66 HOSACK-STEAM BOILERS. of "Medical Essays;" together with a System of Practical Nosology," the first edition of which appeared in 1819, and a second in 1821. His other writings are a discourse on Horticulture, one on Temperance, biographical notices of Dr. Rush and Dr. Wistar, and an elaborate memoir of De Witt Clinton. - Dr. Hosack was a Fellow of the Linnæan Society of London, of the Royal Society of London and of the Royal Society of Edinburgh, and also a member of the American Philosophical Society. He died of an attack of apoplexy, on the 23d of December 1835, in the 67th year of his age. 651 Warren county, N. C., on the 29th of June 1837, in his 79th year. SMITHSONIAN INSTITUTION. Congress, towards the close of its late session, passed an act, which was approved by President Polk on the 10th of August, establishing this institution. Its provisions, however, go very little farther than the appointment of a board of regents to conduct the business of the institution at the city of Washington. The board is to be composed "of the vice-president of the United States, the chief justice of the United States, and the mayor of the city of Washington, during the time for which they shall hold their respective offices; three members of the Senate, and three members of the House of Representatives; together with six other persons, other than members of congress, two of whom shall be members of the National Institute in the city of Washington, and resident in the said city; and the other four thereof shall be inhabitants of states, and no two of them from the same state." The board of regents are authorized to select a proper site for the institution; and as soon as they "shall have selected the said site, they shall cause to be erected a suitable building, of plain and durable materials and structure, without unnecessary ornament, and of sufficient size, and with suitable rooms or halls for the reception and arrangement, upon a liberal scale, of objects of natural history, including a geological and mineralogical cabinet; also a chemical laboratory, a library, a gallery of art, and the necessary lecture rooms. An important provision of the act is, that all expenditures and appropriations, to be made from time to time to the purposes of the institution, shall be exclusively from the accruing interest, and not from the principal of the Smithsonian fund. MACON (Nathaniel) was born in North Carolina, in the year 1758, and was educated at Princeton, New Jersey. While at college in 1776, he performed a short tour of duty against the British who had invaded that part of the country; and on his return home in the spring of 1780, he joined the militia troops of his native state, and continued with them till the provisional articles of peace were signed, in the autumn of 1782. While yet in the army, and when scarcely 24 years of age, he was elected by his fellow-citizens a member of the Legislature, without his solicitation or even knowledge. After serving 8 years in this capacity, he was chosen a representative in Congress, and took his seat as such at the 1st session of the 2d Congress, in 1791. He occupied it uninterruptedly till the winter of 1816, when he was transferred to the United States Senate, of which body he continued a member down to the month of November 1828; at which time his advanced age and infirmities induced him to resign his seat. During his congressional career, Mr. Macon was elected in 1801 speaker of the House of Representatives, at the 1st session of the 7th Congress; and he continued to preside over its deliberations STEAM BOILERS (Explosion of). The till the 10th Congress. The duties of the constantly increasing use of steam as a chair were discharged by him with ability, moving power in the arts, and the many and with an impartiality acknowledged by painful accidents connected with the emhis political adversaries. He was several ployment of this agent, render important times chosen president pro tem. of the the general diffusion of all knowledge reSenate; and the office of postmaster-gene- lative to the causes of the bursting of ral was twice offered to him and declined. steam boilers. The most valuable set of In 1835, his fellow-citizens called him from experiments ever instituted on this subject, his retirement, by electing him a member was made by a committee of the Franklin of the convention for revising the consti- Institute of Philadelphia, at the expense tution of N. Carolina; of which body, too, of the secretary of the treasury of the he was chosen to be the president by a United States, i. e. the expense of the apunanimous vote; and the last public duty paratus was defrayed by the general gowhich he performed was that of an elec- vernment. The services of the committee tor of president and vice-president of the were gratuitous, although they were renUnited States, in 1836.The death of dered at the expense of much time and laMr. Macon occurred at his residence in bour; and the chairman, Dr. A. D. Bache, now of the coast survey, devoted the greater part of all his leisure hours during four years to the investigation. Previous to commencing the experiments, the committee addressed a circular to every engineer known to them as connected with the practical application of steam, and who had any personal knowledge of the explosion of a boiler. The answers to these circulars, though containing many crude hypotheses, furnished a valuable collection of facts and suggestions, which served to guide the researches of the committee. The causes of explosion were considered under the following heads: I. Explosion from gradually increasing pressure of steam.—It was asserted in several of the answers to the circulars, that a mere rupture, and not an explosion, is produced in boilers, particularly of copper, by gradually increasing the quantity of steam. The committee, however, proved by the most conclusive experiments, that violent explosions are produced in boilers, both of copper and iron, by a gradual increase of the tension of the steam.