motion is not effected with the velocity essential to an efficient process of expansive action. Other processes have been tried för working steam-engines expansively, besides those already noticed; amongst them may be noticed the equilibrium valve, worked by double cams from the crank shaft. This method is generally used and adapted to the marine and old engines; but its application is seldom of much value, unless the engines and boilers are capable of bearing a pressure of 15 lbs. to 20 lbs. on the square inch.

Another fault to which this description of valves is subject is, their distance from the steam-ports into the cylinder, and the large quantity of steam which occupies the space between the cut-off valve and the working cylinder of the engine.

To remedy these defects, and to apply a better system of expansion to the common condensing engines, the following apparatus and mode of working the valves was introduced.

In giving a description of this effective and simple apparatus, it is but fair to state that the first idea of this invention was suggested by Robert Brownhill, at first imperfectly constructed, but since greatly modified and perfected by the author of the present paper.

In the construction of a steam engine, two important considerations present themselves, the attainment of a maximum of force, and the minimum in the consumption of fuel. To acquire the first, it is requisite to form such an arrangement of the working parts as to obtain the closest approximation to a perfect vacuum under and above the piston, and the other is accomplished by having as small an expenditure of steam as possible. These desiderata are, to a great degree, attained by the principle upon which these valves are constructed, and the way in which they are worked. Each of the steam chests contains two double-beat valves, one for the admission of the steam to the cylin der, and the other for its escape into the condenser; also the shut-off valve and the throttle valve; and these valves constitute the whole of the openings by which the steam is admitted and returned from the cylinder. All the four valves are of the same area and dimensions; but the steam valves are not lifted up so high as the exhaust valves, for the reasons which are afterwards given. The double-beat valves of this construction have certain propor tionate areas, the upper portion being larger than the bottom, in the ratio of 1'158 to 1.000. The object of this enlargement of the upper part of the valve is to give à pres ponderance to the pressure of the steam ori

the top side, in order to overcome the pressure of the packing in the stuffing-box which embraces the spindle, and to assist the gravitating force of the valve in its descent when liberated from the cams.

The mode of working the valves is by shafts and wheels, which derive their motion from the crank shaft, and revolve at the same speed. A vertical spindle, tipon which two circular discs, P P, are fixed, passes through the steam chests, and by its rotary motion the cams which are fixed upon these discs raise the valves as they pass under rollers, which are connected to the valve spindles by cross heads, M M. By these means the valves are raised and retained open or shut for any definite period. The rollers are steadied by the cross heads sliding upon the vertical guide-rods, at their outer ends, and sliding at their inner ends in vertical grooves in a centre boss, which is supported by the guide-arms.

To work this engine economically, much depends upon the pressure of the steam and the amount of expansion given to the valves. The usual practice is to work with steam, at 15 lbs. on the square inch, and cut off at one half the stroke, and expand the other half; but in other cases, when the engines and boilers are calculated to bear a high pressure of steam, (say from 30 to 40 lbs. on the inch,) the cams are formed so as to cut off the steam at one-third or one-fourth of the stroke. There are generally three and sometimes four cams upon each of the discs, so as to cut off the steam at one-half, one-third, or one-fourth, or at any other point corresponding with the force of the steam and the load respectively.

To obtain this range of expansion, the rollers which work the steam valves are movable, by brass strips which slide in the grooves in the cross heads, 60 as to bring the rollers over any one of the cams that may be required; and there are fixed pointers which show, by a graduated scale on each brass slide, the exact point of the cylinder at which the steami is cut off, and by these means the extent of expansion is regulated, and brought under the eye of the engineer.

