proceedings of the polytechnic association. s45 

 Substitute for Lucifer Matches. 



M. Pcltzer proposes, as a substitute for compouuds containing- phos-- 

 phorus, a violet powder, made by mixing a solution of sulphate of copper 

 saturated with ammonia and an equal volume of the solution of sulphate 

 of copper saturated with liA'posulpliate of soda. Tiiis powder mixed with 

 the chlorate of potash will take iire by percussion or rubbing, 



Preservation of Chloroform. 



V 



M. Boeltger finds that fragments of caustic soda in a bottle containing" 

 chloroform will prevent its decomposition by exposure to sunlight. 



New European Uailway. 



Tiic railway connecting the capitals of France and Spain has just been 

 completed. The distance between Paris and Madrid is 840 miles; the time 

 of passage is 35 hours; the price in a first-class car 165 francs, or about $32, 



The Maximum Pressure on Car Wheels Changed by Direction, 



Mr. (r. l^artlett asked a question regarding the relative power of the 

 crank directly above and below the axle in the locomotive, which led to the 

 discussion of another interesting point b}- the Chairman, proving that the 

 driving wheels of a locomotive would have the greatest adhesion to the 

 rail, when under motion, if they were placed forward, so as to sustain the 

 entire weight of the front end of the locomotive. To further explain his 

 position, the Chairman drew a diagram on the blackboard, illustrating a 

 car-brake patented a fjw j'ears ago; there was an action about it mj'ste* 

 rious at first to the invcntcn', which he would explain. The brake con-* 

 sists of two similar cone-wliecls, which are pressed into the two wheels of 

 the truck on the same side. When pressed in far enough the friction will 

 make the cone-wheels revolve with the ti'uck wheels. These two cone-» 

 wheels if geared together, would run in opposite direction; but as they are 

 as far from each othfr as the two truck wheels, two intermediate wheels 

 were placed between, gearing into the main cone-wheels, so as to compel 

 them to move in opposite directions; thus arranged they are pressed 

 against the truck-wheels, and one -or the other wheel would be reversed 

 instantly. If unning in either direction the hind wheel would always reverse. 

 To t.-xplain this he drew a parallelogram— the line a b representing the 

 lower .side, and the line ah the upper. Let the line a b represent the rail 

 and the point of contact between the rail and the two wheels of the truck 

 by A and r respectively. Draw the diagonal lines Ab and sa; if ab repre- 

 sent the momentum of the truck going in either direction, and the perpen- 

 dicular line AU the weight sustained, the diagonal line represents the sum 

 of these two forces. When the truck moves in the direction a, the diagonal 

 A& represents the direction of the united forces; there is, therefore, a 



