assembling commutator segments or the working loose of some of the nuts or screws which are used to hold the parts in proper form will bring about a flat segment. A commutator may run eccentric because the armature shaft becomes loosened from the commutator shell in

some way. On account of the high rotative speed and the brush pressure the commutator would tend to wobble. The whole armature might chatter as a result of the irregular brush contact. If the mica insulation between adjacent commutator bars is harder than the metal, the copper will wear down a little faster and as a result, the brushes will be caused to vibrate and lose contact.

When a commutator is in good condition, its surface will have a deep bronze polish seeming as though glazed. It may have such a polished appearance and yet one or two bars may show that something is wrong. If we touch the commutator with the finger-nail lightly held against it when running, it will be possible to detect any roughness or irregularity in the surface. Similarly in the case of an eccentric commutator, if it be turned over slowly, the brushes can be seen to move up and down, whereas the usual rotative speed will cause the brushes to chatter. Eccentric running or high and low bars may even be so pronounced as to enable one to see through between the brushes and commutator. In examining railway motor and generator commutators, care must be exercised in handling when the line voltage is on the machine. In such equipment one side of the circuit is always grounded and it is a good precaution to see that one's self is effectively insulated from the ground.

In general, when sparking is due to any of the causes just mentioned, there is no effective remedy other than a removal of the armature from the motor and giving it proper attention in a lathe. Large generator or rotary converter armatures do not lend themselves to such methods. For machines of this class, a slide rest or bracket arrangement is available for fastening to the outboard bearing. The commutator turning tool is placed on this

slide and the commutator revolved at the proper speed either by turning over the engine or by other power conveniently applied. Only very fine cuts should be made and great care exercised in the performance of the work. A finish is made at higher speed with carborundum or sandpaper and a dead smooth file. There are also grinding tools on the market which are used for a similar purpose to that of the usual lathe tool. These are built up for use on a lathe or for attachment to a generator bearing.

If the proper care is exercised when a commutator is first put in service, it will not be difficult to get its color and polish. The first consideration is perfect contact between the brushes so that they bear uniformly, then keep the commutator clean and use just enough vaseline or lubricating compound to keep it running smoothly and quietly.

Boilers.

J. W. READING.

(Continued from February JOURNAL.) James Watt, by his genius and perseverance, exercised more influence over the development of steam power than perhaps any other individual. Newcomen had taken steps in the right direction when he built his atmospheric engines, and the progress that he made was greater than is usually imagined; yet his engine, as he left it, was clumsy and far from being economical.

James Watt started where Newcomen quit, carried the development much further, and when he left the steam engine it was a far more reliable machine than it was when he started to improve it; he made it capable of being used as a motive power for all the requirements of the times.

Watt's first attention to the steam engine came about by a very happy circumstance. He had returned to Greenock, after having worked some time in London, and was appointed mathematical instrument maker to the University of Glasgow. He was allowed to open a shop within the precincts of the university, for

the reason that trade jealousy prevented him becoming a regular instrument maker in the city. A model of Newcomen's engine, belonging to the university, having failed to act promptly, it was given to Watt for repairs. At a meeting held in the university later, June 10, 1766, a sum of £5 11s. was granted Watt for making alterations as well as repairs to the model. The choice of James Watt for this work was an exceedingly fortunate one and just the very thing to develop his fertile brain.

James Watt took out his first patent on the steam engine January 5, 1769. His new engine was entitled, "A new method of lessening the consumption of steam and fuel in fire engines." This patent included the use of a separate condenser and the expansive power of steam. From his having been the inventor of this use of steam pressure acting directly upon the piston, instead of only using the steam to produce a vacuum, it would naturally have been expected that he would have increased the working pressure of his boilers; but it seems Watt was prejudiced against high steam pressure. This prejudice was not shared in by Watt's partner, a man by the name of Matthew Boulton, who wrote him in July 1776 urging him to adopt higher pressures, saying, "As to boilers and steam pipes, let them be as strong as cannon; let it be applied in copper spheres within the water, and then four or five atmospheres will not compress such forms. The great boiler may be framed with scantlings of cast iron well screwed together with plates half inch thick, well fitted and screwed within; and then the greater the elastic force of steam the closer will they be pressed together, as the lid of a digester is."

