308 



OPTICAL PROJECTION 



internal bore J inch diameter for the hydrogen, surrounded 

 by oxygen. Hydrogen is made in a bottle with zinc scraps 

 and dilute hydrochloric acid, tke chloride of sodium, lithium, 

 or calcium being dissolved in the water to saturation; and 

 to assist the rush of gas and carry up more of the spray of 

 the liquid into the flame, either hydrogen or coal-gas is also 

 passed through the liquid by the ordinary wash -hot tie method. 

 When the oxygen is properly adjusted, the lines are pretty 

 bright. Bright lines may also be shown upon the continuous 

 spectrum, by melting the chlorides of the alkalies, upon the 

 surface of a hard lime cylinder, and using this in the ordinary 

 way. 



The brightest method of projecting the sodium line with 



PIG. 168. Combustion Lantern 



the oxy-hydrogen flame is that adopted by the late Mr. 

 Spottiswoode. A jet for burning the two gases is furnished 

 with a hollow chamber in the course of the hydrogen tube. 

 Into this chamber is introduced some metallic sodium, and 

 the chamber is heated in a Bunsen burner; the gas then 

 carries over with it a copious supply of sodium vapour, which 

 burns with intense brilliance at the orifice of the jet. 



The lines of some alkaline earths may also be excellently 

 shown by a simple apparatus devised by Prof. Weinhold, and 

 shown in figs. 168 and 169, fig. 168 being a plan one-third 

 the natural size, fig. 169 a perspective view on a smaller 

 scale. The body is a small cubical lantern, with a door at the 

 back fastened by the catch g, and with a nozzle on the front 