It has already been stated that the steam valves are not lifted so high as the exhaust valves, and the reason of this is, that as the exhaust valves are hot variable in theit action, and always require full openings into the condenser, it is desirable to retain them open throughout the whole length of the stroke. This process is effected with à greater degree of certainty than by any other description of valve. The exhaust valves are raised suddenly by the short inclined planes of the cants, and having

The returns received enumerate 233 explo sions of steam-boat boilers, from which accidents the number killed (as given in 164 cases) is 1805; making an average of 11 for each accident. If the 69 cases in which the number killed is not stated average the satte; the total loss of life, in the 233 cases, would amount to 2563.

The number wounded, in 111 cases, is 1015-an average of 9. The same calculation as in the former case would give as the total number wounded, 2097; making the whole number of sufferers 4660.

The amount of pecuniary loss sustained in 75 cases is 997,650 dollars-giving an average loss of 13,302 dollars by each ex plosion; which, applied to the whole num. ber of cases, would make the entire loss 3,099,366 dollars.

Of the explosions enumerated, 202, or 867 per cent., occurred on the southern and western waters; 146, or 626 per cent., on the Mississippi fiver and its tributaries; 90, or 386 per cent., on the Mississippi alone;

40, of 172 per cent. on the Ohio. The number of explosions for each locality is given in detail, in the Appendix [E.]

From 1830 to the present time the number of explosions given is 198; making an average of 10 each year, with 110 as the average annual loss of life, and 90 the an nual average of wounded; the total number of sufferers, annually, being 200; and the annual pecuniary loss 133,020 dollars.

The steam boat tonnage of the westerfi rivers in 1846, was 249,055, and the whole value of the commerce of these boats 62,206,719 fix-dollars. The probable extent in miles of the steam navigation of the western waters, as estimated by Colonel Long, of the topographical engineers, is 16,674. The whole number of steam vessels built in the

There is something in the appalling nature of steam-boiler explosions which strikes public attention, and has given rise to an impression that steam-boats and railroads are more dangerous modes of convey. afice than any others. It is to be regretted that no direct means of making a compari son through a series of years, between the losses by ordinary navigation and those by steam navigation are in the possession of the office:

To make a comparison which should be perfectly fair, it would be necessary to take an equal number of steamers and other vessels having the same route, and exposed in common to the same sources of danger, except those arising from the employment of steam as the motive power. It would be very difficult to obtain the means of doing this. But a general and somewhat loose comparison can be made, which may serve to correct a false impression which undeni ably exists with regard to the comparative safety of the two modes of travel. It appears from a statement contained in a memorial addressed to Congress on this sub ject, that in the year 1839 the number of American vessels lost by ordinary navigation was 1059, and that in the month of December alone of that year, 181 vessels, atid 179 lives were destroyed. Thus the number of lives lost in that month is nearly double the average annual loss of life by steath-boat ex plosions, as deduced from the foregoing cal culations. A comparison of the number of vessels exposed would not give a fair estimate of the relative danger of the two modes of transportation, because the number of individuals exposed to the dangers from steam transportation is vastly greater in proportion to the number of vessels than those exposed in ordinary navigation.

In speaking thus favourably of the com parative safety of steam navigation, it is not intended to assert that steam has not added, in each individual case, a new element of danger to the means of transportation where it is employed. But in endeavouring to esti mate the absolute risk in each kind of navigation, we must take into the account every source of danger to which each is subject, and so doing, we find the risk from ordinary navigation to exceed that from havigation by steam. In the case of the former, disasters frequently occur in a distant quarter, in the

* Rep. Sec. Treas. Dec. 1847. Sen. Dot. No. 5, 30th Cong., 1st Sess., p. 396.

+ Sefi. Doc. 309, 1st session; 26th Congress.

presence of comparatively few witnesses, and many of them are never noticed by the press. They are regarded as matters of course, the results of natural causes, over which man has no control. In the latter, on the contrary, every circumstance is present which would tend to exaggerate the impression upon the public mind. It is merely for the purpose of removing an injurious misconception that the comparison just given, which does not pretend to accuracy, has been made.

