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(10644) W. G. H. writes: In a work upon electricity supposed to be reliable I find What is termed the "electromotive series" given exactly in the order of the following elements, namely : Zinc, cadmium, tin, lead, iron, nickel, bismuth, antimony, copper, silver, gold, platinum, graphite. The book says that the element which is acted upon by the electrolyte is always positive to the other. A writer in the SCIENTIFIC AMERICAN SUPPLEMENT gives a different explanation, and a variation in the order of the series. In the issue of July 13, 1907, A. Lang in an article upon galvanizing says : "The reverse of the order in which I have previously placed the metals in relation to their conductivities, i. e., antimony, zinc, lead, tin, iron, and copper, indicates the positive direction in which the current will flow from metals having the higher to those having the lower potential." Mr. Lang bases the order of the series upon the conductivities of the metals. A. The table of contact difference of potential used in the article by A. Lang, to which you refer in your inquiry, is based upon Ayrton and Perry's experiments, and is essentially the same as is given in Everett's "Units and Physical Constants," and the Smithsonian Physical Tables. We do not know any better authority, and should accept it as correct. The disagreement of authorities cannot always be explained. T." 'ml j we may take a later authority in place of an earlier one. The difference between tin and lead is so little that one might easily be mistaken in assigning the places to these two. (10645) E. S. A. asks: What modern methods are used for ventilating motor and generator armatures of various types ? A. Modern electrical generators ant motors are designed so that the rise in temperature shall not exceed a certain amount. No special mechanical provision is required to ventilate or cool the armatures, although a large number of inventions for this purpose have been made. (10646) A. O. writes: A striking example of the effects of sound waves was noticed on September 15 at the morning session of the East Ohio Conference, held in the First Methodist Episcopal Church of Cleveland. During the singing of a hymn by the congregation, which numbered about twenty-five hundred, a large chandelier, weighing over a ton, was set in motion. It is hung by a chain about forty feet in length from the center of a large tower placed over the center of the church. No explanation can be given for the fact save that the walls of the tower so condensed and reflected the sound waves that they started the huge pendulum-like chandelier to swinging. A. Your observation is interesting. It is doubtless true that the chandelier was set swinging by the waves of sound. Church windows have many times been brcken by the same means. Some note occurs to which the chandelier chain can respond in sympathetic vibration. It must not be supposed that a force equal to a ton or more was exerted to swing the chandelier. A minute force applied many times, in time with the vibration period of the chandelier, set it to swinging. (10647) R. B. writes: Correction to reply in Notes and Queries column, No. 10618, September 28, 1907, "Oxalate of Lime Process for Concrete Tanks." The use of hot paraffin wax to impregnate the concrete tank for gasoline storage would be impracticable, owing to the fact that paraffin is exceedngly soluble in gasoline and would therefore be promptly dissolved out of the concrete walls, causing excessive seepage of gasoline through the walls into the ground. A far more perfect gasoline-tight tank could be made by brushing over the walls wth hydrochloric acid, sp. gr. 1.10, applying the acid freely, having it previously warmed to about 80 deg. C, allowing it to react on the calcium compounds in the concrete, and aftei- an tour or so, go over the surfaces again with a strong hot solution of ammonium oxalate, brushing it fi-eely and allowing it to r-eact on the calcium chloride produced by the hydrochloric acid. This process fills the pores of the concrete with the insoluble compound calcium oxalate, which is insoluble in water or gasoline and entirely stable and permanent. After applying the oxalate solution, allow the walls to dry and then re- move any soluble salts formed by the chemical reaction by washing down with water. The tank after drying again is ready for the reception of gasoline. The writer treated a tank in this manner for holding gasoline for laboratory purposes and finds it perfectly tight after a year's service. It is needless to say that the walls must be bone dry before applying the acid in order to get the best results.