^04 TRANSACTIONS OP THE AMEBICAN INSTITUTE. 



arrang-ement is the ability to maintain a vacuum more or less perfect, but, 

 nevertheless, equal both wiM^in and without the tubes, and thus relieving 

 the surface condenser from atmospheric pressure. The danger of fracture 

 caused by this pressure, as well as the impairing of the vacuum by small 

 leaks, are thus obviated, while, as it is only required to secure the tubes 

 against movement at one of their ends, the other ends may be left free to 

 move, and hence the disruption attending the expansions and contractions 

 cannot occur. These constitute the principal peculiarities of the Pirson 

 surface condenser, which the speaker proceeded to explain in detail by the 

 aid of a model, after which instances were given where resort to this 

 method, after other experiments had been tried, was successful. Over 

 8100,000 had been expended on the ocean steamer Adriatic, when the own- 

 ers were obliged to avail themselves of this plan. That their decision was 

 wise will be admitted upon examining the condensing apparatus of that 

 vessel. It contained over 5,000 tubes of copper, each 12 feet long and five- 

 eighths of an inch in diameter. The total length of tube being 60,000 feet, 

 or a little over 10 miles. This arrangement involved 10,000 joints, which 

 must be kept tight, and as the metal of the tubes must necessarily be thin 

 in order to transmit the heat from the steam within them to the cooling 

 medium without, if any one of them or of the joints failed, the vacuum 

 would be impaired. Therefore any plan which could secure to the engine 

 the usual vacuum, in spite of leakages, would be a valuable desideratum. 



In answer to a query whether a steamer could be run to Hong Kong 

 with the same fresh water, Mr. M. said: Theoretically the answer would be 

 in the affirmative, but practically this could not be done, on account of leak- 

 ages in the boiler, by which the fresh water would be wasted. As there 

 are usually several boilers in each steamer, it is a good plan to use, in one 

 of these boilers, salt water only, which would make up for the loss by leak- 

 age. In reply to an inquiry I'egarding the highest approximation to a 

 vacuum made with the surface condenser, Mr. M. remarked that 27 or 28 

 inches by the mercurial gauge could be produced; this, however, is at the 

 expense of temperature in the feed water, and as it is essential to carry the 

 feed water into the boiler as warm as possible, there would be, in reality, 

 no saving of fuel in approaching any nearer a perfect vacuum than as has 

 been stated. In the Cunard line of steamers the vacuum is carried at 24 

 inches, because of the increased quantity of injection water required, and 

 the consequent labor of the air pump. 



In order to guard against galvanic action it was fgund better to use pure 

 Spanish copper. It was preferable for this particular use to that from 

 Lake Superior, which contains an appreciable quantity of iron. It should 

 be observed that galvanic action also occurs on steamers which do not use 

 surface condensers. 



In concluding, Mr. Maynard alluded to another device for saving the 

 fresh water resulting from steam, the patent for which expired in 1860. It 

 consisted in the use of a fixed quantity of fresh water, to be used in the 

 ordinary jet for condensing the steam. Instead of throwing away this 

 water, it was cooled so as to be used again in the jet, by passing it through 

 a series of pipes, the exteriors of which were surrounded by cold salt water, 

 constantly forced in and discharged by means of a pump. In this case 