For the five years ending with 1828, the ratio of explosions to the number of exposures on steam-boat routes from New York city, was 1 to 126,211. In the next five years, ending with 1833, the ratio was reduced so as to show 1 to 151,931; and in the next five years it fell to 1 to 1,985,787.*

The result of a similar calculation with reference to western navigation is less favourable. In the memorial of a "Committee on Abuses of Steam Navigation at Cincinnati," laid before Congress at its last session, the number of lives annually exposed to the dangers of steam navigation is estimated at 8,185,000. Taking the average annual loss of life on these waters at 70,† we find its ratio to the whole number of lives exposed, to be 1 to 102,642, and the ratio of explosions to the number of exposures to be 1 to 560,616.

From these facts, it appears that the dangers of steam navigation on the western waters, though obviously greater than those at the east, still bear a favourable comparison with those of other modes of water conveyance. Yet so much terror has been excited in the public mind by accidents of this kind, that the prevention of them has (and, no doubt, properly) been considered by those nations which have made most use of the powerful and useful, though dangerous agency of steam, as calling for special legislative interference. As early as 1817, a Committee of the British Parliament was charged with the investigation of the causes of explosions, and much valuable information was elicited by the examination of engineers and others, which they instituted. That Committee felt and acknowledged the inexpediency of "legislative interference with the management of private concerns or property, further than the public safety should demand;" but they urged "that a consideration of what is due to public safety has on several occasions established the

* Redfield's Replies to British Commissioners, Sen. Doc. 309, 1st sessions, 26th Congress. + Calculated by the per centage.

* British Parliamentary Reports, 1817, vol. iv.

principle that where that safety may be endangered by ignorance, avarice, or inattention, against which individuals are unable, either from the want of knowledge or of the power, to protect themselves, it becomes the duty of Parliament to interfere." This principle, has been acknowledged also by the French Government and by our own. Of the propriety and necessity for legisla tion of some kind there can be no doubt; the only question is, as to what the character of that legislation ought to be. The determination of this question involves the consideration of the causes of these fatal occurrences, and the remedies which have been proposed.

The fact that the steam-engine has come into such general use, and has been placed under the management of men widely differing in their education and judgment, and many of them entirely destitute of scientific knowledge, has given rise to a great variety of hypothesis designed to account for the explosions of steam-boilers. Most of them have been mere crude speculations, without any foundation in fact or in physical analogy. Such are the pretended explanations which refer the explosion to the presence of electricity or the generation of hydrogen gas, and its union in explosive proportion with oxygen within the boiler. Of the former hypothesis, it is only necessary to say, that electricity, if present at all, would reside on the outside of the boiler; and of the latter, that the necessary conditions are not present which would render it probable. In the ordinary condition of a boiler, no hydrogen is produced; and if it were present, it could not procure a sufficient supply of oxygen to combine with it in explosive proportion.*

Another hypothesis accounts for the explosion in this way: the water falling below the fire line in the boiler, the portion of the latter thus exposed becomes excessively heated, and communicates its heat to the

The production of hydrogen was referred to the decomposition of water by the heated metal. The conclusions drawn by the Franklin Institute Committee from their experiments to determine "whether any permanently elastic fluids are produced within a boiler when the metal becomes intensely heated," are, "1. That the gas obtained by injecting water upon the bottom of a boiler which was at a bright red heat, was nitrogen gas with a variable quantity of oxygen; it was, in fact, atmospheric air, deprived by the heated metal of more or less of its oxygen. 2. That this air was derived principally from the current into the boiler when surcharged steam had ceased to be formed, and the boiler was left dry; there will therefore be no such quantity in a working boiler where the air must be supplied from the cold water thrown in. 3. That water in contact with heated iron in a steam boiler, the surface being in its ordinary state, clean, not bright, is not decomposed by heat.”—Frank. Jour., vol. xvii., p. 222.

