What have you previously learned concerning the volumes of hydrogen and chlorine that unite? The hydrogen of the ammonia (NH,) united with the chlorine. What volume then of hydrogen was used? What became of the nitrogen originally with this hydrogen? What is the volumetric composition of ammonia? The actual volumes of chlorine and nitrogen can be determined by measuring the water the tube holds and the volume of the resulting liquid, and subtracting. However, if the tube has a uniform bore the comparison of the lengths of the columns is much simpler and more satisfactory. A SIMPLE RESONATOR. M. A. COBB, LANSING, MICH. A short time ago I noticed the similarity between a Helmholtz resonator and an incandescent light bulb. Acting upon this observation I broke the tip of a bulb and enlarged the opening by means of a file and punched in the cavity carrying the wires. Holding the small orifice to the ear and the other towards the source of sound as the key board of a piano the air resounds-that is, the sound is louder when its natural period of vibration is struck. "Phonograph tubes may be used to transmit sound to the ear. you. The bulb is similar to a Helmholtz resonator and its action is familiar to The ordinary size, 16 c p bulb, with a small opening, responds to about 256 vibrations. As the bulb becomes larger the pitch lowers and vice versa. Here is a 294 c c bulb, the note is c; a 167 c c, the note is e. As the area of the orifice becomes larger the note is higher; the note of a bulb can be changed by enlarging the orifice. There appears to be no simple relation between volume or area to the pitch. Londhauss gives the formulæ for circular and flask with a neck as: I found the constant to be much lower, but with the means at my command could not get check or reliable results. The bulbs can be used for resonators for analysis of sound and deter mining the characteristics of quality. For instance, I found a bulb to resound strong for middle "c," weak for c, and faint for g, proving that the latter strings of the piano were vibrating in two or three parts respectively. Interference of waves at the edges of a tuning fork can be clearly demonstrated by holding the bulb in various positions and using the phonograph tubes. I have fair results in determining the vibration rate of a note by means of the siren, noting when the siren and a resonator were in unison. The resonators show clearly that confined air has a vibration rate of its own and vibrate freely when the vibrating body is of the same rate. A CONTACT KEY FOR A SLIDE WIRE BRIDGE. H. L. CURTIS, MICHIGAN AGRICULTURAL COLLEGE. In designing a contact key for a slide wire bridge the following things need to be considered. It should be possible to operate the key easily. The electrical contact within the key should be good. Either the zero point or the point of contact should be adjustable, so that the two may be brought into coincidence, yet when once adjusted there should be no danger of either of them changing. It should not be possible to apply undue pressure on the point of contact. A key which answers all of these requirements except the last, is described in Price's "Measurement of Electrical Resistance." The key about to be described is very similar to this, but has an added feature to overcome this defect. The key is illustrated in the drawing. It slides on a meter stick which is raised a short distance from the base of the bridge. A piece of insulating material (wood fiber is cheap and satisfactory), prevents the wire from touching the metal above. Also because of the wire sliding in grooves, it will always be underneath the platinum point, so that contact is certain when the key is pressed. の Ө Fastened to the frame is a tapping key. Underneath the vulcanite top of this is a stop, which strikes the meter stick when the key is pressed. To this is soldered a thin piece of spring brass, which carries the platinum contact. The contact point may be made to coincide with the pointer by moving the tapping key in slots (not shown in the drawing) where this is fastened to the frame. This key has been used for two terms, and has given very satisfactory results. A SIMPLE STEP-UP AND STEP-DOWN APPARATUS. DE FORREST ROSS, YPSILANTI. The above heading, though not a misnomer, covers only a part of the possibilities of this simple and inexpensive apparatus. As many of the high schools are now equipped with the alternating current for lighting purposes, it occurred to me that this current might be used for demonstration work in the physical laboratory. The electro magnet before you is the outgrowth of that idea, suggested by some experiments of Professor Carhart at one of our physical conferences. First, then, is to make the magnet, as, so far, I have been unable to find anything in the market that will answer the purpose. Procure of your R B hardware dealer twenty to twenty-five pounds of No. 16 annealed iron wire, and cut it into pieces about fifteen inches long. Bind these in a compact bundle with electric wire tape, and make the top level by driving the wires down with a hammer. This will constitute the core of the magnet. Fasten the core to the base in an unright position by cutting a hole in a board just large enough to admit the end of the core. Bend enough of the wires over around the outer edge to hold the core firmly in position and fasten them to the under side of the board with staples. Then by driving wedges between the wires, the core can be made to stand rigidly in its place. Nail another board on the under side to cover up the uneven ends of the core and it is ready for winding. Begin at the bottom and wind in smooth, close coils four layers of No. 12, double covered copper wire, to within one inch of the top and fasten the ends to binding posts in base. The whole coil should now be covered with electric tape. Several coils of well insulated copper wire should be made, varying in size of wire, diameter of coils, and number of turns in each. These should be fastened with tape for convenience in handling, leaving the ends long enough for connections. With a coil of fifty or sixty turns of No. 12 copper wire wound so as to fit rather loosely the primary coil, the terminals connected by a No. 16 copper wire, and the coil lowered to the centre of the magnet, an induced current will be produced strong enough to quickly fuse the wire and cause the copper to boil like water. Iron wire between the terminals will burn with brilliant scintillations. The operation, however, can hold the naked terminals in his hand without feeling the slightest effects of the current. This illustrates in a forcible way a step-down device. If a coil of five hundred or six hundred turns of No. 20 wire be used, the potential becomes so high that it will make an electric lamp glow intensely, and by attaching handles to the terminals and slowly lowering the coil from some distance above the magnet, a range of physiological effects will be experienced, varying from an almost imperceptible pulsation to that of sufficient strength to satisfy the most ardent. These are only suggestions of things one can work out, once started along this interesting line. You will also be surprised to see the interest your students will take and how much they will get from this, to them, most difficult part of electricity. CONSERVATION OF ENERGY WITHIN THE HUMAN BODY. ARTHUR W. SMITH, PH.D., UNIVERSITY OF MICHIGAN. The nutrition of the human body is a subject of great importance to every one of us. Whether we realize it or not, it is presented to us three times a day, and more or less wisely we attempt to reach a satisfactory solution of the problem. The question has also been attacked from the scientific standpoint by a number of investigators, and in the brief time at my disposal I want to give you the results of some experiments along this line. In so far as the material phenomena are concerned, life consists of transformations of matter and energy. It is commonly assumed that these transformations follow the laws of the conservation of matter and the conservation of energy, although the experimental proof that they do has been lacking. In order to show that the law of the conservation of energy holds true in the body one must be able to measure the energy received |