MECHAXIQS AND USEFUL ARTS. 59 



before the Institution of Mechanical Engineers at Manchester, England. 

 'He constructed small vertical boilers of equal dimensions, and placed in the 

 centre of each a single tube, two inches in diameter, and of No. 14 wire 

 gage thickness. A gas flame was applied to each tube iron, brass, and 

 copper successively, during a certain period of time, which was equivalent 

 to the same quantity of fuel consumed in each case. The experiments were 

 first conducted during the day, then at night, at times when there was little 

 probability of a change of pressure in gas pipes. Eight of these were made 

 with the boilers, and the quantity of water evaporated was measured by the 

 number of inches it was lowered in a boiler by each experiment. The result 

 was in favor of the greater evaporating power of the brass over the iron 

 tubes, in the proportion of 125 to 100 ; that is, two pounds or two tons of 

 coal, or other fuel, will, with the use of brass tubes in a boiler, evaporate 

 twenty-five per cent, more Avater than iron tubes with the same quantity of 

 fuel, under precisely the same circumstances. In the same proportion that 

 brass surpassed iron in evaporative power, copper was found to surpass 

 brass. The evaporative powers, relatively, of the three metals in tubes for 

 steam boilers, he found were as follows: Iron, 100; brass, 125; copper, 156. 

 The experiments of Mr. Tosh were subjected to a searching criticism by 

 the engineers of the Institution, and strong doubts were expressed as to their 

 correctness. 



PROSSER'S SURFACE CONDENSER. 



The principle of this condenser is to use much less condensing water than 

 is usual, by raising its temperature to the boiling point, and to condense the 

 steam arising from this water to supply the loss of water in the boiler. The 

 apparatus is divided into three portions. The condenser proper consists of a 

 number of iron pipes, inside of which runs the escape steam, and outside 

 of which is the condensing water. The condenser for the steam arising from 

 the condensing water is built on the same plan. The heater through which 

 the condensed water is forced to pass on its way back to the boiler, and where 

 it is heated by the escape steam on its way to the condenser, is also of a sim- 

 ilar construction. There are merits in this condenser. It is so constructed 

 as to be lasting, and it leaves the boiler clean, even when the most dirty 

 water is used. 



ON A NEW SOUNDING APPARATUS. 



The following device, proposed by Lieut. E. B. Hunt, U. S. A., has for its 

 chief object to run sounding lines in harbors and water of moderate depth. 

 The principle is that of measuring barometrically the pressure due to the 

 depth, this pressure being transmitted to the barometric basin by a column 

 of atmospheric air. 



The method is as follows : Arrange a weighted india-rubber vessel for drag- 

 ging on the bottom; connect this with a boat or surveying vessel by an air- 

 tight tube of small bore; let this tube open into a cistern of mercury made 

 air-tight; from this cistern arrange a vertical glass column, open at the top, 

 in which the mercury can freely rise to any required height by the pressure 

 due to depth. 



The mode of use would be thus : " Throw the weighted air-vessel overboard 

 and let it sink to the bottom, it being connected with the vessel by the air- 



