The Art of projection and complete magic lantern ... - Yesterday Image

i6iTrough, which consists of two glass plates with a layer of Indiarubberof half-an-inah in thickness, cut U shape, and laid betweenthe glasses, which are held firmly against the rubber by a screw-clampingarrangement in three different positions of the trough. The mountingand dismantling for cleaning are most complete and simple. Whenfitting up the trough, the sides of the rubber pressing against theglass should be smeared with glycerine ; so as to make a perfect connection,the screws should be fastened equally moderately tight ; whennot in use these screws should be loosened, allowing the glass plates toexpand or contract according to the temperature, otherwise they areliable to fracture.To each side of the trough is attached a metal rod provided withpliers and connections for a bicromate battery of two or more cells.The trough is placed on the table in front of the condenser, and theconnections made with the communicator which allows the current to bereversed or broken, this being in connection with a " Grove's " batteryor pile of 3 or 4 volts.The experiments which can be made with the aid of this instrumentare so numerous, that it is impossible to enumerate them all, but wegive a few of each group that are very simple.ELECTROLYSIS.Faraday has given the name of " ekctrolysation " to the decompositionof a substance which is composed in its element, by the passage of anelectric current, this phenomena can be easily demonstrated with thelaboratorial trough.Decomposition of Water. We know that water is the result ofthe combination of two parts of hydrogen and one of oxygen. Todemonstrate this, fill the trough with water which has been made slightlysour with sulphuric acid (to increase its conducting properties), attachtwo perfectly straight threads of platinum to the two pliers :after havingplaced the first perfectly upright in the water, place the second wireupright in the same manner, upon passing the current through, a numberof fine globules issue from one side (oxygen), and from the other theevolution is much more rapid and the bubbles much larger (hydrogen.)This is a very old experiment and dates from the beginning of thiscentury, being discovered by Carlisle and Nicholson.Collection of Hydrogen by Palladium. In the case will befound a strip of white metal which terminates in a spiral form, and is