The above description of Boulton is not very explicit, but he evidently saw the advantage of placing fire in copper fireboxes surrounded by water. Both Brindley and Smeaton had proposed methods of a similar nature.

While Watt was possessed of an amiable disposition, yet his dislike for high pressures led him to speak harshly of those

that advocated them. He was, apparently, so much occupied with his work upon the steam engine that he did not regard the more passive boiler with the respect and attention due it.

The well-known wagon boilers-a few that are still in existence-were introduced by Watt, or rather by his firm. He did not introduce the internal furnace flue, as all his early drawings of engines are shown with wagon boilers under-fired. Later, however, in one of his specifications, dated 1785, he shows a wagon boiler with an internal flue and an improved fireplace.

In a specification dated in 1782 Watt says, "I have not described the boilers that supply any, or all of these engines with steam, because I use such as are commonly applied to other steam engines."

The first steam engine made by the firm of Boulton and Watt seems to have been made in 1776 for the collieries of Bedworth. There is no record of the kind of a boiler used on this occasion. Dr. Robinson, a great friend of James Watt, says of the boiler, "This has received great improvements from his (J. Watt's) complete acquaintance with the procedure of nature in the production of steam. In some engines the fuel has been placed in the midst of the water, surrounded by an iron or copper vessel, while the exterior was made of wood which transmits and, therefore, wastes heat very slowly."

In Dr. Robinson's work there is a very interesting footnote by James Watt himself, which reads as follows: "The exterior part of large boilers was never executed in wood by me. This relates only to some of my models and one or two very small engines which I made of Newcomen's kind. They conveying the flame through flues in the inside of the water had been practiced by others before my time, and were common in Cornish engines. The inventor is unknown, but a person of the name of Swaine was a great propagator of the practice. However, I somewhat improved the forms and adjusted the proportions."

According to Trevithick, Charles Swaine worked as a rivet boy in making his

(Trevithick's) cylindrical wrought iron boilers.

James Watt, for some unknown reason, never was friendly with Trevithick and is said to have made remarks of a decidedly bitter nature against him, and may therefore have neglected to give the credit of the internal flue boiler to him. Smeaton's efforts as far back as 1758, also Brindley's about the same time-and while they were crude affairs-were undoubtedly the first steam engine boilers made with internal fireboxes.

There is some dispute as to who was the originator of the cylindrical boiler with internal flue, now universally known as the Cornish boiler. The honor, however, by some is given to Oliver Evans, an American inventor, and by others to Richard Trevithick, Sr. Trevithick's first cylindrical boilers were made so early that Swaine as a rivet boy could hardly have been old enough to have an insight into boiler construction and design at the time mentioned by Watt.

Murdoch, the right-hand man of Messrs. Boulton and Watt, made a model of a steam carriage in 1784, with a small copper boiler, the source of heat being a spirit lamp; the flames passed through a chamber in the boiler and out at one side of the top through a small chimney. The original is preserved in the art gallery at Birmingham, and is an interesting relic of one of the first carriages propelled by steam. The cylinder is partly within the boiler, which was the common practice in the manufacture of the early Trevithick engines.

As early as 1782 a steamboat was constructed by Marquis de Jouffroy, of Lyons, France. This boat, it has been said, ran for 15 months on the River Saone. It had a horizontal single cylinder engine, the cylinder being placed partly within the boiler for warmth, an idea that was subsequently followed out by Trevithick. A sketch of this boiler is exhibited at the South Kensington Museum, but no description is given.

