PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 387 



inch apart, all arouiul, to which the pljites arc riveted. The object of tliis 

 arrangement is to allow the heat to pass inward more rapidly than it could 

 throug-h the ordinary thick cylinder. The cylinders used in the Metropolitan 

 mills are thus constructed. None of the steam which goes into the casing 

 is used in the cylinder. It passes into the jacket on the upper side and 

 drips out in the form of water through a small hole on the under side. 



The chairman remarked that the most effective way of using steam was 

 through Avide and straight channels leading from the boiler to the cylinder, 

 Narrow and tortuous channels have the eflect of throttling the steam. The 

 plan explained by Mr. Stetson is 0{)en to this objection. 



The Great Rodman Gun. 



Mr. Secretary Garvey read, from a New York paper, an account of the 

 first firing of this gun at Fort Ilamiltou on Wednesday. It was first 

 charged with 50 pounds of powder and a blank cartriTlge. At the second 

 and third discharges the gun was shotted. The amount of powder used 

 was 100 lbs., and the weight of the ball nearly eleven hundred. This trial 

 was satisfactory. Another is to take place in the course of a few 

 weeks. 



Mr. Stetson described the Rodman gun, and the peculiar mode of casting 

 it, and of cooling the casting from the inside by means of a water tube in 

 the core. The trial made, he did not regard as a test, for the amount of 

 powder used was comparatively small. In the ordinary service charge, the 

 weight of powder is one third of that of the shot. 



Mr. Garvey thought it might be readily demonstrated that the larger the 

 gun, the less would be the proportion of powder rf^quired. There have 

 been many erroneous statements made with regard to the long range of 

 guns. From calculations he had made he was convinced that to carry a 

 ball ten miles was an utter impossibility^ 



The Chairman then read the following notes of scientific progress: 



Electricity of Metals. 



M. Gaugain stated before the Paris Academy of Sciences that he had 

 experimented with metals to ascertain the order in wliich they are charged 

 by frictiou with positive or negative electricity, and by means of sulphur 

 with which nearly all the metals are negative, and gutta percha with 

 which they are positive, he has succeeded in forming the following list 

 where each metal is positive to those following it and negative to those 

 which precede. Those enclosed in brackets behave in nearly the same 

 manner. 



Aluminum. — [Zinc, Cadmium, Lead], [Iron, Tin], [Copper, Bismuth], [An- 

 timony, Silver], [Mercury, Gold, Palladium]. 



Analysis of the Human Breath. 



A new and extremely delicate instrument has been made, under the direc- 

 tion of Prof. Tyndal, by Mr. Barrett, an assistant teacher in the Royal 

 Institute, London, for determining the amount of carbonic acid gas exhaled 

 by the lungs under different conditions. The contents of a bag, filled with 

 human breath deprived of its moisture, enters an exhausted brass cylinder 



