PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 637 



carbonic acid gas and uncombined nitrogen gas from the air are passed 

 from the generator to the piston, which is in the form of a hollow plunger, 

 so arranged that it is packed and fitted only at the top, where there is the 

 least heat. In this way, the common difficulty of lubricating a hot cylinder 

 and piston is obviated. The generator of heat is surrounded with fire-brick 

 or soap-stone, which prevents the iron from being burnt. The engine is 

 single-acting — that is, the power is applied to the piston moving in one 

 direction, during which movement the air to feed the fire is pumped in; the 

 momentum acquired at the same time by a balance or fly-wheel, is used to 

 carry the piston back to its original position. The diameter of the air- 

 pump in the engine at the Fair is twelve inches; that of its piston is six- 

 teen inches; the difference of the areas in the pump and piston, mutiplied 

 by the usual pressure, eight pounds per square inch, shows that this engine 

 exerts a two-horse power. It requires about ten pounds of coal per hour. 

 It occupies five square feet of room, and weighs 3,000 pounds. 



Mr. Bartlett thought this plan for using the products of combustion, one 

 justly deserving our careful consideration. 



The Chairman said an engine was invented by Blanchard which used 

 both steam and the products of combustion. A steamer was built on this 

 plan, and run for some time in New York harbor. A committee from this 

 Institute examined it, and reported a saving of fuel by the arrangement. 

 But when the steamer was put on a regular route, it was found she was 

 not always to be relied upon. The combustion in this plan was carried on 

 under pressure; the steam was used on one side of a piston and the gaseous 

 products of combustion on the other. There was danger in that arrange- 

 ment that the cylinder would be marred by the solid particles in the pro- 

 ducts, but in the plan before us this defect is remedied. Many persons 

 have been deceived by sanguine statements regarding air or caloric engines. 

 It is not claimed for this plan, as has been for nearly all others of this class, 

 that it is a great saver of fuel. In fact, it takes a little more than the best 

 eteam engines; but it is safe, convenient, and will not burn out so rapidly 

 as those having the iron cylinders in direct contact with the fire. 



Dumping "Wagon. 



Mr. Davis exhibited a model of a new dumping wagon, which could also 

 be used for the ordinary work of a farm. It is a Vermont invention. The 

 wagon is divided into several compartments, and the load in each is bal- 

 anced so as to be readily discharged. 



Mr. A. L. Fleury addressed the Association on the separation of gold from 

 quartz and other ores. 



After alluding to the ordinary process of extracting gold by means of 

 mercury, which forms an amalgam easily separated by heat, the speaker 

 said the general opinion has been that as gold is nineteen times heavier 

 than water, all the particles would sink in this liquid. Prof Faraday has 

 shown that when chloride of gold in solution was placed in a bottle, and 

 gradually small portions of phosphorus were added, the gold, instead of 

 sinking to the bottom, remained suspended in the liquid, giving to it a fine 

 red color. Does this curious fact — explaining to us the deplorable loss of 

 at least fifty per cent of gold in the ordinary washing process — not iudi- 



