PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 441 



previous to the coal era, but we have no evidence of the existence of man 

 before that period. 



The SuPER-HEATiNG OP Steam. 



Dr. Warren Rowell. — A few days ago, I made an examination of the 

 engines of the new steamship Scotia, and their method of super-heating. 

 There are seven flues in the boiler, two feet in diameter and fourteen feet 

 long, through which the heat passes. These flues also act as super-heaters. 

 The pressure of steam is about twenty-five pounds, which is super-heated 

 an additional sixty degrees. The scale which forms on the tubes in the 

 boiler is picked off every trip. The engines are side-levers. The economy 

 which is claimed for the super-heater is about seven per cent. I have been 

 informed that a super-heater has been attached to one of the government 

 vessels running from Washington to Fortress Monroe, and that the steam 

 was super-heated so much that the pressure was greater at the end than at 

 the commencement of the stroke. 



Mr. T. D. Stetson. — I presume that the conclusion is, that super-heating, 

 when carried to a certain extent, makes up for the loss of pressure at the 

 end of the stroke, and that beyond a certain point there is no economy. 



The Chairman. — Mr. Allaire, of this city, was the first to use the steam 

 drum. The question is, whether there is not enough super-heating obtained 

 from this iirrangement? 



Mr. J. K. Fisher. — By heating steam too mueh, as in some cases of super- 

 heating, the lubricating qualities of steam are lessened. I have heard rail- 

 road men say that when going down hill they shut off steam; and after a 

 time, they say, the engine begins to "howl," as they term it. The brass 

 rings used in the piston are what cut and make this noise. Much of this 

 cutting I attribute to the use of different metals; foi', with steam said to bo 

 nearly red hot, and cast iron rings used in the piston, the cylinder is not cut. 

 That is, cast iron upon cast iron, I am told on good authority, does not cut. 

 This subject is one that should be carefully experimented upon. 



Prof Vandcrweyde. — Two metals working together, if of the same 

 nature, will wear evener and work better than if two different ones are 

 used. A soft substance will cut a hard one, as is seen in boring through 

 glass with copper. The emery beds itself in the copper and acts like teeth 

 in a saw. In the same way, a stone is cut with an iron saw. I had occa- 

 sion lately to saw a piece of silex in which there was some copper; I found 

 no difficulty in cutting the silex, but, on reaching the copper, the emery 

 left the iron saw and became imbedded in the copper and cut the saw. 



Dr. Warren Rowell. — I have been told that they sometimes find in loco- 

 motive cylinders, within the piston, fine balls of something that resembles 

 charcoal. This would appear to be derived from the carbonization of the 

 oil. At 310 degrees, vulcanized india-rubber is decomposed, and, in super- 

 heated steam, a much higher temperature is used. 



Prof Vandcrweyde. — The iron may have much to do with this carboni- 

 zation of the oil. Metals have an effect on the oil, and may decompose it, 

 I have no doubt that in locomotives, where they use a very high tempera- 

 ture, the oil being in close union with the metafs, chemical decomposition 

 takes place. The metal of the boiler will have an effect on the oil, the 