steam, which thus becomes surcharged with heat. Now steam, when heated separately from the water which generates it, follows the law which regulates the expansion of ordinary gases, i. e., it expands th part of its bulk (or nearly) for every degree of Fahrenheit above the freezing point. The increase of elastic force is, therefore, under these circumstances, very small in proportion to the increase of temperature. But while the steam is thus surcharged, a supply of water is sent into the boiler, the surcharged steam at once becomes converted into saturated steam of high elastic power, and an explosion follows. This hypothesis, although ingenious, and long received as the true explanation of the phenomenon, is found to be contradicted by the results of careful and repeated experiments. The committee of the Franklin Institute,* 66 appointed to examine into the causes of the explosions of the boilers used on board of steam-boats, and to devise the most effectual means of preventing the accidents, or of diminishing the extent of their injurious effects;" to whose valuable labours, which have thrown great light upon this whole subject, frequent reference will be made in this report, made a series of experiments in the prosecution of one point of their inquiries, to "ascertain whether intensely heated and unsaturated steam can, by the projection of water into it, produce highly elastic vapour," and satisfied themselves that in no case was an increase of elasticity produced by injecting water into hot and unsaturated steam, but the reverse; and, in general, that the greater quantity thus introduced, the more considerable was the diminution in the elasticity of the steam.†

A fourth hypothesis has been advanced in a communication to this office, from Mr. N. Sawyer, mechanical engineer of Baltimore, which may perhaps deserve the test of experiment. It supposes the water in a steamboiler to be permanently thrown out of level by the unequal pressure on its surface, resulting from the escape of the steam through the throttle-valve, and at one end, and the consequent diminution of pressure at that point. This alteration of level, of course, exposes a portion of the boiler to become unduly heated, and when the working of the engine is stopped, the restoration of level by gravity brings a quantity of water in contact with the overheated metal, producing highly elastic steam, which, according to the author, may result in an explosion. The existence of the difference of level here supposed, is supported by the testimony of Mr. C. Evans, who remarks,

* Dr. A. D. Bache was the chairman of this committee.

t Journ. Frank. Inst. vol. xvii., p. 19.

in an article on the causes of explosion, that "wherever the steam is taken from to supply the engine, there will be the greatest ebullition, and the water will be higher there than in any other part of the boiler."* The Franklin Committee, in their experiments to ascertain "whether on relieving water heated to or above the boiling point from pressure, any commotion is produced in the fluid," found that, "on making an opening in the boiler, even when the pressure did not exceed two atmospheres, a local foaming commenced at the point of escape, followed soon by a general foaming throughout the boiler, more violent in proportion as the opening was increased. Though the difference of level thus produced could not, it is believed, be sufficient to account for the production of a quantity of steam great enough to result in an explosion, yet the extent to which it would operate could be determined only by experiment.

A hypothesis which has been lately advanced, and to which the attention of Congress has been asked, in a published letter from its author, addressed to the Hon. John Davis, of the Senate, would not have been noticed here but for the latter circumstance This explanation of explosion, so far as it can be gathered from the pamphlet in which it is set forth, attributes the phenomena to the action of liberated caloric, set free by relieving the pressure under which its combination with water is stated to be alone possible. This hypothesis seems to have been suggested by the supposed impossibility of accounting for the phenomena of explosion from the gradually-increased elasticity of steam by heat. That a gradual increase of pressure can produce all the effects of the most violent explosions, has been conclusively proved by the experiments of the committee of the Franklin Institute; in which it was shown that the very effects which, in the pamphlet alluded to, are considered impossible to arise from such a cause, did actually follow the graduallyincreased tension of the steam. § The existence of one sufficient cause, fully supported by the experiments of men so distinguished for scientific ability as were the members of that committee, renders unnecessary a resort to vague hypotheses, unfortified by facts, having no foundation in physical analogy, and, as in the present case, based upon an assumption in contradiction of a well-known physical law. Such hypotheses can only serve to divert the minds of practical men from the true causes

*Pittsburgh Morning Chronicle, March 2, 1848. ↑ Frank. Jour., vol. xvii., p. 8. Pamphlet on "The causes and Effects of Explosions in Steam Engines," &c., by John Wilder New York, 1847.

