The spring when in use was always exposed to steam of atmospheric pressure. At this temperature of 212° we found by careful experiment that all the springs were weakened equally, namely, one pound in forty pounds. So the springs were made to show, when cold, 39 pounds instead of 40 pounds, and in this ratio for all strengths.
This system of manufacture and testing was examined in operation by every engineer who ordered an indicator, the shop on St. Martin’s Lane being very convenient. They generally required that the indicator should be tested by the mercurial column. The Elliotts, being large makers of barometers, had plenty of pure mercury, so this requirement was readily complied with, and the springs were invariably found to be absolutely correct. We never used the mercurial column in manufacturing, but were glad to apply it for the satisfaction of customers.
I employed the following test for friction. The indicator when finished was set on a firm bracket in the shop. The spring was pressed down as far as it could be, and then allowed to return to its position of rest very slowly, the motion at the end becoming almost insensible. Then a fine line was drawn with a sharp-pointed brass wire on metallic paper placed on the drum. The spring was then pulled up as far as possible and allowed to return to its position of rest in the same careful manner. The point must then absolutely retrace this line. No indicator was allowed to go out without satisfying this test. The workmanship was so excellent that they always did so as a matter of course.
Mr. Henry R. Worthington once told me, long after, that on the test of an installation of his pump in Philadelphia, after he had indicated it at both steam and water ends, the examining board asked him to permit them to make a test with their own indicator, which they did the next day. They brought another indicator, of Elliott’s make like his own, but the number showed it to have been made some years later. “Would you believe it,” said he, “the diagrams were every one of them absolutely identical with my own!” I replied that the system of manufacture was such that this could not have been otherwise.
Plan of Spring-testing Instrument.
I wish to acknowledge my obligation to Elliott Brothers for their cordial co-operation, their excellent system of manufacture, and the intelligent skill of their workmen, by one of whom the swiveling connection of the levers with the piston-rod was devised.
The indicator was improved in other important respects, but I here confine myself to the above, which most directly affected its accuracy. This soon became established in the public confidence. During my stay in England, about five years longer, the sale of indicators averaged some three hundred a year, with but little variation. The Elliotts then told me that they considered the market to have been about supplied, and looked for a considerable falling off in the demand, and had already reduced their orders for material. Eight years after my return I ordered from them two indicators for use in indicating engines exhibited at our Centennial Exhibition at Philadelphia. The indicators had from the first been numbered in the order of their manufacture. These came numbered over 10,000.
The indicators were put on the market in the spring of 1863, and I sought opportunity to apply them on locomotives. In this I had the efficient co-operation of Zerah Colburn, then editor of The Engineer. The first application of them was on a locomotive of the London and Southwestern Railway, and our trips, two in number, were from London to Southampton and return. The revelations made by the indicator were far from agreeable to Mr. Beattie, the chief engineer of the line. Mr. Beattie had filled his boilers with tubes ⁷⁄₈ of an inch in diameter. The diagrams showed the pressure of blast necessary to draw the gases through these tubes to average about ten pounds above the atmosphere, the reduction of the nozzles producing this amount of back pressure throughout the stroke. Another revelation was equally disagreeable. The steam showed very wet. We learned that Mr. Beattie surrounded his cylinders with a jacket. This was a large corrugated casting in which the cylinder was inserted as a liner. To keep the cylinder hot the exhaust was passed through this jacket. Mr. Colburn made both of these features the subjects of editorials in The Engineer, written in his usual trenchant style. The last one was entitled “Mr. Beattie’s Refrigerators,” and produced a decided sensation.
Our next trips were made on the Great Eastern Road, one from London to Norwich and one from London to Great Yarmouth. On these trips we were accompanied by Mr. W. H. Maw, then head draftsman of the Great Eastern Locomotive Drawing Office, under Mr. Sinclair, the chief engineer, and by Mr. Pendred. These gentlemen were afterwards, respectively, the editors of Engineering and The Engineer.