Oliver Evans, an American millwright and engineer, sometime about the first of the eighteenth century, made a light

pressure engine. The boiler was cylindrical with a flue. In fact, it was built upon the same principle as the Cornish boiler heretofore mentioned. This boiler, however, was bricked up, the fire was placed underneath, the products of combustion passed along underneath the boiler and returned to the stack through the single flue. A diagram of this boiler is given in "Evans' Own Book." It is thought that the title of Evans' book was suggested for the reason that he did not think the world paid sufficient attention to his work as an engineer. In Article V of his work he describes boilers for high pressures, up to 120 pounds per square inch. They were plain cylindrical under-fired boilers about three feet in diameter and from 20 to 30 feet long, and were recommended for use where fuel was cheap. For great economy in fuel he recommended a double cylinder boiler -two cylinders-one inside the other, the inside boiler being placed a little below the center of the outside one, which was calculated to give room for steam on the upper side above the surface of the water. The water covered the inside boiler, inside of which fire was created. The barrel of these boilers was made of the best rolled iron. In Evans' description he says: "The ends may be made of soft cast iron, provided the fire be kept from them."

R. H. Thurston in his work gives a description of a boiler made by Evans which had a cylindrical shell and flue, as in the Cornish boilers, but under-fired, the flames first passing under the shell, then back through the tube to the stack. Thurston further remarks that this form of boiler was in use by both Evans and British engineers about 1800. If the date is correct, Evans must have been using cylindrical boilers at the same time or a little before Trevithick.

Luke Hebert, writing in 1835, says: "Next to the wagon shaped boilers of James Watt, those of cylindrical form have been most used, especially for highpressure engines. They are usually known in this country as Trevithick boilers, from the supposition that Trevi

thick invented them. We, however, observe that Mr. O. Evans described them as being used by him for his high-pressure engines prior to Trevithick's patent, and as Evans does not claim them we may suppose that they were in use before his time."

In the year 1786 a man by the name of Fitch tried to solve the problem of propelling boats by steam. He appears to have built a steamboat, but unfortunately, the only thing known about the boiler is the fact that it was not strong enough to do its work. In this same year William Symington submitted a working model of a steam carriage to the inspection of a body of scientific men in Edinburgh. No description of this boiler can be found.

In October, 1788, Symington fitted a boiler and engine to a pleasure boat which seems to have been fairly successful. Mr. Scott Russell says of the boiler in this boat: "It was compact and contained the fire wholly within it." Here again knowledge is lacking of particulars. It may have been a flue boiler of the kind afterwards used in marine work. In one description of this boat the chimney was said to have been built of brick.

In 1803 Symington was employed by Lord Dundas to fit up a boat with a steam engine. This, the first practical steamboat, was named the "Charlotte Dundas."

From figures given of this boat the boiler may have been of wagon shape or possibly cylindrical, and the stack appears to have been at the same end as the fire door. An engraving of this boat was made but no detail of the boiler is shown. The engine is described as being doubleacting, the earlier ones of Symington being single-acting atmospheric engines. Fincham, in his "History of Naval Architecture," gives a good description of the boat, but not of the machinery.

If

the engine was of the double-acting type, it would imply the use of a higher pressure of steam than was required for the atmospheric engine, and it would be of decided interest if a description of the boiler could be found. The "Charlotte Dundas" was laid up in a creek near

Bainsford Bridge, and exposed to public view as a wreck for many years. She was abandoned on account of injury to the canal banks from the wash caused by her paddle wheels.

It is recorded that Nathan Read, of Salem, Mass., took out a patent for a tubular boiler in 1791. The boiler was vertical in design, and of a construction which appears more recent than implied by the date. Tubular boilers are reckoned to belong to a much later date than 1791, yet a few isolated designs may be found recorded in various books and papers, this boiler of Read's being one of them. Read's boiler was intended for use with fire engines.

Count Rumford, under whose direction the boilers for heating the lecture room at the Royal Institution were made, adopted another method, that of dividing the water up in a number of small cylinders, around which the flames circulated. This boiler was designed in 1796 and is of special interest as a link in the chain of development of the modern water tube and sectional boilers. Although this boiler was used only to supply steam to heat the building, yet it is worthy of note as being the first of its kind recorded.

