=Boiler Experiments.=--The first boiler which I made was constructed something on the Herreshoff principle, but instead of having one simple pipe in one very long coil, I used a series of very small and light pipes, connected in such a manner that there was a rapid circulation through the whole--the tubes increasing in size and number as the steam was generated. I intended that there should be a pressure of about 100 lbs. more on the feed water end of the series than on the steam end, and I believed that this difference in pressure would be sufficient to ensure a direct and positive circulation through every tube in the series. This first boiler was exceedingly light, but the workmanship, as far as putting the tubes together was concerned, was very bad, and it was found impossible to so adjust the supply of water as to make dry steam without overheating and destroying the tubes. [Illustration: Fig. 90.--Steam boiler employed in my experiments. With this boiler, I had no trouble in producing all the steam that I could possibly use, and at any pressure up to 400 lbs. to the square inch.] [Illustration: Fig. 91.--The burner employed in my steam experiments. This produced a dense and uniform blue purple flame 20 inch deep.] Before making another boiler I obtained a quantity of copper tubes, about 8 feet long, 3/8 inch external diameter, and 1/50 of an inch thick. I subjected about 100 of these tubes to an internal pressure of 1 ton per square inch of cold kerosine oil, and as none of them leaked I did not test any more, but commenced my experiments by placing some of them in a white-hot petroleum fire. I found that I could evaporate as much as 26-1/2 lbs. of water per square foot of heating surface per hour, and that with a forced circulation, although the quantity of water passing was very small but positive, there was no danger of over-heating. I conducted many experiments with a pressure of over 400 lbs. per square inch, but none of the tubes failed. I then mounted a single tube in a white-hot furnace, also with a water circulation, and found that it only burst under steam at a pressure of 1,650 lbs. per square inch. A large boiler, having about 800 square feet of heating surface including the feed-water heater, was then constructed. It is shown in Fig. 90. This boiler is about 4-1/2 feet wide at the bottom, 8 feet long and 6 feet high. It weighs with the casing, the dome, the smoke stack and connections, a little less than 1,000 lbs. The water first passes through a system of small tubes--1/4 inch in diameter and 1/60 inch thick--which were placed at the top of the boiler and immediately over the larger tubes--not shown in the cut. This feed-water heater is found to be very effective. It utilises the heat of the products of combustion after they have passed through the boiler proper and greatly reduces their temperature, while the feed-water enters the boiler at a temperature of 250° F. A forced circulation is maintained