive heat, is point beyond dispute; but we cannot see that an adequate re- mcdv is to be found in blocks or rvets of pure tin. IL is quite possible for us to conceive that the water may fall dangerously low, before either the steam or the iron shall have attained the temperature of 442 degrees.
 "These plugs may be put in the boiler at diff ferent places if neeessary-that Is ln the most exposed parts of the fues."
 Well, we'll It Is an awful thing to be scald- cd to death; and hardly less awful for man to loose lis eye sight, or be blistered all over by hot steam or boiling water. If tin plugs can be of any use in preventing such dire calamities, in the name of suffering humanity let us have them. But, in the name of common sense, let us not trust to them alone.
 The reader must listen to the residue of the remarks of the supervising inspectors
 "The great advantage claimed for the tin plugs over the alloy is, that the tin being sim pe and not a compound metal, like the alloys, it can be used in the shape of a simple plug or ri.et, made to fll a hole in the boiler, which Is prepared for the purpose of receiving 1t, by which it will be exposed to the direct action of the fire in the sane manner aS the boiler itself, without the risk of is changing its nature in consequence of the heat and pressure to which 1t would he sUbiected; whereas the alloys, in order to avoid these effects, must be enclosed in an apparatus made suitable for the purpose, and operated by some mechanical device in order to relieve a valve which will let steam escape at the melting of the alloy, all of which as ex- pareuce has proved, aud IS clearly set forth n the communications referred to this committee, is attended with difficulty, uncertainty and dan ger"
 We fully admit that tin plug is more sim pe apparatus than all Evans safety guard But, after all the latter, which consists of metallic cup, metallic tube metallic spindle and a metallic chain, is not a very complicated piece of machinery. The experiences set forth in the communications on which tLe supervisors depend so much, we have as we conceive, treat ed of sufficiently already.
 "The tin plug, 1t is true, guards against dan gers from one source only-that of low water in the boilers; whereas it is claimed that the al lovs will guard against both deficiency of water and over pressure of steam; but inasmuch as the alloys have from some cause or other, in seve- ral instances failed to operate when the condi- tons of explosion were beyond all doubt in eX- istence, from either too low water or too high steam, it has been thought proper to have more sure guaranty against only one of these causes, than run the risk of failing in both, particu- larly when that one Is very well known to be the source of probably nineteen out of every one of the explosions that occur. Besides 1t will not be a difficult matter to devise other means whereby a more perfect security can be obtained against the violation of the law by carrying all over pressure of steam."
 Here tn, supervisors state that "the alloys have, from some cause or other, in several in- stances, failed 10 operate;" but they do hot say under what circumstances. We have now be- fore us letter from gentleman, dated Pitts burg Penn, August F, 1857, which throws some light OH this subject. The writer says:
 Within few days have discovered plan for preventing the action of the guards, which appears to be of quite general adoption in this section. On visiting all the boats now at our wharf, found no less than nine boats with the chains so tied to the spindles, and then hooked so short that it was impossible for the nstru- ment to operate. think the enforcing of the penalty named n section eleven of the steam boat law would have wholesome effect. These facts are strong evidences of the efficiency of the guards, as it requires special care to prevent their operation"
 If engineers will be so reckless of consequent ces as to tamper with the safety guard, and ii inspectors will be so negectful of duty as to conRive at such doings, the fault ought to be aid where it lies, and not on the fusibe alloys.
 In conclusion, the supervisors say:
 i've would further state that from the best information we can obtain, these views in re- gard to the use of alloys and tin plugs are fully sustained by the present English and French practice"
 Our latest information is that the alloys are still in high favor in France. But supposing the information of the supervisors to be correct, have the English or the French made fair trial of the alloys on Mir. Evans plan-so as to ex- clude the pressure of steam, and operate on a safety valve of sufficient dimensions? If they have not, their experience is nothing to the point We can easily believe that they are ready to abandon the use of fusible alloys in plugs and open tubes. In this they form ought to have been abandoned long ago.
 Besides this, it ought to be borne in mind that the English and French use generally low pres sure boilers, while we, on the midland waters of the United States, use chiefly high pressure boilers, and it is only tS high pressure boilers that our law requires the fusible alloys to be applied.
 $. In addition to this it is proper to observe that the English law requires that each boiler shali have tico safety valves one of which shall be placed beyond the control of the engineer. They thus have precaution against danger which we have not.
 We have given in full the reasons urged by the supervising inspectors in favor of a chance