Rep. on Experiments, p. 68.

of these fatal disasters, and thus still farther to embarrass the question of their proper remedy,

The question of the causes of steam-boiler explosions, if ever solved, is to find its solution in the researches of men of true science, conducted by the order of the Government, and at its expense. The experiments necessary to its full elucidation require too heavy an outlay to be within the reach of the means of private individuals, or even institutions; and the nature of the interests to be protected have made them, by the acknowledgment of all, a proper object of public appropriation. The most valuable contributions to our knowledge of the causes of explosions have been made by the scientific labours of the committee of the Franklin Institute, undertaken at the request and prosecuted at the expense, so far as the apparatus was concerned, of the Treasury Department, in 1831, The ser vices of the committee were gratuitous, although rendered at the expense of much time and labour, and the chairman, Dr. A. D. Bache, the present superintendent of the coast survey, devoted the greater part of his leisure 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 undersigned cannot but believe that the institution of a new series of experiments on the same subject, conducted in the same spirit, and on the same liberal scale as those of the committee alluded to, would serve to confirm the knowledge already acquired, and throw still further light upon this interesting and important inquiry.

The causes of explosion, as laid down by the committee, are:

1. Excessive pressure within a boiler, the pressure being gradually increased.

2. The presence of unduly-heated metal within a boiler.

3. Defects in the construction of a boiler or its appendages.

4. The carelessness or ignorance of those intrusted with the management of the steamengine.+

The causes, so far as they are stated in the returns to this office, may all be included under one or other of these classes, and they have accordingly been so classified in the

*Eneye. Amer., vol. xiv. p. 652.

+ General Report on Explosion, p. 6.

summary found at the end of the Table of explosions. [Appendix C.]

How far these causes are correctly assigned, the undersigned is not able to say, as the means by which they were ascertained are not known to this office. It is desirable that in case of future explosions, provision should be made for obtaining full and accurate information of the nature and causes of the accident. Entire reliance cannot be placed on the testimony of ordinary eyewitnesses, however honest their intentions, and still less confidence can be reposed in that of the engineers and officers of the boat on which the accident occurs, as they are directly interested in showing that it was the result of no dereliction of duty on their part. But, improper influences aside, per. sons unacquainted with the nature and properties of steam and the steam-engine are not competent to form an opinion of any value upon the causes of an explosion. Nor are those who have a merely practical knowledge of these matters in a better situation for this purpose. They have too often preconceived opinions or hypotheses to which they are anxious to make facts agree, and, without intention to deceive, they are apt to seize upon those facts which seem to justify their prejudices, and disregard others of a different tendency. It is to an investigation by scientific men alone,-men who value hypotheses only as they are in accordance with, and serve to account for, facts, and who are ready to abandon them whenever and as often as they are found to conflict with well-ascertained facts,-that we are to look for a satisfactory determination of the causes of these disasters. It might be made the duty of the inspectors of steamboilers, to keep an accurate record of the explosions which occur in their several districts; they might be authorized to procure an examination in every such case by persons having the necessary scientific qualifications, and required to report at stated periods to an appropriate bureau at Washington. The collating and comparing of the information thus furnished would, doubtless, lead to valuable deductions, and have an important bearing upon future legislation with reference to this subject. In a great majority of the cases embraced in the accompanying Table, it is known that no scientific investigation was had, and the returns, so far as the question of causes is concerned, are probably therefore based upon common report, or the mere opinions of engineers. (To be continued.)

SPECIFICATIONS OF ENGLISH PATENTS ENROLLED DURING THE WEEK ENDING 13TH OF SEPTEMBER, 1849.

None.