-Explosion from this cause can only take place on account of some defect in the action of the safety apparatus; and the circumstances which may lead to this are(1) designedly loading the safety valve, to increase the power of the engine-(2) the adhesion of the valve, from rust or some other cause - (3) the obstruction of the free motion of the lever, such as the falling of a piece of timber across it, &c.(4) also the form of the valve may have some influence. II. Explosion from the presence of unduly heated metal within the boiler.-The researches of the committee show that this is a frequent cause of explosion, and that the effect is neither due, as many suppose, to the production of gas from the decomposition of the water, nor to the flashing of the liquid into vapour when thrown into surcharged steam, but to the sudden generation of a great quantity of steam when the water comes in contact with the heated metal. The increase of pressure in this case is so rapid that the sides of the boiler give way before the resistance, and the inertia of the safety-valve can be overcome. The circumstances which attend explosions from this cause are as follows: (1) A deficiency of water, which exposes a portion of the naked metal to the fire. This may be produced by a defective action of the feed-pump, or by blowing off steam while the engine is at rest; when the pump is again set in motion, the water is thrown on the heated metal; or the mo tion of the vessel may "swash" the water over the heated surface; and also when a head of steam is allowed to blow off, the water foams up, and in this way it may come in contact with the heated metal.— (2) Metal may become unduly heated by a deposit of earthy matter, which incrusts with a bad conductor the bottom of the boiler. When a crack is produced in this, the water is let down on the heated surface. The whole crust may thus be blown off, and the bottom suddenly exposed.— (3) From the careening of the vessel the water may be thrown on the lower side of the boiler, leaving the opposite side uncovered; when the vessel returns to its horizontal position, the water is thrown on the heated metal. Explosion is most liable on this account in vessels provided with a number of parallel boilers connected together. When the boat stops at a wharf to land passengers, the weight is thrown on one side; and at the moment of starting, the return of the water gives rise to the explosion. It should be observed under this head that the tenacity of the metal is diminished by increase of temperature; and hence the boiler, when highly heated in any part, is less able to withstand a high pressure. III. Explosion from defective construction of the boiler.-The cylindrical form is the strongest; and with the same capacity and thickness of metal, the less the diameter the greater is the pressure it will sustain. The committee condemn the use of connected parallel boilers (unless divided into pairs) on account of their liability to expose metal uncovered with water to the heat. They consider also all boilers furnished with flues less safe than those without them. The flue passing through from end to end is the least objec tionable, while the L flue, the vertical part of which passes out of the upper side of the boiler through the steam, and not surrounded with water, is considered the most dangerous. All irregularities in the form of the boiler are attended with a weakening effect; and hence tubes and other appendages projecting into the interior of the boiler to increase the fire surface are objectionable. The material should be wrought-iron or copper. The former is however more liable to be corroded with salt water, and hence the latter should be preferred in situations exposed to this action. IV. Collapse of boilers. Accidents properly referable to this cause are of rare occurrence; they sometimes happen in large low-pressure boilers, when the pres STEAM BOILERS. sure of the steam within is less than that of the atmosphere without.-In one case, the partial vacuum produced in the smoke flue of a boiler, by the explosion of a quantity of coal gas, was attended with a collapse of the flue: this fact should suggest care in avoiding the explosion of gases from the combustibles under the bottom of the boiler. The collapse of an interior flue is sometimes produced by the gradual increase of the pressure of the steam. This however may be considered as an instance of internal bursting. 653 in case of accident. The custom of employing incompetent engineers, because they can be procured at a low price, cannot be too strongly reprobated. The committee recommends the use of fusible metal, contained in a tube closed at the bottom, and inserted into the interior of the boiler, so as to be surrounded with steam. When the temperature increases to a given degree, the metal melts in the tube, and thus unsolders the end of a rod; which, by means of a falling weight, may ring a bell, or throw a load from the V. Explosion from carelessness, igno- safety-valve. The suggestion of this merance, &c.-The management of the thod of employing the fusible metal is steam-engine cannot safely be entrusted separately due to Dr. A. D. Bache, and to a person who has not at least a general Mr. Evans of Pittsburgh. The latter has knowledge of the nature of the power with taken out a patent for a safety apparatus which he is entrusted, or who does not on this plan, which is the best contrivance possess the requisite feeling of moral re- for the purpose we have ever seen desponsibility to exercise his knowledge with scribed. Nothing, however, but caution prudence. The engineer should in all and attention, with requisite knowledge, cases perform his duties under an assur-will prevent accidents from steam exploance of the infliction of a severe penalty sion. |