Probably no man contributed more to the use of high pressure and the development of the steam boiler than Richard Trevithick, Jr. He was a man of large inventive genius, but of somewhat erratic habits, and was never given the credit due him. His son, Francis Trevithick, collected a large amount of information and published an interesting story of the life of his father. Richard Trevithick, Jr., seems to have inherited the genius of his father, Richard Trevithick, Sr., who about the year 1775 made history in boiler development.

Richard Trevithick, Jr., made a number of improvements in designs for high pressure boilers, and on Christmas eve, 1801, tried a road locomotive at Camborn. Little is known of this engine except that it actually ran upon the wagon road and was the first locomotive that took a load of passengers-some seven or eight-men, who were with difficulty persuaded to ride

upon it. Eventually, it seems to have met the fate accorded to many more steam road carriages of later and better design. A figure is given of this steam carriage in the life of Trevithick, and the boilers appear to have been of cast iron with a return flue. A model of this engine can be seen in the South Kensington Museum.

In the history of the life of Richard Trevithick, Jr., he is credited with the building of a number of various designs of cast iron boilers, one of which is described as being four feet in diameter and one and one-half inches thick, and capable of withstanding a pressure as high as 145 pounds to the square inch. He was certainly a bold or reckless man, or probably a combination of both, which has often been found in great inventors and pioneers into new fields of research. Among his many inventions he seems to have devised the fusible plug and the lockup safety valve.

About the time Trevithick, Jr., in England and Oliver Evans in America were struggling with boilers for high pressure, we come across isolated cases of the use of wooden boilers of very low pressure, as mentioned in the February JOURNAL. A cut of these wooden boilers shows a horizontal section just above the fire grate, also longitudinal and cross sections. There was a flat combustion chamber at the back of the firebox, the top and bottom of which were stayed by short tubular castings forming water tubes, and from the back end of which an oval uptake smoke flue was carried by a bend and a return bend forward and back below the water line. The gauge was three feet by five feet, giving a surface of 15 square feet. The total heating surface was given as nearly 300 square feet. The construction of these boilers was highly ingenious, but with such material as wood could not have been very durable. Yet some of them seem-as in the case of the Philadelphia boiler-to have lasted for years. In the history of these wooden boilers the kind of wood used was not named.

In 1803 Trevithick had a locomotive running upon the railroad at Merthyr

Tydfil in South Wales. A drawing, taken from a model, shows the boiler to have been six feet long and four feet three inches in diameter, with return flue. There is some dispute as to the material used in this boiler, some claiming that it was of wrought, others that it was built of cast iron. However, the facts are that the shell was of cast iron and the return flue of wrought iron.

Another of Trevithick's locomotives, made for use in the north at Newcastleon-Tyne, about the history of which there is considerable obscurity, had apparently a wrought iron boiler with a return flue.

Two extremely valuable and interesting relics of old boiler work are preserved in the South Kensington Museum, both of Trevithick's make. One of these has a cylindrical cast iron shell, with wrought iron return flue. The other has a shell of cylindrical form, with a pocket for the engine cylinder at the back end, and is of one-inch thickness of metal. The front plate is of wrought iron in two pieces, riveted together and bolted on the flange of the shell. The bolt holes in the front plate are remarkable large and of square shape. The return flue was made of several small plates, and was riveted to the shell by means of angle irons and rings attached to the front plate. The construction of this return flue, which was made of five-sixteenths, of an inch plates, must have been a matter of great difficulty with the appliances then in use. It might be mentioned that the shell of this last described boiler was of wrought iron.

The relics of old boilers which have been handed down are so few that these two of Trevithick's make are of especial value for giving us an insight into the workmanship and methods of the early boilermakers.

In 1808 Mr. James Linaker, master millwright at the Portsmouth dockyard, made some experiments on propelling vessels by machinery. He proposed pumping water in at the head and discharging it at the stern. He had an engine and boiler made for his boat, but the results of his experiments are not recorded.